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Flashcards in Midterm Deck (69):
1

A vaccine is a product that produces immunity from a disease and can be administered through needle injections, by mouth, or by aerosol. The following properties render a substance immunogenic:
a. high molecular weight
b. chemical complexity
c. sufficient stability and persistence after injection
d. all of the above
e. all of the above are essential but not sufficient

e. all of the above are essential but not sufficient

2

Smallpox vaccine, the first successful vaccine to be developed, was introduced by Edward Jenner in 1796. He followed up his observation that milkmaids who had previously caught cowpox did not later catch smallpox by showing that inoculated cowpox protected against inoculated smallpox. The protection against smallpox afforded by prior infection with cowpox represents
a. antigenic specificity
b. antigenic cross-reactivity
c. enhanced viral uptake by macrophages
d. innate immunity
e. passive protection

b. antigenic cross-reactivity

3

A 22-year-old man was treated for acute myeloid leukemia (AML) with cyclical combination chemotherapy, and complete clinical remission was obtained after three courses. However, remission in AML is generally short; half the patients relapse within a year and second remissions are difficult to achieve. Bone marrow transplantation after high-dose chemoradiotherapy is therefore considered in young patients with suitable family members. Which of the following does not apply to bone marrow as a primary lymphoid organ?
a. cellular proliferation
b. differentiation of lymphocytes
c. cellular interaction
d. antigen-dependent response
e. none of the above

d. antigen-dependent response

4

Lymph nodes are tiny, bean‐shaped organs that filter lymph fluid. They are located throughout the body, but particular collections are found just under the skin in the neck, under the arms, and in the groin area. Lymph nodes are part of the lymphatic system, which is one of the body's defense mechanisms against the spread of infection and cancer. Which of the following apply uniquely to secondary lymphoid organs?
A. presence of precursor B and T cells
B. circulation of lymphocytes
C. terminal differentiation
D. cellular proliferation
E. All of the above.

C. terminal differentiation

5

To elicit an immune response, a compound must contain an antigenic determinant or epitope and must be of sufficient size to initiate lymphocyte activation necessary for an antibody response. In practice, small chemical compounds called haptens are generally not good immunogens. Which of the following is correct about properties of haptens?
A. They require carrier molecules to be immunogenic.
B. They react with specific antibodies when homologous carriers are not employed.
C. They interact with specific antibody even if the hapten is monovalent.
D. They cannot stimulate secondary antibody responses without carriers.
E. All of the above.

E. All of the above.

6

The concept of adjuvants arose in the 1920s from observations that horses that developed an abscess at the inoculation site of diphtheria toxoid generated higher specific antibody titers. What is the major property of immunologic adjuvants?
A. They reduce the toxicity of the immunogen
B. They enhance the immunogenicity of haptens
C. They enhance hematopoiesis
D. They enhance the immune response against the immunogen
E. They enhance immunologic cross‐reactivity

D. They enhance the immune response against the immunogen

7

The lymphoid system is made up of a network of lymph fluid, lymphocytes, lymph vessels, lymph nodes and the lymphatic organs. These organs are the spleen, thymus, tonsils, adenoid and bone marrow. Lymphatic tissue is also found in other parts of the body, including the stomach, intestines and skin. Which of the following is the major function of the lymphoid system?
A. innate immunity
B. inflammation
C. phagocytosis
D. acquired immunity
E. None of the above

D. acquired immunity

8

The innate immune system provides first‐line defenses in response to invading microorganisms and endogenous danger signals (damaged tissues) by triggering robust inflammatory and antimicrobial responses. Which of the following does not apply to innate immune mechanisms?
A. absence of specificity
B. activation by a stimulus
C. involvement of multiple cell types
D. a memory component

D. a memory component

9

Which of the following pairs is mismatched?
A. lymphocytes: innate immune response
B. natural killer cell: kills virus‐infected cells
C. macrophage: phagocytosis and killing of microorganisms
D. erythrocyte: oxygen transport
E. eosinophil: defense against parasites.

A. lymphocytes: innate immune response

10

White blood cells are part of the body’s immune system. They help the body fight infection and
other diseases. Types of white blood cells are granulocytes (neutrophils, eosinophils, and basophils) and mononuclear cells (monocytes and T and B lymphocytes). Checking the number of white blood cells in the blood is usually part of a complete blood cell (CBC) test. It may be used to look for conditions such as infection, inflammation, allergies, and leukemia. What is the term generally used to describe all white blood cells?
A. hematopoietic cells
B. myeloid progenitor
C. dendritic cells
D. monocytes
E. leukocytes

E. leukocytes

11

The most abundant type of leukocyte in human peripheral blood is:
A. eosinophil
B. basophil
C. neutrophil
D. monocyte
E. lymphocyte

C. neutrophil

12

A workup on an ill child revealed low levels of complement C3 in her blood. Which one of the following presentations did this child most likely manifest?
A. Chronic eczema
B. Immune hemolytic anemia
C. Incomplete recovery from viral infections
D. Poor response to vaccination
E. Recurrent infections with extracellular bacteria

E. Recurrent infections with extracellular bacteria

13

Activation of macrophages is best achieved by which cytokine?
A. Interferon gamma (IFN‐gamma)
B. Granulocyte monocyte colony‐stimulating factor (GM‐CSF)
C. Interleukin‐1
D. Macrophage chemotactic protein (MCP)
E. Transforming growth factor beta (TGF‐beta)

A. Interferon gamma (IFN‐gamma)

14

Toll‐like receptors (TLRs) are a family of homologous receptors expressed on many cell types and are involved in innate immune responses. Ten different mammalian TLRs have been identified, and several ligands for many of these receptors are known. Which of the following is a TLR ligand?
A. Single‐stranded RNA
B. Transfer RNA
C. Double‐stranded DNA
D. Unmethylated CpG DNA
E. Heterochromatin

D. Unmethylated CpG DNA

15

Which of the following is a receptor on macrophages that is specific for a structure produced by bacteria but not by mammalian cells?
a. CD36 (scavenger receptor)
b. Fc receptor
c. Complement receptor
d. Mannose receptor
e. ICAM‐1

d. Mannose receptor

16

Which one of the following cells is the major source of tumor necrosis factor alpha (TNF‐), interleukin‐1, and interleukin‐12?
a. B cells
b. Macrophages
c. Mast cells
d. Th1 cells
e. Th2 cells

b. Macrophages

17

Activation of the complement system, directly results in which one of the following outcomes?
A. Enhanced phagocytosis
B. Expression of Toll‐like receptors on phagocyte cell surface
C. Enhancement of immune‐mediated neutralization
D. Interaction of Fc receptors with antibodies bound to antigens on the pathogen cell surface
E. Proliferation of T cells

A. Enhanced phagocytosis

18

Septic shock may develop when bacterial components are recognized by macrophages. Which two proinflammatory cytokines are rapidly elevated during early phases of bacterial septic shock?
A. TNF‐α and IL‐1β
B. IL‐2 and TNF‐β
C. IL‐4 and IL‐5
D. TNF‐β, TGF‐β

A. TNF‐α and IL‐1β

19

Several of the complement components are:
A. Glycolipids
B. Cytokines
C. Enzymes
D. Hormones
E. Antibodies

C. Enzymes

20

NK cells are activated by several cytokines that are produced by specific cell types including which of the following?
A. IL‐12 which is produced by macrophages.
B. IL‐12 which is produced by virally infected cells.
C. IFN‐gamma and IFN‐beta which are produced by virally infected cells.
D. Answers A and C are correct.
E. Answers B and C are correct.

A. IL‐12 which is produced by macrophages.

21

Complement lyses cells by:
A. enzymatic digestion of the cell membrane.
B. activation of adenylate cyclase.
C. insertion of complement proteins into the cell membrane.
D. inhibition of elongation factor 2.
E. activation of TLR‐4.

C. insertion of complement proteins into the cell membrane.

22

When the innate immune system encounters a foreign antigen, what cell‐surface molecule plays the role of recognizing the presence of a foreign antigen?
A. Antibody
B. T cell receptor
C. The membrane attack complex of complement
D. HLA Class II
E. Toll‐like receptor

E. Toll‐like receptor

23

You have a patient who makes autoantibodies against his own red blood cells, leading to their hemolysis. Which one of the following mechanisms is MOST likely to explain the hemolysis?
A. Perforins from cytotoxic T cells lyse the red cells.
B. Neutrophils release proteases that lyse the red cells.
C. Interleukin‐2 binds to its receptor on the red cells, which results in lysis of the red cells.
D. Complement is activated, and membrane attack complexes lyse the red cells.

D. Complement is activated, and membrane attack complexes lyse the red cells.

24

Cells of the innate immune system are triggered by the binding of surface receptors. In general, the action taken is determined by
A. a single receptor per cell.
B. a single type of receptor found on all cells.
C. the integration of signals generated by multiple receptors on single cells.
D. multiple receptors that bind soluble ligands only.
E. nonspecific receptors capable of binding a wide array of ligands.

C. the integration of signals generated by multiple receptors on single cells.

25

Neutrophils are attracted to the sites of extracellular bacterial infections by which two important chemotactic substances?
A. Bacterial mannose and lipopolysaccharide
B. Complement C5a and interleukin‐8 (CXCL‐8)
C. Histamine and complement C3b
D. lnterleukin‐7 and interleukin‐16
E. Leukotriene B4 and granulocyte colony‐stimulating factor (G‐CSF)

B. Complement C5a and interleukin‐8 (CXCL‐8)

26

Which of the following about NK cells is correct?
A. NK cells proliferate in response to antigen
B. NK cells kill their target cells by phagocytosis and intracellular digestion
C. NK cells are a subset of polymorphonuclear cells
D. NK‐cell killing is extracellular
E. NK cells are particularly effective against certain bacteria

D. NK‐cell killing is extracellular

27

A patient is admitted to your hospital with multiple bacterial infections. He is found to have a complete absence of C3 component of complement. Which complement‐mediated function would remain intact in such a patient?
A. lysis of bacteria
B. opsonization of bacteria
C. generation of anaphylatoxins
D. generation of neutrophil chemotactic factors
E. None of the above.

E. None of the above.

28

Which of the following screening tests would be most useful for confirming a presumptive diagnosis of a complement immunodeficiency?
A. quantitation of serum opsonic activity
B. quantitation of serum hemolytic activity
C. quantitation of C3 content of serum
D. quantitation of C1 content of serum
E. electrophoretic analysis of patient's serum

B. quantitation of serum hemolytic activity

29

Complement is required for which of the following processes?
A. lysis of erythrocytes by lecithinase
B. NK‐mediated lysis of tumor cells
C. phagocytosis
D. enhancement of acute phase responses
E. All of the above

C. phagocytosis

30

Active fragments of C5 can lead to the following, except
A. contraction of smooth muscle
B. vasodilation
C. attraction of leukocytes
D. attachment of lymphocytes to macrophages

D. attachment of lymphocytes to macrophages

31

Which of the following can activate the alternative pathway of complement?
A. Lipopolysaccharides
B. Some viruses and virus‐infected cells
C. Fungal and yeast cell walls (zymosan)
D. Many strains of gram‐positive bacteria
E. All of the above.

E. All of the above.

32

Which of the following cell types use activating and inhibitory receptors for regulation of their functional activity?
A. Natural killer cells
B. Cytotoxic T lymphocytes
C. Naive B cells
D. Helper T lymphocytes
E. Memory B cells

A. Natural killer cells

33

Toll‐like receptors and other receptors are potent activators of various components of the innate immune system. All of the following proteins are expressed in response to signaling by these receptors EXCEPT:
A. Interleukin‐12
B. Myeloperoxidase
C. Tumor necrosis factor
D. Inducible nitric oxide synthase (iNOS)
E. CD28

E. CD28

34

Which of the following pathogen‐associated molecular patterns is important for activating of the innate immune system against an infection caused gram‐positive bacteria?
A. Lipoteichoic acid
B. Double‐stranded RNA
C. Lipopolysaccharide (LPS)
D. Lipoarabinomannan
E. Phosphatidylinositol dimannoside

A. Lipoteichoic acid

35

Macrophages and neutrophils express several enzymes that are involved in biochemical mechanisms that kill ingested microbes. Which of the following is NOT an enzyme expressed by these cells?
a. Inducible nitric oxide synthase (iNOS)
b. Granzyme B
c. NADPH oxidase
d. Superoxide dismutase
e. Myeloperoxidase

b. Granzyme B

36

Antibodies and T lymphocytes are the respective mediators of which two types of immunity?
A. Innate and adaptive
B. Passive and active
C. Specific and nonspecific
D. Humoral and cell‐mediated
E. Adult and neonatal

D. Humoral and cell‐mediated

37

Natural killer cells assess whether other cells are abnormal by detecting types and levels of surface‐associated
A. MHC class I molecules.
B. nonself molecules.
C. pathogen‐associated molecular patterns.
D. pattern recognition receptors.
E. somatically generated cell surface receptors.

A. MHC class I molecules.

38

The two major functional classes of effector T lymphocytes are:
A. Helper T lymphocytes and cytotoxic T lymphocytes
B. Natural killer cells and cytotoxic T lymphocytes
C. Memory T cells and effector T cells
D. Helper cells and antigen‐presenting cells
E. Cytotoxic T lymphocytes and target cells

A. Helper T lymphocytes and cytotoxic T lymphocytes

39

Which of the following cell types is required for all humoral immune responses?
A. Natural killer cells
B. Dendritic cells
C. Cytolytic T lymphocytes
D. B lymphocytes
E. Helper T lymphocytes

D. B lymphocytes

40

Immunologic memory refers to
A. activation of phagocytic cells to ingest microbial invaders.
B. changes in adaptive immune responses with subsequent encounters with antigen.
C. constancy of the response of the innate immune response to a particular microbe.
D. recognition of pathogen‐associated molecular patterns by pattern recognition receptors.
E. stimulating a defective host cell with reduced MHC I molecules to commit suicide.

B. changes in adaptive immune responses with subsequent encounters with antigen.

41

Natural killer (NK) cells lyse Epstein–Barr virus‐infected B cells with deficient MHC I expression. The NK receptors that initiate the lytic activity are
A. complement receptors.
B. Fc receptors.
C. killer activation receptors.
D. killer inhibition receptors.
E. monomeric immunoglobulin receptors

C. killer activation receptors.

42

Which type of antigen‐presenting cell is most important for activating naive T cells?
A. Macrophage
B. Dendritic cell
C. Endothelial cell
D. B lymphocyte
E. Epithelial cell

B. Dendritic cell

43

Which one of the following statements about dendritic cells is true?
A. Immature dendritic cells are ubiquitously present in skin and mucosal tissues.
B. Dendritic cell maturation occurs after migration to lymph nodes in response to signals
derived from activated T cells.
C. Class II MHC and T cell costimulators are highly expressed on immature dendritic cells and
are down‐regulated during maturation.
D. Dendritic cells that enter lymph nodes through draining lymphatics migrate to the B cell–rich
follicles in response to chemokines.
E. The principal function of mature dendritic cells is antigen capture.

A. Immature dendritic cells are ubiquitously present in skin and mucosal tissues.

44

Which of the following is the generative lymphoid organ for T lymphocytes?
A. Bone marrow
B. Spleen
C. Lymph node
D. Thymus
E. Tonsil

D. Thymus

45

Which vessels drain lymph away from a lymph node?
A. Afferent lymphatic
B. Efferent lymphatic
C. Marginal zone
D. Red pulp of spleen
E. White pulp of spleen

B. Efferent lymphatic

46

Where do Langerhans cells reside?
A. Red pulp of spleen
B. White pulp of spleen
C. Epidermis
D. Dermis
E. Peyer’s patch

C. Epidermis

47

What is the most abundant Ig isotype in the blood?
A. IgA
B. IgD
C. IgE
D. IgG
E. IgM

D. IgG

48

Which secreted form of Ig isotype forms pentamer around a J chain?
A. IgA
B. IgD
C. IgE
D. IgG
E. IgM

E. IgM

49

Which Ig isotype is closely associated with immediate hypersensitivity (allergic) disease?
A. IgA
B. IgD
C. IgE
D. IgG
E. IgM

C. IgE

50

What is a proteolytic fragment of an antibody molecule that contains one intact antigen‐ binding site?
A. Linear determinant
B. Hinge region
C. Fab
D. Fc
E. Hapten

C. Fab

51

What is the proteolytic fragment of an antibody molecule that contains the heavy chain constant region?
A. Conformational determinant
B. Linear determinant
C. Neoantigenic determinant
D. Hinge region
E. Fc

E. Fc

52

Which of the following statements about cell‐mediated immunity (CMI) is NOT true?
A. Deficiencies in CMI result in susceptibility to infections by viruses and intracellular bacteria.
B. CMI can be adoptively transferred by injecting serum from one individual to another.
C. Delayed‐type hypersensitivity (DTH) is not a protective response against intracellular bacteria such as Mycobacterium tuberculosis.
D. The principal form of CMI that protects against viral infections is mediated by CD8+ cytolytic T lymphocytes.
E. Phagocytes are essential in the effector phase of CMI responses to bacteria such as Listeria monocytogenes.

B. CMI can be adoptively transferred by injecting serum from one individual to another.

53

The induction phase of a cell‐mediated immune response includes which of the following events?
A. CD4+ T cell secretion of interferon‐ leading to macrophage activation
B. CD8+ T cell lysis of a virally infected cell
C. Clonal expansion of CD8+ T cells within a lymph node
D. Migration of CD4+ effector T cells from blood vessels into a tissue site of infection
E. Migration of a naive CD4+ T cell from the thymic medulla into the circulation

C. Clonal expansion of CD8+ T cells within a lymph node

54

Anti‐tumor necrosis factor (TNF) antibodies are now used in the treatment of patients with rheumatoid arthritis. A complication of this therapy, seen in a subset of patients, is infections with various microorganisms, including bacteria and fungi. Which of the following is a function of TNF that is important in the defense against infections and is likely to be impaired in the setting of TNF blockade?
A. Induction of fever
B. Reduction in cardiac output
C. Enhanced procoagulant activity of endothelial cells
D. Enhanced glucose utilization by muscle cells
E. Induction of E‐selectin expression on endothelial cells

E. Induction of E‐selectin expression on endothelial cells

55

Which of the following cell types do NOT have clonally distributed antigen receptors?
A. Natural killer cells
B. Cytotoxic T lymphocytes
C. Naive B cells
D. Helper T lymphocytes
E. Memory B cells

A. Natural killer cells

56

Which of the following statements about antibodies is NOT true?
A. They serve as membrane‐bound antigen receptors on the surface of B cells.
B. In secreted form, they serve as effector molecules that facilitate the elimination of microbes or toxins.
C. They are specific for proteins and polysaccharides exclusively.
D. They bind antigen with average higher affinity than do T cell receptors.
E. They are present in most biologic fluids in the body.

C. They are specific for proteins and polysaccharides exclusively.

57

Which portion of an antibody defines its isotype?
A. The variable regions of the light chains
B. The variable regions of the heavy chains
C. The constant regions of the heavy chains
D. The J chain
E. The complementarity‐determining regions

C. The constant regions of the heavy chains

58

When an immunoglobulin molecule is subjected to cleavage by pepsin, the product(s)
A. are individual heavy and light chains.
B. can no longer bind to antigen.
C. consist of two separated antigen‐binding fragments.
D. crystallize during storage in the cold.
E. is a dimeric antigen‐binding molecule.

E. is a dimeric antigen‐binding molecule.

59

In humans, MHC class II molecules are expressed by
A. all nucleated cells.
B. B cells, dendritic cells, and macrophages.
C. erythrocytes.
D. mast cells, basophils, and eosinophils.
E. naïve T cells, T helper cells, and CTL

B. B cells, dendritic cells, and macrophages.

60

Certain pathogens such as mycobacteria, Listeria, Leishmania, and Salmonella take up residence in macrophages and are, thereby, protected from elimination. These microorganisms can be eliminated when their host macrophages are activated and produce increased amount of nitric oxide, oxygen radicals, and other microbicidal molecules. Which of the following cytokines is the best in induction of microbial killing the cells?
A. IL‐1
B. IL‐6
C. TNF‐alpha
D. IFN‐gamma
E. TGF‐beta

D. IFN‐gamma

61

Chediak‐Higashi syndrome (CHS) is a disease causing impaired bacterial killing due to failure of phagolysosome formation. There is impaired lysosome degranulation within phagosomes, so phagocytosed bacteria are not destroyed by the lysosome's enzymes. Formation of giant granules within phagocytes is the diagnostic characteristic for CHS. Which of the following immune cells are used to diagnose CHS by microscopy?
A. T cells
B. Mast cells
C. NK cells
D. T cells
E. Neutrophils

E. Neutrophils

62

Deficiencies affecting the attachment of immune cells to blood vessel walls, cell movement, and interaction with complement fragments impair the ability of granulocytes and lymphocytes to migrate out of the intravascular compartment, to engage in cytotoxic reactions, and to phagocytose bacteria. Deficiency in which of the following molecular interactions will affect the phase of neutrophil rolling along vascular endothelium?
A. E selectin ‐‐‐ sialylated carbohydrates
B. IL‐8 ‐‐‐ IL‐8 receptor
C. MCP‐1 ‐‐‐ MCP‐1 receptor
D. beta2 integrin ‐‐‐ ICAM‐1
E. C5a ‐‐‐ C5a receptor

A. E selectin ‐‐‐ sialylated carbohydrates

63

Frequent or recurrent types of which of the following infections may strongly indicate the presence of a primary immunodeficiency disease?
A. Streptococcal pharyngitis ("strep throat")
B. Ear and sinus infections
C. Urinary tract infections
D. Viral upper respiratory tract infections

B. Ear and sinus infections

64

Deficiency in which of the following molecular interactions will affect activation of a high affinity state of neutrophil integrins?
A. E selectin ‐‐‐ sialylated carbohydrates
B. IL‐8 ‐‐‐ IL‐8R
C. MCP‐1 ‐‐‐ MCP‐1 receptor
D. beta2 integrin ‐‐‐ ICAM‐1
E. C5a ‐‐‐ C5a receptor

B. IL‐8 ‐‐‐ IL‐8R

65

Deficiency in which of the following molecular interactions will affect activation of a high affinity state of monocyte integrins?
A. E selectin ‐‐‐ sialylated carbohydrates
B. IL‐8 ‐‐‐ IL‐8R
C. MCP‐1 ‐‐‐ MCP‐1 receptor
D. beta2 integrin ‐‐‐ ICAM‐1
E. C5a ‐‐‐ C5a receptor

Correct answer C
The extended conformation of integrins corresponding to the high‐affinity state is activated in monocytes by recognition of MCP‐1 (on endothelial cells) by MCP‐1 receptor expressed on monocytes.

66

Deficiencies affecting the attachment of immune cells to blood vessel walls, cell movement, and interaction with complement fragments impair the ability of granulocytes and lymphocytes to migrate out of the intravascular compartment, to engage in cytotoxic reactions, and to phagocytose bacteria. Deficiency in which of the following molecular interactions will affect firm adhesion and diapedesis of neutrophils to inflammatory tissue?
A. E selectin ‐‐‐ sialylated carbohydrates
B. IL‐8 ‐‐‐ IL‐8R
C. MCP‐1 ‐‐‐ MCP‐1 receptor
D. beta2 integrin ‐‐‐ ICAM‐1
E. C5a ‐‐‐ C5a receptor

Correct answer D
The beta2 integrin (CD 18/CD 11) mediates firm adherence of adhesion neutrophils to vascular endothelium and allows transendothelial migration of leukocytes into sites of inflammation. The lack of beta2 integrin results leukocyte adhesion deficiency (LAD). Most patients with LAD have a poor outcome, with few infants surviving past 1 year of age. Bacterial infections and severe viral infections are responsible for most deaths. Delayed umbilical cord separation is the classic presentation of LAD.

67

Chronic granulomatous disease (CGD) is a rare (1:250,000 births) disease caused by mutations in any one of the five components of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase that leads to recurrent or persistent bacterial and fungal infections and to granuloma formation. CGD primarily affects
A. Recruitment of neutrophils
B. T cell activation
C. The ability to kill pathogens via the respiratory burst
D. Susceptibility to viruses
E. Antibody production

Correct answer C
NADPH oxidase in phagocytes generates superoxide and is essential for intracellular killing of pathogens by phagocytes.

68

Which of the following would be most worrisome for the presence of a primary immunodeficiency disease consisting of a problem with T lymphocyte function?
A. Recurrent ear, sinus and lung infections
B. Recurrent thrush (an infection of the mouth caused by yeast) or no thymus on chest x‐ray
C. Recurrent skin abscesses or poor wound healing
D. Recurrent warts

Correct answer B
T lymphocytes are critical for protection, especially against a number of fungal and viral pathogens. These immune cells develop within the thymus gland, and absence of a thymus on a chest x‐ray in a young infant can be a sign of missing T lymphocytes. Congenital absence of T lymphocytes is a medical emergency and must be treated immediately.

69

A major future of feature of acute bacterial infections is leukocytosis. Neutrophils usually predominant at the site of inflammation. Which of the following chemoattractants is a product of microbial metabolism?
A. C3 component of complement
B. C5a fragment
C. Histamine
D. N‐formyl methionine
E. Leukotriene B4

Correct answer D
N‐formyl methionine and LPS are two bacterial products that are chemoattractants for phagocytes (neutrophils and macrophages). C5a is also very potent chemoattractant but is produced by C5 convertase in humans.