B CELL ACTIVATION
a. Early evidence about hapten-carrier systems suggests that T cells recognize
the carrier while B cells recognize the hapten. As discussed previously, haptens alone
are not able to induce immune responses. If the hapten is coupled to a carrier, antibody
that reacts with the hapten will be produced. The B cell which binds the hapten will
make antihapten antibody.
b. It was recognized that helper T cells were actively involved in helping rather
than passively focusing antigen. Another mechanism proposed that helper T cells exert
their effect through the release of diffusible factors called lymphokines which act on
local B cells. These factors may be immunologically specific or nonspecific.
ANTIBODY AND MEMORY B CELL PRODUCTION
Once B cells are stimulated, they become metabolically active and undergo
morphological changes (Figure 3-2). This process is called blast transformation.
B lymphocytes are small oval cells, but after transformation they become enlarged.
B cells then go through several cell divisions called clonal expansion in order to
increase the number of activated cells. They then differentiate into plasma cells and
memory B cells. Plasma cells secrete antibodies. They are end cells and survive only
about two weeks. Memory cells have the same appearance as small lymphocytes.
Exactly how they arise is not known. Memory cells are responsible for the anamnestic
response, the rapid production of antibody on re-exposure to antigen.
Figure 3-2. B cell proliferation to form antibodies.