Stimulation of IgG antibody formation by sublethal irradiation during persistently repeated immunization with Brucella abortas.

Whole-body irradiation with 600 rads 8 or 10 days after the beginning of persistently repeated Brucella abortus immunization in the rabbit produces little change in the response. By contrast, irradiation with the same dose 2, 4 or 6 days after the beginning of repeated immunization stimulates the IgG response. This effect is explained by a repopulation of antigen-sensitive cells from precursor cells to a higher level than that previous to irradiation. In order to explain IgG stimulation, three main possibilities are considered. a) a T cell-dependent mechanism, consequent on a higher radioresistance of T than of B cells, or on a faster and more extensive repopulation by T cells; b) another T cell-dependent mechanism due to a greater radiosensitivity of the suppressor or inhibitory T-cell subpopulation, with the result of a predominance in the T cell population that helps IgG formation; c) a mechanism depending on antigen presence during the repopulation of antigen-sensitive cells from the precursor cells, according to previously obtained data suggesting the necessity for the persistence of a certain level of antigen for IgG formation