EARLY TUMOR EFFECT ON SPLENIC TH LYMPHOCYTES IN MICE

Tumors are characterized by their ability to avoid the host immune sys tem, Ehrlich ascites tumor cells were used to investigate the early al terations of the host immune system after tumor inoculation, The resul ts show that frequencies of splenic Th lymphocytes were drastically re duced during tumor growth, reaching a minimum only two days after tumo r inoculation, The frequency of splenic CD4(+) lymphocytes expressing IFN-gamma was significantly increased, although the total number was u nchanged, suggesting that there was no net induction of Th1-type respo nse. Splenic macrophages were increased, in both frequency and cell nu mber, after four days of tumor growth, The same pattern was observed w hen mice were inoculated with cell free ascitic fluid, TGF-beta precur sors mere detected in tumor cells as well as in ascitic fluid, The dat a suggest that tumor actively interacts with host immune system by mea ns of tumor cell secreted factors. (C) 1997 Federation of European Bio chemical Societies.