The persistent PHA-responsive population in the mouse thymus. I. Characterization of the population.

Using an in vitro culture technique, mouse thymus graft cells were co-cultured with peripheral blood lymphocytes in the presence of phytohaemagglutinin (PHA). The persistent PHA-responsive thymus graft population (Elliott, 1973) was shown to be able to respond to other T-cell mitogens (Con A, pokeweed mitogen, staphylococcal enterotoxin B), but not to E. coli lipopolysaccharide a known B-cell mitogen. The percentage of persistent PHA-responsive cells did not alter during 5 days in culture and was relatively unaffected by either hydrocortisone or anti-lymphocyte serum treatment in vivo. In allogeneic thymus grafts (AKR leads to CBA), persistent PHA-responsive cells could be demonstrated, which were destroyed when incubated with CBA anti thetaAKR serum and complement. When thymus graft cells were allowed to sediment on a 0.2--2 per cent BSA gradient, it was seen that the PHA-responsive population sedimented faster than the bulk of thymus graft cells. Some separation could be obtained on this gradient between the persistent and non-persistent PHA-responsive cell populations.