A B-cell subpopulation relatively insusceptible to the cytotoxic effect of anti-bursa cell serum and partially defective in immune function.

Chicken B cells treated with diluted anti-bursa cell serum in the presence of complement were transferred together with normal T cells and sheep red blood cells into immunodeficient recipient chickens, and spleen cells taken from these were examined for the development of plaque-forming cells. The production of IgM-plaque-forming cells was considerably more resistant to the cytotoxic effect of the antiserum than that of IgG-plaque-forming cells. Cells producing IgM antibodies were also less susceptible to the cytotoxic effect of the antiserum and complement than were those producing IgG antibodies. Such differential susceptibility of development of IgM- and IgG- plaque-forming cells was observed only in chickens aged about 2 weeks or younger. These findings indicate the existence of a B-cell subpopulation which is relatively insusceptible to the cytotoxic effect of the antiserum and is incapable of switching from IgM- to IgG-immune responses. The B cells resistant to the cytotoxic effect of diluted anti-bursa cell serum and complement were more susceptible to X-irradiation than were normal B cells. Immune responses against sheep red blood cells by the B cells resistant to the cytotoxic effect were dependent upon the help of T cells.