Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
The B cells exist to produce neutralising antibodies, which can help destroy unwanted invaders including foreign cells. (This is normally mediated by macrophages, which will digest any cells found with antibody attached to them.)
B cells need to be activated by chemical messengers such as lymphokines (produced by helper T cells) before they will start to emit antibodies. The below image shows the process of B cell activation, here by the cytokines interleukin-4 and interleukin-6. A "resting", inactivated B cell produces very little antibody, but when stimulated by the cytokines, it develops into a "B-blast", multiplies, and then matures into a plasma cell. A plasma cell is basically an activated B cell, emitting lots of antibodies into the body.