ABSTRACT
The immunologic status of the guinea pigs was modified by treatment with antithymocyte serum (ATS): irradiation of gastrointestinal tract lymphoid tissue (GALT) and bone marrow (BM) by gamma-rays. These animals were injected with homologous testes, kidney and heterologous sheep red blood cells respectively in complete Freund's adjuvant. Cell mediate immune response (CMI) and humoral immune response was studied after first, third, fifth and eighth week of allergization. CMI was completely suppressed in guinea pigs treated with ATS, whereas humoral response suppressed to a lesser extent. In GALT and BM irradiated guinea pigs, CMI develops normally. However, marked suppression in the production of antibody titre both against homologous testes, kidney and heterologous sheep red blood cells was observed. Thymic lymphocytes "T' are destroyed by antithymocyte serum which are the mediators of cell mediated immune response. Irradiation of GALT and BM suppresses humoral response thereby supports that these are populated by "B' lymphocytes.