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Involvement of NK1+ CD4- CD8- alphabeta T cells and endogenous IL-4 in non-MHC-restricted rejection of embryonal carcinoma in genetically resistant mice.

Non-MHC-restricted rejection mechanisms against the murine MHC-negative F9 embryonal carcinoma cells were analyzed. Strains of C57BL/6 (B6) background were resistant to the tumors irrespective of H-2 haplotypes, while others, including BALB/c background, were susceptible. This resistance was suggested to be mediated primarily by the host thymus-dependent alphabeta T cells, since both athymic B6 nude and normal B6 mice depleted with alphabeta T cells showed susceptible phenotype. The difference of the nature of alphabeta T cells infiltrating in H-2-identical B6- and BALB.B-derived tumors was then comparatively analyzed. It was revealed that unique T cells with NK1+ CD4- CD8- (double negative (DN)) alphabeta TCR+ phenotype were accumulated significantly in B6, but few in BALB.B mice. The population freshly isolated from the F9 tumor tissues preferentially expressed potent IL-4 mRNA, and was suggested to be mostly responsible for the endogenous IL-4 production. Indeed, the injection of either anti-NK1.1 or anti-IL-4-neutralizing Ab into the normal B6 rendered them significantly susceptible to the tumor cells. These results strongly suggested that NK1+ DN alphabeta T cells were responsible primarily for the rejection mechanisms against F9 tumors. Histologically, F9 tumors in B6 mice were characterized by abundant macrophage infiltration and massive tumor necrosis, neither of which was observed in those in BALB.B nor B6 mice preinjected with anti-IL-4 Ab, indicating that both histologic features in the resistant strain were dependent on the endogenous IL-4. Present results provide one of the first instances in which a recently emerging minor T cell subpopulation, thymus-dependent NK1+ DN alphabeta T cells, plays an essential role in anti-tumor responses in vivo.