Histological and autoradiographical findings in the immunologically stimulated spleen.

In order to estimate the role of a possible immunological coeffect on the splenic cellular proliferation during wound healing after mechanical or thermal lesions of internal organs, light microscopical and autoradiographical investigations with tritiated thymidine were performed on spleens of non-germfree rats, immunized by a single injection of sheep erythrocytes. Two days after an initial dissociation of preexisting germinal centers in the spleen a steep rise of the percentages of labeled cells in newly formed germinal centers occurs with a maximum on the fifth day. In the marginal zone an increased cell proliferation (mostly large lymphoid blasts) starts at 12 hours. In the lymphatic mantle zone a marked increase of labeled basophilic blasts (immunoblasts) can be observed with a maximum on the second day. The values are higher in the perifollicular B cell region than in the periarteriolar T cell region. In the red pulp of the spleen the highest percentages of labeled cells occur five days after the antigen injection. These findings in the spleen after a strong antigenic stimulation are characteristic for an immunological reaction of anamnestic type. In comparison with investigations of the spleen after cryolesions in internal organs such studies may be particularly helpful in judging the proportion of an unknown immunological reaction in the spleen after such an operation, which by tissue necroses and cellular destruction may have caused denaturation of self components.