Immunology Flashcards
Which autoimmune conditions are palliated by pregnancy, which are exacerbated by pregnancy, and which have postpartum exacerbations?
RA and Graves disease seem to be palliated by pregnancy. SLE is exacerbated by pregnancy. Graves disease and myasthenia gravis are notorious for postpartum exacerbations.
Pregnancy increases the likelihood of SLE flares. The risk is highest in early pregnancy and during puerperium, with relative quiescence in the latter half of pregnancy. A lupus flare may be difficult to distinguish from pregnancy-induced HTN, as the features of HTN, edema, and proteinuria are shared. What lab value can help with this distinction?
Complement levels are low in SLE flare and normal in PIH.
Mortality is increased in pregnancy women with SLE, with most deaths occuring as a result of ___.
Mortality is increased in pregnancy women with SLE, with most deaths occuring as a result of pulmonary hemorrhage due to lupus pneumonitis and other complications (transverse myelitis, stroke, corticosteroid complications).
In addition to an increased incidence of IUGR and preterm labor, neonates born to mothers with SLE have a risk of congenital heart block. Why?
Antibodies to SS-A and SS-B (Ro and La) are thought to mediate this complication.
What laboratory investigations are often undertaken following two or more spontaneous abortions?
Parental karyotyping (karyotyping of an abortus is often indicated as well). Endometrial bxs may be obtained to exclude luteal phase defect (endometrial histology that is 2 or more days discrepant with dates). Endometrial culture may be obtained to exclude subclinical infection with U. urealyticum or C. trachomatis. Thyroid function tests. Tests for lupus anticoagulants.
CD5 is expressed by normal and neoplastic T cells (not expressed by very immature T cells) and a small, normally inconspicuous, B cells subset. In what non-malignant situation can patients have circulating CD19+/CD20+/CD5+ B cells?
Occasionally, patients have increased polyclonal benign circulating CD19+/CD20+/CD5+ B cells, particularly in rheumatoid arthritis.
What is the most frequent autoimmune disorder associated with ovarian teratomas?
Autoimmune encephalitis due to antibodies against the N-methyl-D-aspartate receptor (anti-NMDAR), a condition that frequently involves temporal lobes and hippocampus.
Its recognition is important, as removal of the ovarian tumor and early immunosuppressive therapy will often improve the outcome, with full recovery or only a residual mild neurologic deficit.
Goodpasture disease refers to the triad of ___, ___, and ___.
Goodpasture disease refers to the triad of pulmonary (alveolar) hemorrhage, glomerulonephritis of any severity, and serum anti-GBM production. The treatment of choice is plasmapheresis.
Goodpasture disease refers to the triad of pulmonary (alveolar) hemorrhage, glomerulonephritis of any severity, and serum anti-GBM production. What are these circulating antibodies directed against?
The NC1 domain of collagen IV in glomerular and alveolar basement membranes.
What 3 major categories of small vessel vasculitis can cause the pulmonary-renal syndrome?
Anti-GBM disease, ANCA disease, and immune complex-mediated diseases (such as SLE).
What is pulmonary-renal syndrome? What are causes of it?
The combination of acute glomerulonephritis and pulmonary hemorrhage. Causes: ANCA-positive vasculitis (granulomatosis with polyangiitis/Wegener’s, microscopic polyangiitis). Anti-GBM disease (Goodpasture’s). Pulmonary hemorrhage is a rare finding in lupus, HSP (IgAV), and infective endocarditis. Acute glomerulonephritis complicated by pulmonary edema due to fluid overload, as can occur in poststreptococcal glomerulonephritis.
What are 3 disorders in which linear IgG staining may be seen in glomeruli?
Diabetic glomerulosclerosis, fibrillary glomerulopathy, anti-GBM disease.
To what are c-ANCA and p-ANCA antibodies directed against?
c-ANCA: proteinase 3. p-ANCA: myeloperoxidase.
The Chapel Hill consensus conference recommendation on the nomenclature of systemic vasculitides is based primarily based on what?
It is based on the caliber of the most inflamed/affected vessels (the system does additionally incorporate IF findings and selected clinical/lab parameters). Small vessel vasculitis refers to changes found in distal vascular branches including arterioles, capillaries and venules. Medium vessel vasculitis is found in the main muscular arterial segments with multiple medial smooth muscle layers. Large vessel vasculitis is seen in the aorta and its largest branches.
What is the most common form of vasculitis in patients older than 50?
Giant cell arteritis (formerly termed temporal arteritis).
Giant cell arteritis (formerly termed temporal arteritis) is a granulomatous form of ANCA-negative large vessel vasculitis. What vessels does it tend to affect?
The aorta and its major branches, especially the extracranial arteries.
Giant cell arteritis (formerly termed temporal arteritis) tends to affect the aorta and its major branches, especially the extracranial arteries. Histologic appearance?
The inflammatory process, composed of mononuclear cells with a predominance of macrophages and lymphocytes, originates in the media and extends into the intima and adventitia. Multinucleated giant cells, of either the Langerhans or foreign body type, are found in about half of cases, often adjacent to the fragmented internal elastic lamina. Fibrinoid vascular wall necrosis is an infrequent observation and, when present, it patchy in distribution. GCA involves arteries in a segmental fashion, so a minimum of a 3 cm long segment should be obtained for an adequate histologic examination.
Giant cell arteritis is an ANCA-negative large vessel vasculitis. Is extensive fibrinoid necrosis consistent with giant cell arteritis?
No. In GCA, fibrinoid vascular wall necrosis is an infrequent observation and, when present, is patchy in distribution. The presence of extensive fibrinoid necrosis should raise the possibility of another type of systemic ANCA-negative vasculitis found in medium-sized vessels, such as polyarteritis nodosa.
When are antiphospholipid syndromes classified as primary, and when are they classified as secondary?
APS are classified as primary if they present with only a hypercoagulable state, and are classified as secondary if they are accompanied by other autoimmune disorders, such as SLE or other connective tissue diseases.
In antiphospholipid antibody syndrome, venous thrombosis is typically seen in deep leg veins (__%), as well as renal, hepatic, and retinal veins. Arterial thrombosis is typically seen in cerebrovascular (__%), coronary (__%), as well as ocular, mesenteric, deep leg, and renal arteries.
In antiphospholipid antibody syndrome, venous thrombosis is typically seen in deep leg veins (55%), as well as renal, hepatic, and retinal veins. Arterial thrombosis is typically seen in cerebrovascular (50%), coronary (25%), as well as ocular, mesenteric, deep leg, and renal arteries.
What is “catastrophic antiphospholipid syndrome”?
In rare instances (less than 1% of cases), multiple organ sites are affected by thrombosis simultaneously with dramatic clinical consequences and a mortality rate of up to 50%.
Thrombotic microangiopathy -a descriptive term- characterizes stenosing and/or thrombotic changes in small vessels (capillaries, arterioles, pre-arterioles, and small arteries). Veins and larger arteries with multiple layers of medial smooth muscle cells are characteristically spared. What are histologic features of the acute phase of a TMA?
The acute phase of a TMA is characterized by various changes that can be seen individually or in combination: (1) endothelial cell swelling and “mucoid” intimal widening with severe narrowing of vascular lumens; (2) intraluminal fibrin thrombi and/or fragmented RBCs in the intima and media; (3) necrosis of individual endothelial or medial smooth muscle cells; (4) PAS-positive nodular proteinaceous deposits replacing single necrotic arteriolar smooth muscle cells. Note: fibrin thrombi may sometimes be detected but they are not essential for establishing the diagnosis of a TMA.
Why is the “thrombotic” in thrombotic microangiopathy sometimes a misnomer?
Fibrin thrombi may sometimes be detected but they are not essential for establishing the diagnosis of a TMA.
The thrombotic microangiopathies are microvascular occlusive disorders characterized by systemic or intrarenal aggregation of platelets, thrombocytopenia, and mechanical injury to erythrocytes. TTP and HUS are both TMAs; What distinguishes them?
TTP affects mainly adults, with systemic microvascular aggregation of platelets affecting primarily the brain. HUS affects mainly children, with platelet–fibrin thrombi occluding predominantly the renal circulation.
The initial common event in the pathogenesis of all forms of thrombotic microangiopathy is severe endothelial cell injury that is caused by a wide variety of different agents. How reliably can the pathologist identify the underlying causative agent or event?
The pathologist generally cannot reliably identify the underlying causative agent or event and can often render only a descriptive diagnosis of TMA. The clinical distinction is not always clear-cut either and they are often clinically referred to as TTP-HUS.
Infection with EBV induces production of antibodies including IgG and IgM anti-viral capsid Ag (anti-VCA), anti-i, RF, ANA, and the Paul-Bunnell heterophile antibody. How sensitive and specific are heterophile Ab for EBV infection?
The heterophile Ab is fairly specific but not very sensitive for EBV infection, being present in 80% of infected teens and adults, 40% of all infected children, and 20% of infected children under 4.
Infection with EBV induces production of antibodies including IgG and IgM anti-viral capsid Ag (anti-VCA), anti-i, RF, ANA, and the Paul-Bunnell heterophile antibody. When do heterophile Ab become detectable, and for how long do they remain detectable?
? They emerge during the first week of symptoms, 3-4 wks after infection, and return to undetectable levels by 3-6 mos. ? They present in peak levels 2-6 wks after primary infection, and they may remain positive in low levels for up to a year.
What conditions can give a false positive Monospot test?
Toxoplasmosis, rubella, CMV, HIV, SLE, RA, lymphoma/leukemia.
What are the serologic markers for EBV? Do they have good sensitivity and specificity?
IgG and IgM anti-viral capsid antigen (anti-VCA). IgG anti-EBV early antigen (EBV-EA). IgG anti-EBV nuclear antigen (EBNA). These have very high sensitivity (>94%) and specificity (>95%) for EBV infectious mononucleosis.
What is the pattern of EBV serologic tests in primary infection?
Following infection, the first marker to appear is IgM anti-VCA. IgG anti-VCA emerges shortly after the IgM and slightly before the heterophile antibody. IgG anti-EA and IgG anti-EBNA begin to appear 1 to 2 months into infection. IgG anti-EBNA and IgG anti-VCA persist indefinitely.
For the EBV infectious stages (early acute, acute, convalescent, and remote), give the positivity and negativity for: heterophile Ab, IgM anti-VCA, IgG anti-VCA, IgG anti-EA, IgG anti-EBNA.
Early acute: -/+, +, +, -, -. Acute: +/-, +, +, +, -/+. Convalescent: -, -, +, +, +. Remote: -, -, -/+, +, +.
In EBV infection, IgG antibodies to early antigen (IgG anti-EA) are present at the onset of clinical illness. What are the two subsets of EA IgG?
There are two subsets of EA IgG: anti-D and anti-R. The presence of anti-D antibodies is consistent with recent infection since titers disappear after recovery, but their absence does not exclude acute illness because the antibodies are not expressed in a significant number of patients. Anti-R antibodies are only occasionally present in IM.
What is the EBER immunostain?
EBV-encoded RNA; nuclear RNA portions of EBER 1 and 2 genes. Nuclear stain.
How do the EBER and LMP1 immunostains stain Hodgkin lymphoma?
EBER is located to the nuclei of RS/H cells, with little to no expression in the background small lymphocytes. LMP1 is expressed in the cytoplasm and surface membrane of RS/H cells but is rarely expressed in latently infected background lymphocytes of Hodgkin lymphoma.
What are Digoxin-Like Immunoreactive Substances (DLIS) / Endogenous Digoxin-Like Substances (EDLS)?
They are endogenous or exogenous substances that cross-react with antidigoxin antibodies and falsely elevate serum digoxin concentrations, interfering in interpretation of results for therapeutic digoxin monitoring. Falsely lower digoxin values due to the presence of DLISs have been reported as well.
Digoxin-Like Immunoreactive Substances (DLIS) / Endogenous Digoxin-Like Substances (EDLS) are endogenous or exogenous substances that cross-react with antidigoxin antibodies and falsely elevate serum digoxin concentrations, interfering in interpretation of results for therapeutic digoxin monitoring. In what populations/conditions is it seen?
Elevated DLIS concentrations are encountered in patients with volume-expanded conditions such as uremia, essential hypertension, liver disease, and preeclampsia. They are also seen in neonates, pregnant women, and renal failure.
What drugs are identified as definitely causing drug-induced lupus?
Procainamide, hydralazine, minocycline, diltiazem, penicillamine, isoniazid (INH), quinidine, anti-tumor necrosis factor (TNF) alpha therapy (most commonly with infliximab and etanercept), interferon-alfa, methyldopa, chlorpromazine, and practolol.
Is the most common cause of the pulmonary-renal vasculitic syndrome ANCA disease or anti-GBM disease?
ANCA disease accounts for ~55% of cases, anti-GBM for 7%, and both ANCA and anti-GBM present in 8% of cases.
In the past, polyarteritis nodosa and what is now termed microscopic polyangiitis were used synonymously. What are the current definitions according to the Chapel Hill nomenclature system?
PAN is defined as an “ANCA-negative” necrotizing arteritis without immune complex deposits that primarily affects medium-sized arteries. Microscopic polyangiitis is defined as a (commonly) ANCA-positive necrotizing vasculitis without immune deposits that affects small vessels including capillaries.
What are the 3 major ANCA-associated, necrotizing small vessel vasculitides not associated with the deposition of immune complex deposits?
Wegener’s granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome.
The 3 major ANCA-associated, necrotizing small vessel vasculitides not associated with the deposition of immune complex deposits are Wegener’s granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome. How are these 3 differentiated?
Clinical features. Patient’s lacking signs of asthma, lung and sinus inflammation, or peripheral blood eosinophilia are best classified as having microscopic polyangiitis. Necrotizing inflammatory lesions involving the lungs, nasal sinuses and kidneys are typically seen in cases of Wegener’s granulomatosis. Peripheral blood eosinophilia and asthma are defining features of Churg-Strauss syndrome.
What are the 2 types of ANCA assays used?
Indirect immunofluorescence assay (IIA), using alcohol fixed buffy coat leukocytes, and enzyme-linked immunosorbent assay (ELISA), using purified specific antigens. The IIA is more sensitive and the ELISA more specific. The optimal approach to clinical testing for ANCA is therefore to screen with IIF assays, if available, and to confirm all positive results with ELISAs directed against the vasculitis-specific target antigens (PR3 and MPO).
In vasculitis, the two relevant target antigens are proteinase 3 (PR3) and myeloperoxidase (MPO). Where are these antigens located?
Both PR3 and MPO are located in the azurophilic granules of neutrophils and the peroxidase-positive lysosomes of monocytes. Antibodies with target specificities for PR3 and MPO are called PR3-ANCA (c-ANCA) and MPO-ANCA (p-ANCA), respectively.
In generalized granulomatosis with polyangiitis (GPA) (Wegener’s granulomatosis), what % of patients are ANCA positive? And what type of ANCA do they have?
~90% of patients with active, generalized GPA are ANCA-positive. There is a small subset of patients with active, generalized GPA who do not have ANCA. Furthermore, in limited forms of the disease (such as subsets in which upper respiratory tract disease predominates and renal involvement is absent), up to 40% of patients may be ANCA-negative. Thus, the absence of ANCA does not exclude the diagnosis of GPA. Among GPA patients with ANCA, 80-90% have PR3-ANCA.
In Churg-Strauss syndrome, what % of patients are ANCA positive? And what type of ANCA do they have?
~50% of CSS patients overall are ANCA positive, with the percentage being somewhat higher in those with active, untreated disease. There appears to be a moderate predilection for MPO-ANCA among those patients with CSS who have ANCA.
In microscopic polyangiitis, what % of patients are ANCA positive? And what type of ANCA do they have?
~70% of patients with MPA are ANCA positive. Most ANCA-positive MPA patients have MPO-ANCA.
~90% of patients with active generalized granulomatosis with polyangiitis (GPA) (Wegener’s granulomatosis) are ANCA-positive, and ~70% of patients with microscopic polyangiitis are ANCA positive. Can the type of ANCA (PR3-ANCA/c-ANCA or MPO-ANCA/p-ANCA) distinguish the 2 diseases?
Among GPA patients with ANCA, 80-90% have PR3-ANCA. This is in contrast to microscopic polyangiitis, where the majority of patients have MPO-ANCA. But, the 2 diseases cannot be distinguished based on ANCA specificity.
A negative ANCA assay does not rule out a vasculitis. On the other hand, elevated ANCA titers (often p-ANCA and generally low titer levels) have also been reported in many inflammatory conditions such as ___. ANCA positivity is seen in __% of patients with UC and PSC, and in __% of patients with Crohn’s disease.
A negative ANCA assay does not rule out a vasculitis. On the other hand, elevated ANCA titers (often p-ANCA and generally low titer levels) have also been reported in many inflammatory conditions such as RA, SLE, Sjogren’s syndrome, scleroderma and antiphospholipid syndrome. ANCA positivity is seen in 60-80% of patients with UC and PSC, and in 10-30% of patients with Crohn’s disease. Elevated ANCA titers can also be found in some healthy individuals.
What are some extrahepatic manifestations of HCV infection?
Hematologic diseases such as essential mixed cryoglobulinemia, lymphoma, and aplastic anemia. Renal disease, particularly membranoproliferative glomerulonephritis. Autoimmune disorders such as thyroiditis and the presence of autoantibodies. Dermatologic conditions such as porphyria cutanea tarda and lichen planus. Diabetes mellitus.
The classic ch-Aldrich syndrome phenotype includes what 3 characteristics?
Thrombocytopenia. Eczema. Recurrent bacterial, viral, and fungal infections (susceptibility to infections associated with adaptive and innate immune deficiency).
In Hashimoto’s disease, __% have anti-thyroglobulin Ab and __% have anti-thyroid peroxidase Ab. In Graves disease, __% have anti-thyroglobulin Ab and __% have anti-thyroid peroxidase Ab.
In Hashimoto’s disease, 90% have anti-thyroglobulin Ab and 95% have anti-thyroid peroxidase Ab. In Graves disease, 50% have anti-thyroglobulin Ab and 90% have anti-thyroid peroxidase Ab.
When can anti-insulin antibodies be seen?
Anti-insulin Abs can be raised in response to exogenous insulin, but this is rare in the era of human (recombinant?) insulin administration. Anti-insulin Abs may rarely occur in patients never exposed to exogenous insulin, and may cause reactive hypoglycemia (autoimmune insulin syndrome). Also, anti-insulin Abs may be found rarely in patients with insulinoma.
Do anti-insulin receptor antibodies cause hypoglycemia or hyperglycemia?
Hyperglycemia more commonly than hypoglycemia.
List causes of hypoglycemia.
Insulinoma. Nesidioblastosis. ILGF-like hormone secreting tumors (sarcomas, HCC). Advanced malignancy. Anti-insulin receptor antibodies. Autoimmune insulin syndrome. Post-gastric surgery. Drug induced (insulin, sulfonylureas, alcohol, quinine, salicylates, haloperidol, beta blockers, quinolones, pentamidine, ACE inhibitors, IGF-1). Critical illness such as hepatic/renal/cardiac failure, sepsis, inanition (def: an exhausted condition resulting from lack of food and water or a defect in assimilation; starvation). Hormone deficiency (cortisol, glucagon and epinephrine in insulin-deficient DM). Inborn errors of metabolism (glycogen storage disease, hereditary fructose intolerance, galactosemia, carnitine deficiency). Starvation. Accidental, surreptitious, or malicious hypoglycemia.
Autoantibodies can be frequently detected in type 1 diabetes. What are some targets?
Insulin. Islet cells. Glutamic acid decarboxylase (GAD65). ZnT8 (zinc transporter of islet beta cells). Insulinoma-associated protein 2 (IA-2 and IA-2 beta).
A single immunoglobulin molecule consists of 4 chains bound together by disulfide bonds: 2 heavy chains and 2 light chains. How many domains do the light chains and heavy chains have?
Light chains have 2 domains: 1 variable and 1 constant. Heavy chains have 4 to 5 domains: 1 variable and 3 to 4 constants. The terminal constant region may insert into the membrane of B cells, or, if free in serum, is called the Fc portion.
Genes for light chains are found on chromosome __ and __. Genes for heavy chains are found on chromosome __.
Genes for light chains are found on chromosome 2 (kappa) and 22 (lambda). Genes for heavy chains are found on chromosome 14 (gamma, alpha, mu, delta, eta).
There are 5 Ig classes based on the heavy chain isotype: IgG, IgA, IgM, IgD, and IgE. Which ones have subclasses, and what are they?
IgG has 4 subclasses: IgG1, IgG2, IgG3, IgG4. IgA has 2 subclasses: IgA1, IgA2.
There are 4 subclasses of IgG: IgG1, IgG2, IgG3, IgG4. Which one cannot cross the placenta? Which one cannot activate complement?
IgG2 cannot cross the placenta. IgG4 cannot activate complement.
There are 5 Ig classes based on the heavy chain isotype: IgG, IgA, IgM, IgD, and IgE. In what forms are they found in blood?
IgG - monomers (2 binding sites). IgA - dimers (4 binding sites). IgM - pentamers (10 binding sites). IgD - bound to B cells. IgE - bound to mast cells.
There are 5 Ig classes based on the heavy chain isotype: IgG, IgA, IgM, IgD, and IgE. Which ones can activate complement, and which pathway?
IgG and IgM activate the classical pathway. IgA activates the alternate pathway. IgD and IgE cannot activate complement.
There are 5 Ig classes based on the heavy chain isotype: IgG, IgA, IgM, IgD, and IgE. What immunopathogenic reactions do each produce?
IgG - immune complex (type III). IgA - immune complex, rarely. IgM - cytotoxic (type II). IgD - none. IgE - immediate-type hypersensitivity/allergic (type I).
T helper cells, T suppressor cells, and T cytotoxic cells. Which bear CD4, and which bear CD8?
T helper cells bear CD4. T suppressor cells and T cytotoxic cells bear CD8.
CD4+ T helper cells and CD8+ cytotoxic cells. Which is class I MHC restricted, and which is class II MHC restricted?
CD4+ helper cells must be presented antigen in conjunction with class II MHC molecules (they are class II MHC restricted). CD8+ cytotoxic cells must be presented antigen in conjunction with class I MHC molecules (they are class I MHC restricted).
Like immunoglobulins, T cell receptors get the variability in the variable domains from the randomness built into the rearrangement of the V, D, aand J segments of the variable region gene. But there is an additional degree of variability created by what enzyme?
There is an additional degree of variability created by the terminal deoxynucleotidyl transferase (TDT) enzyme which randomly adds nucleotides into the gene.
Over 95% of T cells have TCR alpha-beta. A small percentage of TCRs composed of gamma and delta subunits. These are found in greatest number in what body locations?
Mucosal surfaces and skin.
T cell receptors are expressed in noncovalent association with the CD__ molecule, which assists with transmembrane signaling when an antigen binds to the TCR.
T cell receptors are expressed in noncovalent association with the CD3 molecule, which assists with transmembrane signaling when an antigen binds to the TCR.
NK cells represent about 10% of peripheral blood lymphocytes. They are a subset of lymphocytic cells that bear neither the TCR or Ig; their TCR and Ig genes are in the germline (nonrearranged) state. NK cells express CD16, CD56, and CD57. What is CD16 the receptor for?
CD16 is the receptor for the Fc portion of gamma heavy chains. Through binding of opsonized cells with this receptor, they mediate antigen-dependent cellular cytotoxicity (ADCC); through this mechanism they are instrumental in combating viral infection and tumor cells.
All antigen presenting cells share phagocytic properties and certain cell antigens, such as what?
MHC class II antigens, CD68 (KP-1), and lysozyme. Antigens that are internalized by phagocytosis are processed and presented on the cell surface in association with MHC molecules. T cell stimulation and therefore stimulation of the remaining immune system begins with this. APCs also secrete IL-1.
IL-5, secreted by T cells, specifically stimulates the terminal differentiation release of eosinophils. A sub-subset of CD4+ T cells called Th2 cells stimulates both the production of IgE (secrete IL-__) and eosinophilic infiltration (secrete IL-5), particularly in the setting of parasitic infections.
IL-5, secreted by T cells, specifically stimulates the terminal differentiation release of eosinophils. A sub-subset of CD4+ T cells called Th2 cells stimulates both the production of IgE (secrete IL-4) and eosinophilic infiltration (secrete IL-5), particularly in the setting of parasitic infections.
What is the C3 convertase of the classic complement pathway and alternative complement pathway? What is the C5 convertase of the classic complement pathway and alternative complement pathway?
C3 convertase of the classic complement pathway = C4b2b. C3 convertase of the alternative complement pathway = C3bBb. C5 convertase of the classic complement pathway = C4b2b3b. C5 convertase of the alternative complement pathway = C3bBb3b.
All 3 pathways of complement activation (classical, alternative, and lectin pathways) result in the formation of activated C3b, which go on to form C5 convertases. What components produce the complement pathway effects of inflammation, opsonization, and membrane attack?
C3a and C5a (and C4a?) are anaphylatoxins, causing increased vascular permeability and promoting vasodilation and chemotaxis. C3b and C4b are opsonins. C5b6789 forms the membrane attack complex.
What is the “C3 tick over” phenomenon?
A small amount of autoactivated C3 is always present (so-called “C3 tick over” termed C3i or C3(H2O)) due to the presence of a labile thioester bond. C3 tick over is a mechanism by which the complement system monitors and probes the environment. The process is rapidly stopped on healthy human cells, but amplification may occur on foreign or damaged cells. The alternative pathway is engaged when this activated C3 binds factor B.
Human leukocyte antigen proteins are encoded by genes located within the major histocompatibility complex. The MHC complex is separated into MHC class I, class II, and class III genes which are located sequentially on chromosome ___. Also embedded in the MHC region are the genes for hereditary hemochromatosis, 21-hydroxylase, and tumor necrosis factor. These and the MHC genes are such closely linked loci that they are inherited en bloc from each parent, with no crossing over.
Human leukocyte antigen proteins are encoded by genes located within the major histocompatibility complex. The MHC complex is separated into MHC class I, class II, and class III genes which are located sequentially on chromosome 6p. Also embedded in the MHC region are the genes for hereditary hemochromatosis, 21-hydroxylase, and tumor necrosis factor. These and the MHC genes are such closely linked loci that they are inherited en bloc from each parent, with no crossing over.
On what cells are MHC class I and class II antigens expressed?
Class I antigens are found on nearly all nucleated cells and platelets (minimal to absent expression on RBCs). Class II antigens are found on macrophages, B cells, and activated T cells.
HLAs corresponding to MHC class I (__, __, and __) present peptides from inside the cell (including viral peptides if present). HLAs corresponding to MHC class II (__, __, __, __, __, and __) present antigens from outside of the cell to T-lymphocytes. HLAs corresponding to MHC class III encode components of the complement system.
HLAs corresponding to MHC class I (A, B, and C) present peptides from inside the cell (including viral peptides if present). HLAs corresponding to MHC class II (DP, DQ, DR, DM, DOA, and DOB) present antigens from outside of the cell to T-lymphocytes. HLAs corresponding to MHC class III encode components of the complement system.
What are the 3 major and 3 minor MHC class I genes in HLA? What protein binds with major and minor gene subunits to produce a heterodimer?
The 3 major genes: HLA-A, HLA-B, HLA-C. The 3 minor genes: HLA-E, HLA-F, HLA-G. Beta2-microglobulin binds with major and minor gene subunits to produce a heterodimer.
Describe HLA nomenclature.
Modern HLA alleles are typically noted with a variety of levels of detail. Most designations begin with HLA- and the locus name, then * and some (even) number of digits specifying the allele. The first two digits specify a group of alleles. Older typing methodologies often could not completely distinguish alleles and so stopped at this level. The third through fourth digits specify a synonymous allele. Digits five through six denote any synonymous mutations within the coding frame of the gene. The seventh and eighth digits distinguish mutations outside the coding region. Letters such as L, N, Q, or S may follow an allele’s designation to specify an expression level or other non-genomic data known about it. Thus, a completely described allele may be up to 9 digits long, not including the HLA-prefix and locus notation.
Since each MHC complex is closely linked and inherited en bloc, each parental chromosome can be thought of as a haplotype. Thus, the chance that 2 siblings are HLA-identical is essentially __%.
Since each MHC complex is closely linked and inherited en bloc, each parental chromosome can be thought of as a haplotype. Thus, the chance that 2 siblings are HLA-identical is essentially 25%. The chance of having an HLA-identical sibling goes up with the number of siblings: with 1 sibling, the chance is 25%, with 2 it is around 45%, and with 3 it is nearly 60%.
For deficiencies in B cells/immunoglobulins, T cells, phagocytes, and terminal complement, what types of infections are seen?
B cells/immunoglobulins - recurrent bacterial infections. T cells - viral and fungal infections. Phagocytes - Staphylococci. Terminal complement - encapsulated organisms (such as S. pneumoniae or N. meningitidis).
Is an absolute lymphopenia more common in B cell immune defects or T cell immune defects?
Absolute lymphopenia is uncommon in B defects but common in T cell defects.
What role does HLA testing have in the evaluation of immunodeficiency?
HLA testing does not normally have a role in the evaluation of immunodeficiency. It may be undertaken in other scenarios: pre transplantation compatibility testing, platelet refractoriness, paternity/forensic identity testing, and the evaluation of several HLA-linked autoimmune disorders.
What is the microlymphocytotoxicity assay?
The test detects either HLA antigens or antibodies. For Ag typing, it is best at detecting class I Ags (another technique, especially a DNA-based method, is preferred for detecting class II). For detecting Ags, HLA antisera are incubated with pt lymphocytes enriched from peripheral blood in the presence of excess complement, followed by the addition of dye. Microscopic examination shows either intact lymphs (a negative reaction) or damaged lymphs that internalize the dye (a positive reaction). For detecting Abs, pt serum is incubated with lymphs of known HLA type, and a similar procedure is carried out. The pt’s serum can be run against a panel of known lymph to determine the panel reactive antibody (PRA) level.
What is the mixed lymphocyte culture assay?
This test detects HLA class I (HLA-D) differences between a potential donor and recipient. After a B cell enrichment step (since class II molecules are numerous on B cells but not resting T cells), prospective donor and recipient B cells are cultured together. They proliferate if stimulated by one another’s HLA dissimilarities. At the end of the incubation period, the assay is pulsed with radioactive thymidine to determine the extent of DNA synthesis, a reflection of the amount of proliferation and thus the amount of incompatibility. By first subjecting the donor lymphocytes to irradiation (rendering them incapable of proliferation), the reaction can be made more specific for recipient intolerance of the potential donor.
In organ transplantation, ABO compatibility is most important, followed by HLA class ___ compatibility.
In organ transplantation, ABO compatibility is most important, followed by HLA class II compatibility.
Evaluation of HLA by serology vs. direct DNA testing (PCR).
PCR has the advantage of eliminating many of the biologic uncertainties of the serologic techniques such as microlymphocytotoxicity and mixed lymphocyte culture assays. Furthermore, it can resolve HLA types with much greater specificity than the serologic techniques. The DNA is usually obtained from peripheral blood.
What PCR techniques can be used for HLA typing?
Primers can be used that either amplify the locus of interest (regardless of its allele) for additional study; alternatively, primers may be used that will amplify the locus only if a specific allele is present - if a band results from this latter amplification, then that genotype is confirmed. In the former amplification, sequence-specific oligonucleotides can be applied to the amplified DNA to determine the identity of the alleles. For example, if looking for HLA-B27, the pt’s HLA-B locus can first be nonspecifically amplified then treated with HLA-B27-specific oligonucleotide probe to see if hybridization occurs. Alternatively, HLA-B27-specific primer sequences can be used in the amplification step; the presence of an identifiable band after PCR confirms HLA-B27. Also, an unknown allele can be directly sequenced and compared to known sequences.
HLA matching for transplantation usually involves at least what 3 loci?
HLA-A, HLA-B, and HLA-DR.
In HLA matching for transplantation, why is an in vitro assessment of compatibility (a crossmatch) still necessary when there appears to be a perfect 6 of 6 match?
HLA matching for transplantation usually involves at least 3 loci: HLA-A, HLA-B, and HLA-DR. Since each person has 2 alleles (one on each 6p) for each locus, there are 6 possible alleles. The potential recipient may have been sensitized to these and other not-normally-tested alleles through pregnancy or transfusion, so a crossmatch is still necessary. The lymphocyte crossmatch can detect pre-existing HLA allo-antibodies in the serum of the potential recipient that have specificity for HLA antigens in the potential donor. These HLA antibodies are the mediators of hyper acute rejection.
Transplantation crossmatch is usually performed by incubating donor (lymphocytes/serum) with recipient (lymphocytes/serum) in the presence of excess complement.
Transplantation crossmatch is usually performed by incubating donor lymphocytes with recipient serum in the presence of excess complement. An auto-crossmatch is performed to control for auto-antibodies (which do not appear to impact transplant survival).
For (organ) transplantation, one seeks ABO-compatible, HLA-matched (6 of 6 ideally), and crossmatch-compatible donor and recipient. Similar requirements are made for (organ) and (organ) transplants. For other organs, such as (organ) and (organ), such stringency is not required, and ABO-compatibility is the main concern.
For renal transplantation, one seeks ABO-compatible, HLA-matched (6 of 6 ideally), and crossmatch-compatible donor and recipient. Similar requirements are made for marrow and progenitor cell transplants. For other organs, such as heart and lung, such stringency is not required, and ABO-compatibility is the main concern.
A poor reaction (weak response to/low antibody titers developing against antigen) to carbohydrate antigens (such as pneumococcal vaccine, meningococcal vaccine, or ABO antigens), indicates a purely (B cell/T cell) defect.
A poor reaction (weak response to/low antibody titers developing against antigen) to carbohydrate antigens (such as pneumococcal vaccine, meningococcal vaccine, or ABO antigens), indicates a purely B cell defect. Antibodies raised to protein antigens require orchestration of B cell and T cell function.
What conditions are associated with high IgE levels?
Parasitic infection. Churg-Strauss syndrome. Hyper-IgE (Job) syndrome. IgE myeloma. Hodgkin lymphoma. IgE is not uniformly elevated in allergic states so is not a useful screening test in that setting.
