L3T4(-HELPER CELLS ARE REQUIRED FOR IN-VITRO MATURATION OF IN-VIVO PRIMED T-CELLS IN THE CYTOTOXIC RESPONSE TO MHC CLASS-I DISPARATE CELLS FOLLOWING FOOTPAD IMMUNIZATION() BUT NOT LYT2(+) T)

The induction characteristics of major histocompatibility complex (MHC ) class I-specific cytotoxic T lymphocytes (CTL) after footpad immuniz ation were studied. Primary CTL were generated in the regional lymph n odes of C57Bl/6 mice by footpad injection with 10(7) irradiated (2000 rad) spleen cells from MHC class I mutant mouse strain (bm1) followed by a short in vitro culturing without antigen. The requirement of acce ssory cells and L3T4(+) T cells during in vitro maturation of in vivo primed CTL precursor (CTL(p)) was shown. Moreover, using inhibitory an tibodies, the need for IL-2 and IL-4 for in vitro maturation of CTL wa s established. We have suggested that accessory cells act at the level of L3T4(+) T cells which in turn non-specifically up-regulate the CTL response through the production of growth and differentiation factors . Thus, the T-helper population of L3T4(+) but not Lyt2(+) phenotype a ppears to be recruited in the in vitro maturation of in vivo primed CT L(p) in a given system. Possible mechanisms of this phenomenon are dis cussed.