Updated: 10/10/2016

Immunology

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Introduction
  • Types of Immune Responses
    • innate response 
      • not specific to a type of immunological challenge
      • represents the immune response which does not have memory
        • e.g.,  anatomic barriers (skin), inflammation, complement cascade
      • recognizes structures common to multiple microbes
      • found in nearly all forms of life
      • cells include
        • natural killer cells
        • mast cells
        • eosinophils
        • basophils 
        • phagocytic cells (macrophages, neutrophils, and dendritic cells)
    • acquired response
      • portion of immune response which has memory
      • occurs in a pathogen and antigen specific mechanism
      • requires antigen processing and presentation  
        • performed by antigen presentation cells (APC) 
          • B cells and dendritic cells are two examples of APCs
        • the APC breaks down the protein antigen in a multitude of enzymatic reactions and presents key peptide sequences via the major histocompatibility complex (MHC) receptors 
        • once presented on the surface of the APC, the T-cell receptor recognizes the MHC/antigen complex prior to T-cell activation
      • cells include
        • CD8+ T lymphocytes
        • T helper cells
        • delta gamma T cells
        • B cells and plasma cells
Types of Immunological Reactions
  • Type I: Immediate anaphylactic reaction
    • associated with allergy  
    • mediated by IgE antibody activation of mast cells and basophils
  • Type II: Antibody dependent (aka cytotoxic) hypersensitivity
    • mediated by IgG and IgM antibodies
  • Type III: Immune complex (antigen bound to antibody) deposition type of hypersensitivity
    • mediated by IgG and IgM antibodies which when bound to antigen get deposited in various tissues
  • Type IV: Delayed-type or cell-mediated hypersensitivity
    • mediated by T cells, monocytes and macrophages
    • take several days to develop
    • examples include
      • tuberculosis skin test
      • the immune response to metallic orthopaedic implants is typically a Type IV (delayed-type hypersensitivity reaction) 
Immunoglobulins
  • Immunoglobulin types
    • IgG
      • the most abundant immunoglobulin
    • IgM
      • the first class of antibody to appear in our serum after exposure to an antigen 
    • IgA 
      • the major class of antibody in external secretions (e.g. intestinal mucus, bronchial mucus, saliva, and tears)
    • IgE
      • important in conferring protection against parasites and allergic reactions

Immunologic Variations

  • Benign Ethnic Neutropenia 
    • Most common neutropenia in the world
    • Approximately 25%-50% of people of African descent and some sub-groups in the Middle East found to have low ANC without increased infection risk 
    • ANC < 1.5 x 10(9) cells/L considered "abnormally low" without clear clinical relevance.
      • 4.5% African Americans, 0.79% white Americans, 0.38% Mexican-Americans below this ANC
    • Also more common in males vs females, athlete vs non-athlete, and children under age 5
 

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Questions (5)
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(OBQ13.40) A healthy patient undergoes routine pre-operative laboratory testing and is found to have a leukocyte count of 1.5 × 10(9) cells/L. When the historical records are examined, this is found to be the patients base-line level over a period of years. Which of the following statements is most likely to be true: Review Topic | Tested Concept

QID: 4675
1

The patient is at a significantly higher risk of surgical infection

33%

(1184/3567)

2

The patient is more likely to be of African than of European descent

46%

(1634/3567)

3

The patient is more likely to be of European than of Middle Eastern descent

12%

(429/3567)

4

The patient is more likely to be a non-athlete than an athlete

2%

(63/3567)

5

The patient is more likely to be female than male

7%

(233/3567)

L 5 C

Select Answer to see Preferred Response

(OBQ09.132) A type IV (delayed-type hypersensitivity reaction) can be seen in which of the following scenarios? Review Topic | Tested Concept

QID: 2945
1

Packed red blood cell transfusion

13%

(175/1362)

2

Platelet transfusion

3%

(41/1362)

3

Immune inert scaffold placement

6%

(86/1362)

4

Metal plate and screw placement for fracture

68%

(932/1362)

5

Red man syndrome from vancomycin administration

9%

(122/1362)

L 3 D

Select Answer to see Preferred Response

(OBQ08.104) The acquired immune response mediated by the interaction between the T cell receptor and major histocompatibility complex requires which of the following first steps? Review Topic | Tested Concept

QID: 490
1

Antigen phagocytosis by T cells

5%

(84/1652)

2

Antigen processing and presentation to T cells

83%

(1374/1652)

3

Antigen recognition by natural killer T cells

10%

(159/1652)

4

Antigen proliferation by polymerase chain reaction

1%

(16/1652)

5

T cell disulfide bond cleavage and enzymatic processing

1%

(11/1652)

L 2 D

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(OBQ07.228) What is the first class of antibody to appear in serum after exposure to a foreign antigen? Review Topic | Tested Concept

QID: 889
1

IgA

5%

(29/588)

2

IgD

0%

(0/588)

3

IgE

7%

(44/588)

4

IgG

12%

(73/588)

5

IgM

75%

(441/588)

L 3 D

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