Q.Explain the mechanism of humoral immunity.

Humoral immunity is the antibody-mediated arm of the specific immune response, most effective against pathogens and toxins that are free in the body's fluids ("humors") — blood, lymph and tissue fluid — rather than hidden inside a host cell.

The response begins when an antigen is taken up and processed by an antigen-presenting cell (APC), which displays fragments of it on its surface. A helper T-cell (TH cell) that recognises this displayed antigen becomes activated, and in turn helps activate a B-cell that has independently bound the same antigen through its own surface receptor. This activated B-cell then proliferates and differentiates into two cell types: plasma cells, which secrete large quantities of antibody specific to that antigen, and memory B-cells, which persist long after the infection is cleared and allow a much faster, stronger response if the same antigen is ever encountered again. …