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Medical Microbiology I > Antigen-Specific Immune Responses > Flashcards

Antigen-Specific Immune Responses Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Antigen specific immune responses

A
  • Expand the host protection provided by innate immune responses
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2
Q

Antigen specific immune responses are provided by

A
  • T cells

- Antibodies

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3
Q

Almost any molecule has the potential to

A
  • Initiate an immune response
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4
Q

Features of antigen specific immune responses

A
  • Randomly generated
  • Regulated response
  • Inducible response
  • Ignores “self” proteins
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5
Q

Central immune tolerance

A
  • During fetal growth the body develops “tolerance” towards self-antigens
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6
Q

Peripheral tolerance

A
  • Develops later in life

- Tolerance to other proteins to prevent uncontrolled or autoimmune responses

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7
Q

Class I MHC antigens

A
  • Expressed on the surface of all nucleated cells
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8
Q

Class II MHC antigens

A
  • Expressed by antigen-presenting cells (APCs)

- Dendritic cells , macrophages and B lymphocytes

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9
Q

Immunogen

A
  • A protein or carbohydrate that challenges the immune system
  • Induces an immune response
  • May contain more than one antigen
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10
Q

Antigens

A
  • A molecule that is recognized by a specific antibody or a by a T cell antigen receptor (TCR)
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11
Q

Epitope

A
  • Actual molecular structure that interacts with a single antibody molecule or TCR
  • Also called the “antigenic determinant”
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12
Q

Monoclonal antibody recognizes

A
  • A single epitope
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13
Q

Immunogen performance

A
  • Not all molecules are immunogens
  • Proteins = best
  • Carbohydrates = weaker
  • Lipids and nucleic acids = poor
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14
Q

The type of immune response initiated by an immunogen depends on the molecular structure

A
  • Rapid antibody response initiated towards bacterial polysaccharides, peptidoglycan, or flagellin
  • Due to repetitive structure of these molecules
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15
Q

T-independent antigens

A
  • Large repetitive structures

- Polysaccharides, peptidoglycan, LPS

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16
Q

T-independent antigens primitive response

A
  • Fails to stimulate an anamnestic response (production of an antibody due to previous stimulation by the same antigen)
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17
Q

T-dependent antigens (proteins)

A
  • Must be presented to T and B cells for antibody production
  • Able to stimulate all 5 classes of immunoglobulins
  • Elicit an anamnestic response
18
Q

T-cell help needed to stimulate

A
  • Response with memory
19
Q

Adaptive immune response initiated when

A
  • Receptors of lymphocytes recognize antigens
20
Q

B cells antigen receptors

A
  • Antibodies that can recognize a wide variety of molecules (proteins, polysaccharides, lipids, nucleic acids)
21
Q

T cells

A
  • “See” only peptide fragments of protein antigens

- Can only “see” when peptides are presented by specialized peptide display molecules on host cells

22
Q

Antigens recognized by T cells

A
  • Recognize peptide antigens that are bound to and displayed by major histocompatibility complex (MHC) molecules of antigen-presenting cells (APCs)
23
Q

Major histocompatibility complex (MHC)

A
  • A genetic locus whose principal products function as the peptide display molecules of the immune system
24
Q

MHC restriction

A
  • In every individual, different clones of T cells can see peptides only when these peptides are displayed by that individual’s MHC molecules
25
Q

How do the rare lymphocytes specific for any microbial antigen find that microbe?

How does the immune system produce the effector cells and molecules best able to eradicate a particular infection?

A
  • The immune system has developed a highly specialized system for capturing and displaying antigens to lymphocytes
26
Q

Distinguishing surface markers of T cells

A
  • TCR – T cell receptor
  • CD2
  • CD3
  • CD4 or CD8
27
Q

Antigens recognized by T cells

A
  • T cell receptor (TCR) recognizes some residues of a peptide antigen
  • TCR recognizes residues of the MHC molecule that is displaying that peptide
28
Q

How T cell receptor recognizes peptide antigen

A
  • Dual specificity
  • MHC on antigen-presenting cells display peptides derived from protein antigens
  • Peptides bind to the MHC molecules
  • TCR of every T cell recognizes some residues of the peptide and some residues of the MHC molecule
29
Q

Antigen-presenting cells

A
  • Specialized cells that capture microbial antigens and display them for recognition by T lymphocytes
30
Q

Naive T lymphocytes need to see protein antigens presented by

A
  • Dendritic cells: the most effective “professional” APCs to initiate clonal expansion and effector cell differentiation
31
Q

Differentiated effector T cells again need to see antigens, presented by various APCs, to activate

A
  • Effector functions of the T cells in humoral and cell-mediated immune responses
32
Q

T cell development

A
  • Thymus: genetic events generate numerous TCRs
  • Each TCR expressed on a different T cell clone
  • Those that cannot interact with MHC do not grow
  • Those that react with host are signaled for apoptosis
33
Q

T cells are distinguished by

A
  • Type of T-cell antigen receptor they express
  • Either consisting of γ and δ chains or α and β chains
  • Further distinguished by the cytokines they produce
34
Q

Distinguishing factor of α/β T cells

A
  • Presence of CD4 or CD8 co-receptors
35
Q

Specificity of the TCR determines

A
  • Antigenic response of the T cell
36
Q

Each TCR molecule

A
  • Each made up of two different polypeptide chains (α and β)

- Each chain has a constant region and a variable region (like antibody)

37
Q

TCR chains are anchored in

A
  • Plasma membrane
38
Q

TCRs are not produced in

A
  • Secreted form
39
Q

TCR repertoire

A
  • Very large
  • Identify a large number of antigenic specificities
  • Estimated to recognize 10^15 separate epitopes
  • TCRs bind antigen presented with the MHC molecules
40
Q

Structure of T cell receptor gene

A
  • Genetic mechanisms for the development of the diversity is similar to those for antibody
41
Q

TCR gene composition

A
  • Multiple V (V1V2V3 … Vn), D, and J segments
  • Only cells with functional TCRs will survive
  • Each T-cell clone expresses a unique TCR

Medical Microbiology I (8 decks)

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