AP BIOLOGY

Detailed explanation-1: -Ig heavy chain class switching occurs rapidly after activation of mature naïve B cells, resulting in a switch from expressing IgM and IgD to expression of IgG, IgE, or IgA; this switch improves the ability of antibodies to remove the pathogen that induces the humoral immune response.

Detailed explanation-2: -Immunoglobulin heavy-chain gene rearrangement begins in early pro-B cells with D to JH joining. This typically occurs at both alleles of the heavy-chain locus, at which point the cell becomes a late pro-B cell. The cell then proceeds to rearrange a VH gene segment to the DJH sequence.

Detailed explanation-3: -Plasma cells derive from three distinct pathways. Naïve B cells can be directly activated by antigen and undergo class switch recombination (CSR) without T cell help, forming unmutated PCs. Alternately, T helper (TH) cells can activate B cells through cognate contact, and direct CSR via secreted factors.

Detailed explanation-4: -IgM is not only the first class of antibody to appear on the surface of a developing B cell. It is also the major class secreted into the blood in the early stages of a primary antibody response, on first exposure to an antigen.

Detailed explanation-5: -Class switching is the process whereby an activated B cell changes its antibody production from IgM to either IgA, IgG, or IgE depending on the functional requirements.