1. Adult (A x C57Bl/1)F1 hybrids regularly show runt disease when injected with adult spleen cells from A strain donors. This also occurs when A strain spleen cells are administered to adult C3H mice made tolerant of A strain tissue in the neonatal period.
2. Mice undergoing the graft versus host reaction fail to form antibodies to an intraperitoneal challenge of T2 bacteriophage. This phenomenon was observed well before any of the other overt signs of runting had occurred. Further, inhibition of antibody production to T2 phage by graft versus host reaction initiated at an interval following antigenic stimulation is demonstrated.
3. The basis for the immunologic incompetence of the host with respect to T2 phage is presumed to be the attack of immunologically competent donor cells on the lymphoid cells of the recipient.
4. The failure of the injected parent strain cells to respond to the antigen used may imply immunologic commitment of these cells.