Adaptive Immunity-D4

Question 1

Affinity maturation

Answer 1

B cells produce antibodies with increased affinity for an antigen during an immune response. This is linked to class switch recombination

Question 2

Class switch recombination (CSR)

Answer 2

Also referred to as isotype switching. B cells shift from making IgM antibodies to another isotype (IgA, IgE or IgG). This process is T cell dependent and requires stimulation of CD40 on B cells, followed by their expression of activation-induced cytidine deaminase (AID)

Question 3

Clonal expansion

Answer 3

The production of daughter cells arising from a single cell. The activation of a B cell or T cell by antigen will result in its clonal expansion, generating thousands of lymphocytes that have the same antigen specificity. Clonal expansion occurs simultaneously with effector differentiation

Question 4

Contraction

Answer 4

Deletion of antigen-specific effector T cells following their clonal expansion phase. Compared to the peak of clonal expansion, over 90 percent of the effector T cell pool will undergo apoptosis

Question 5

Differentiation

Answer 5

The stable acquisition of specific functions by a cell type. Differentiation occurs during development, in which the progeny from stem cells or precursor cells have a more limited, or specialized, developmental potential than their parent cell. During immune responses, differentiation results in naïve T cells acquiring effector functions, e.g. the ability to produce IFN- (Th1) or secrete cytotoxic granules (CD8+). B cell differentiation occurs in lymph node germinal centers and includes isotype switching, somatic hypermutation and affinity maturation

Question 6

Effector T cell

Answer 6

T cell that is actively responding to antigens. Following their activation by antigen presenting cells, naïve T cells differentiate into effector T cells, which can direct immune responses by secreting cytokines (CD4+), or secrete cytotoxic granules on their target cells (CD8+).

Question 7

Fc Receptor (FcR)

Answer 7

Receptor expressed by myeloid-derived cells that binds to the constant region of antibodies. One of the functions for Fc receptors is to aid the phagocytosis of antibody-coated bacteria or viruses by macrophages. Fc receptors are also required for antibody-dependent cellular cytotoxicity mediated by NK cells

Question 8

Memory lymphocyte

Answer 8

B or T cells that are derived from effector cells and provide a long-lived reservoir of antigen-specific cells following the contraction phase of a response. Memory cells can survive for years and mount a rapid recall response following secondary exposure to their antigen

Question 9

Naïve lymphocyte

Answer 9

Mature B or T cell that has not yet encountered antigen

Question 10

Plasma cell

Answer 10

Terminally differentiated B cell that has undergone isotype switching and somatic mutation. Plasma cells are specialized for secreting high levels of antibodies

Question 11

Somatic hypermutation

Answer 11

The mechanism responsible for affinity maturation of an antibody response. This process is T cell dependent and linked to isotype switching. Stimulation of CD40 on B cells results in their expression of activation-induced cytidine deaminase (AID). This enzyme generations random mutations in DNA encoding the antibody variable region. Some mutations will cause the antibody to have increased affinity for antigen, while some mutations will result in decreased affinity. B cell clones that make high affinity antibodies are preferentially selected to survive