Administration of peripheral-blood rat-lymphocytes stimulated "in vitro" with human lymphokines and spleen colonies in the total body irradiated rat.

It was previously reported that PHA-incubation of a pool of peripheral-blood lymphocytes before their i.v. injection into rats submitted to total body irradiation, stimulates spleen colony formation and growth. On the same model, the present study has investigated the effect of lymphocyte preincubation with supernates obtained in short term cultures from human lymphocytes prestimulated with PHA (lymphokines). The "in vitro" culture of rat lymphocytes in a medium supplemented with human lymphokines showed either a marked increase of lymphocyte survival rate, or significant stimulation of lymphocyte blastogenesis, but at an extent much lower than that caused by PHA, also because in this particular experiment the culture medium was supplemented with too little amount of lymphokines. These data support the interpretation that human lymphokines may act across the species barriers. Peripheral-blood rat lymphocytes prestimulated with human lymphokines, and then injected i.v. into rats previously submitted to total body irradiation, caused significant increase in the spleen weight, as well as formation of spleen colonies quite larger and with higher erythroid differentiation - though less numerous than in the controls (i.e., in the rats injected just with untreated lymphocytes). This behaviour may be due to the tendency to merge together of two or more colonies in a single giant colony, and supports the interpretation that immune-competent lymphocytes activated either with PHA or with lymphokines may stimulate spleen colony growth and erythroid differentiation, though at different extents.