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The antibody response to rabbit gamma-globulin (RGG) of high-responder, but not of low-responder Biozzi mice decreased with age. Injection with aggregate-freed RGG reduced the response of high-responder but not of low-responder mice to subsequent injections with aggregated RGG. This reduction in the antibody response, formed by high-responder mice, decreased with increasing age; aggregate-freed RGG appeared to sensitize 6-month-old low-responder mice to a subsequent injection with aggregated RGG. When animals, not pretreated with aggregate-freed RGG, were immunized with RGG and lipopolysaccharide (LPS), the immune response was greatly enhanced. The response of both pretreated low and high responders was substantially smaller than that of corresponding animals which were not given aggregate-freed RGG, prior to immunization. LPS revealed an inhibitory effect on low-responder mice of aggregate-freed RGG, which was not detected upon immunization with heat-aggregated RGG alone. The involvement of nonspecific suppressor cells and of B cell tolerance in low-responder mice is discussed.

The migration of 51Cr-labeled autologous lymphocytes from intestinal or prescapular lymph was compared in fetal lambs and adult sheep. A subpopulation of lymphocytes present in intestinal lymph of adults which migrated to the small intestine was not found in fetal intestinal lymph. There were marked differences in the migration of fetal and adult lymphocytes to the lungs and liver. In spite of the absence of circulating antibodies or immunoglobulins and of extrinsic antigen in the immunologically virgin sheep fetus, the circulation of lymphocytes through the spleen and lymph nodes of fetal lambs was more intense than in the adult.