Example of an antibody-mediated immune response.

1. The B cell receptors on a naive B cell bind to an antigen on
the surface of a bacterium. The bacterium’s complement coating
triggers the B cell to engulf it. Fragments of the bacterium bound to
MHC markers become displayed at the surface of the B cell.
2. A dendritic cell engulfs the same kind of bacterium that the B cell
encountered. Fragments of the bacterium bound to MHC markers
become displayed at the surface of the dendritic cell.
3. The antigen–MHC complexes on the dendritic cell are recognized
by TCRs on a naive helper T cell. The two cells interact, and then
the T cell begins to divide. Its descendants differentiate into effector
helper T cells and memory helper T cells.
4. TCRs on one of the effector helper T cells recognize and bind to
the antigen–MHC complexes on the B cell. Binding makes the T cell
secrete cytokines.
5. The cytokines induce the B cell to divide again and again. Its many
descendants differentiate into effector B cells and memory B cells.
6. The effector B cells begin making and secreting huge numbers of
antibodies, all of which recognize the same antigen as the original B
cell receptor. The new antibodies circulate throughout the body and
bind to the bacteria.