35)Explain what are the molecular and functional changes that occur in memory B

Question

35)Explain what are the molecular and functional changes that occur in memory B cells in comparison to naive B cells? 36)What are the features that allow memory B cells to respond differently to activation in comparison to naive B cells? And how different is this response? 37)Explain the molecular and functional differences between naive T cells, effector T cells, effector memory Tcells and central memory T cells. 38) How do the differences in memory T cells in comparison to naive T cells allow them for a more efficient response upon re-challenge?

Explanation / Answer

35) B cell synthesis and maturation occurs in bone marrow. Before birth, the yolk sac, fetal liver and fetal bon marrow are sites of B cell maturation, After birth, generation of mature B cells occurs in the bone marrow.

Naive B cells or mature B cells on their surface has two membrane bound immunoglobulins - IgM and IgD with a single antigen specificty. The membrane bound antibody acts as an antigen receptor on the B cell surface. Ig-alpha and Ig-beta are also present on the membrane with Ig molecules, from pre-B cell to memory B cell, serves as B-cell receptor (BCR). Ig-alpha and Ig-beta (CD79a/CD79b) do not bind antigen but transmit signals to th nucleus, leading to a change in the pattern of genes expressed.

Naive B cells on first exposure to antigen, differentiates into Plasm B cells and memory b cells. Plasma B cells secretes IgM antibodies that helps in antigen neutralization, plasma B cells have short life span. But memory B cells lives in bone marrow, gut a long lived plasma B cells. During this time, Memory B cells undergo somatic hypermutation , followed by antigen selection. This results in the B cells with high affinity recptors for antigen. On second exposure to the same antigen, memory B cells responds immediately with the secretion of different antibodies, resulting in faster elimination of antigens. Memory B cells responds to lower concentrations of antigens than primary naive B-cells. Memory B cells carries mutated and selected B-cell receptors.

36) Naive B cells interacts with antigens for the first time, generates primary response, which usually takes 5-10days. B cells differentiates into Plasma- B cells and Memory B cells. Plasma B cells seretes IgM antibodies for antigen nuetralization and dies after primary response but memory B cells have longer life span and undergoes affinity maturation. On second exposure of the same antigen, memory B cells generates secondary response which usually takes 1-3days and secretes large amount of IgG antibody.

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