Helper and Suppressor Functions of Thymus-Derived Lymphocytes in the Humoral Response to Heterologous Erythrocytes in Rabbits.

Two functionsf helper and suppressor activity, of the thymus-derived lymphocyte (T-cell) in the humoral antibody response of rabbits to sheep erythrocytes (SRBC) were investigated. In the first aspect of this study splenic plaque-forming cell (PFC) and humoral' hemolysin responses to SRBC were examined in adult thymectomized, lethally x-irradiated rabbits infused with allogeneic bone marrow (BM) and thymus cells from cortisonetreated littermate donors. Seven to eight week old rabbits were thymectomized and at eight to ten weeks of age received 900R total body x-irradiation. One portion of this group was infused intravenously (iv) with the total BM (B-cell source) and thymus cell populations from cortisone-treated Q littermate donors. Another group received *20 x 10 nucle­ ated BM cells. The remaining animals received no reconsti­ tuting cell populations. All groups were immunized iv with 1.0 ml of a 10 percent suspension of SRBC. Peripheral white blood cell counts (WBC) and anti-SRBC hemolysin titers were determined on selected days after immunization. Represent­ ative animals from each group were killed on the seventh day after immunization and,their spleens were assayed for anti-SRBC PFC activity. Hemolysin responses in the BM re­ constituted and non-reconstituted animals were minimal when compared to the control group responses. Those animals xiii xiv which received both EM and thymus cells showed a delayed but significant rise in hemolysin responsiveness which approached that of the normal control group. The PFC data reflected the hemolysin responses as the non-reconstituted and BM reconstituted animals showed responses less than background. The infusion of BM and thymus cellssignificantly restored the number of PFC (*1-8,3 per million cells) when compared to the normal control response (50.8 per million cells). These data support the need for syn­ ergism between the Tand B-cell population in the humoral response to SRBC in rabbits. In the second aspect of this study horse anti­ rabbit thymus gamma globulin (ATGG) was used to investi­ gate the suppressor function of the T-cell in antigenic competition between heterologous erythrocytes. Eight week old rabbits were injected iv with 1.0 ml of a 20# horse red blood cell suspension (2xHRBC) followed three days later with IxSRBC. ATGG was injected two days before, on the. same day and two days after HRBC injection (Test group). The effect of ATGG was controlled by substituting normal horse gamma globulin (NHGG) or ATGG which had been adsorbed with thymocytes (ATGG-adsorbed control). An additional control group was injected with HRBC and SRBC only (compe­ tition) . Anti-SRBC PFC responses were assayed on the 5th day podt SRBC injection. The competition group showed a supressed response (29 PFC/10̂ ) when compared to the normal non-competitive anti-SJRBC responses (72 PFC/10^). ATGG-treatment alleviated this antigen-induced suppression and these animals showed a marginally enhanced response (90 PFC/10^). The NHG6 and ATGG-adsorhed control groups were not significantly different from the competition group. The anti-SRBC hemolysin responses reflected the PFC data. These results suggest ATGG interfered with the suppressive effect of a priming injection of HRBC on the subsequent anti-SRBC response in rabbits. Chapter 1 REVIEW OF LITERATURE