Updated: 6/17/2021

Immunology

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  • Types of Immune Responses
    • 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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(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:

QID: 4675
1

The patient is at a significantly higher risk of surgical infection

33%

(1246/3778)

2

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

46%

(1738/3778)

3

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

12%

(453/3778)

4

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

2%

(70/3778)

5

The patient is more likely to be female than male

7%

(246/3778)

L 5 C

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

QID: 2945
1

Packed red blood cell transfusion

13%

(188/1453)

2

Platelet transfusion

3%

(40/1453)

3

Immune inert scaffold placement

6%

(93/1453)

4

Metal plate and screw placement for fracture

68%

(992/1453)

5

Red man syndrome from vancomycin administration

9%

(134/1453)

L 3 D

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(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?

QID: 490
1

Antigen phagocytosis by T cells

5%

(95/1768)

2

Antigen processing and presentation to T cells

82%

(1456/1768)

3

Antigen recognition by natural killer T cells

10%

(180/1768)

4

Antigen proliferation by polymerase chain reaction

1%

(18/1768)

5

T cell disulfide bond cleavage and enzymatic processing

1%

(11/1768)

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?

QID: 889
1

IgA

5%

(33/697)

2

IgD

0%

(0/697)

3

IgE

7%

(48/697)

4

IgG

13%

(90/697)

5

IgM

75%

(525/697)

L 3 D

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