Immunology Flashcards
What is a Type I hypersensitivity reaction?
Mechanism: IgE mediated
Clinical Symptoms: urticaria, angioedema, anaphylaxis, anaphylactic shock, bronchial asthma, rhinitis, eczema
What is a Type II hypersensitivity reaction?
Mechanism: IgG-mediated cytotoxic hypersensitivity (i.e. antibody mediated)
Clinical symptoms: Autoimmune haemolytic anaemia, thrombocytopenia, blood transfusion reactions; bullous pemphigoid
What is a Type III hypersensitivity reaction?
Mechanism: immune complex mediated hypersensitivity; Ag-Ab complexes deposit and induce complement / inflammatory/ neutrophil response
Clinical symptoms: Vasculitis, GN, Organ specific reactions; SLE
What is a Type IV hypersensitivity reaction?
Mechanism: T cell-mediated hypersensitivity
Th1 cells activate macrophages or Tc cells
Clinical symptoms: SJS; TEN; DRESS; fixed drug eruption; contact dermatitis; delayed urticaria; MS; Scabies; GVHD; TB skin reaction
What is the function of IL-1?
Central regulator of the inflammatory response
Proliferation of activated T cells, B cells
Produced by macrophages, dendritic cells
What is the function of IL-2?
Produced by T cells
Growth of activated T and B cells
Activation of NK cells
What is the function of IL-3?
Produced by T cells, macrophages
Mast cell growth
Growth and differentiation of haematopoetic precursors
What is the function of IL-4?
Produced by T and B cells, macrophages, mast cells and basophils
Activation of B cells to promote IgE switching
Differentiation of Th2 cells
What is the role of IL-5?
Produced by Th2 subset, mast cells
IgM, IgA production
Driver ofWCC differentiation to eosinophilic pathway
Activated B cell proliferation
What is the function of IL-6?
Produced by T cells, macrophages, monocytes
Production of acute phase proteins
Growth and differentiation of haemopoetic cells
FEVER
What is the role of IL-8?
Produced by T cells, monocytes and neutrophils
Activation of Neutrophils
What is the function of IL-10?
Produced by T and B cells, macrophages
Suppression of macrophage functions & Th1 cells
Activation of B cells
What is the function of IL-17?
Produced by CD4 T cells, ILC3, NK cells
Promotes inflammation by increasing production of pro inflammatory cytokines (IL-1, IL-6, TNF alpha, G-CSF, GM-CSF) by epithelial, endothelial & fibroblast cells
IL-17 Deficiency = Job Syndrome
What is the function of TNF alpha?
Produced by macrophages, lymphocytes, neutrophils, eosinophils, NK cells
Activates macrophages, granulocytes, cytotoxic cells and endothelium
Enhanced HLA class I expression
Stimulation of acute phase response
Anti-Tumor effects
What is the function of TNF beta?
Produced by CD4 T cells Acute phase proteins Anti viral / anti parasite activity Activation of phagocytes Induce pro inflammatory cytokines
General function of Tumor Necrosis Factor?
Transmembrane protein - can be cleaved and released to act as a cytokine
Principle mediator of response to gram negative bacteria
What is the function of IFN-alpha?
Produced by leukocytes
Antiviral; up-regulates MHC Class I
What is the role of IFN-gamma?
Antiviral macrophage activation
Enhance HLA class I and class II expression
Characterises Th1 cells
Suppression of Th2 cells
Antagonises IL-4 effect
Stimulation of macrophages and endothelium
Aberrant IFN-gamma expression is associated with a number of auto inflammatory and auto immune conditions e.g. MS
What is BAFF?
B-cell-activating factor Member of of the TNF family Cytokine that promotes B cell maturation, proliferation and survival Survival factor for B cells Induced by interferon type 1 and type 2 Co-stimulates immune B cell responses
What is BLyS?
B lymphocyte stimulator
Soluble ligand of the TNF cytokine family
Role in B cell differentiation, homeostasis and selection
BLyS levels affect survival signals and selective apoptosis of auto-antibody producing B cells
What is VEGF?
Vascular Endothelial Growth Factor
Expressed on endothelial and non endothelial cells including tumor cells
Potent angiogenic factor
Investigations in Common Variable Immunodeficiency (CVID)
IgG low - one or both of IgA/IgM also decreased
B cell count nor
Impaired vaccination response
Low switched memory B cells
Investigations in X-linked (Bruton’s) Agammaglobulinaemia
IgG levels - typically undetectable B-cell count - zero No plasma cells or germinal centres in tissue biopsies B-cell precursors present in the marrow BTK expression in flow cytometry Genetic analysis of BTK gene
Northern blotting is used for?
Detect RNA
SNOW - South - NOrth - West
DROP - DNA - RNA - Protein
Abacavir - HLA hypersensitivity
HLA-B*57:01
A derivative of abacavir binds to B57:01 within the cell - alters the repertoire of self peptides which can bind to B57:01. Presentation of altered self peptides to T cells = altered immune response
Carbamazepine - HLA hypersensitivity
HLAB*15:02
What is the role of the HLA / MHC in the immune response?
Presentation of antigens to T cells
Extracellular proteins (mainly bacteria) are processed through phagocytosis, phagolysomes onto MHC II = CD4+ T cells
Cytosine proteins made by the cell are processed via the golgi onto MHC I = CD8+ T cells (mainly viral response)
Distribution of HLA / MHC?
MHC I - present on membrane of all nucleated cells (except RBCs)
MHC II - present on APCs: dendritic cells, B cells and macrophages
What is the main purpose of somatic hypermutation in B cells?
Selection of high affinity B cells
Absence of B cells is characteristic of which primary disorder?
X-linked agammaglobulinaemia (XLA)
Immunoglobulins are produced by plasma cells, which themselves are the result of the development & differentiation of B cells
Which disease is caused by decreased apoptosis resulting in increased presentation of self antigen?
SLE
The mediators of SLE are autoantibodies and the immune complexes they form with antigens
Cancers related to Common Variable Immunodeficiency Disease (CVID)
Non-Hodgkins lymphomas
Cancer’s related to Hyper-IgE syndrome (Job’s syndrome)
Aggressive B cell lymphomas
May be linked to abnormalities in STAT3 / IL-21 dependent differentiation of B cells
Activation of classical complement pathway?
Binding of C1q in the C1 complex to the Fc portion of IgG or IgM immune complexes
Activation of the leptin complement pathway?
Mannose-binding lectin binding to sugar moieties on the surface of pathogens leading to the engagement of proteases (analogous to Cr1 and C1s of the classical pathway)
Activation of alternative complement pathway?
Does not require antibody or contact with a microbe to become activated. C3 is constantly autoactivated at a low level, a process that is rapidly amplified in the presence of a microbe / damaged host cell / lack of a complement regulatory protein
Goal of the 3 complement cascades?
Deposition of C3b on a target (opsonisation), which marks it for elimination
Also leads to the release of pro inflammatory anaphylatoxins (C3a and C5a) and assembly of the membrane attack complex (MAC)
Diseases associated with deficiencies in C3-C9
Pneumococcal & influenza - C3 deficiency
Neisserial infections - C5, C6, C7, C8 or C9 deficiency
3 stages of Tcell development
- Migration to thymus
- T cell receptor gene rearrangement
- Selection = learn to respond to MHC
Selection of T cells
Need to be useful: positive selection - choose T cells that can interact with MHC
Can’t be useless: death by neglect - ignore T cells that cannot interact with MHC
Can’t be harmful: negative selection - delete self reactive T cells
Turn harmful to useful: induce Treg cells from self reactive T cells
3 signal model of T cell activation
Signal 1: Ag peptides presented by MHC
Signal 2: co-stimulation (CD40 / 80 / 86)
Signal 3: Th subset preference (Th 1 / Th2 / Th17 / Treg)
What is the critical step in central T cell tolerance?
Negative selection
Role of AIRE?
AIRE is a transcription factor expressed in the medullary of the thymus
Is part of the mechanism which eliminates self reactive T cells - i.e. drives negative selection
Recurrent infection suggestive of a T cell immunodeficiency?
Intracellular organism infections
- Fungi e.g. mucosal candida, pneumonitis
- viruses e.g. CMV, VZV, HSV, Protozoa (CD8)
- Listeria