Further studies of thymus-bone marrow cell synergism in cutaneous manifestations of delayed hypersensitivity to methylated human serum albumin. The effect of cortisone acetate.

The contribution of syngeneic bone marrow and thymus cell populations obtained from normal and cortisone-treated donor mice for reconstitution of delayed hypersensitivity to methylated human serum albumin (MHSA) was studied in lethally irradiated recipients employing a limiting dilution assay. Normal thymus cells contained at least one antigen-reactive cell (or cell unit) per 3.7 × 10 cells, while cortisone-resistant cell populations contained one cell per 6.7 × 10 cells. Thus, cells immunocompetent to MHSA are not destroyed by steroid. Bone marrow cell populations contribute effector cells, and as few as 2 × 10 cells are capable of fully restoring delayed response when combined with optimum numbers of thymus cells. Large numbers of thymus cells alone will restore immune responsiveness, indicating that such populations do contain some effector cells, either as contaminating blood borne cells, or as glandular cells derived possibly from sinusoids. Similarly, bone marrow cells in larger numbers restore responsiveness, implying contamination with thymus-derived cells.