In comparing spleen cells of inbred and congenic mice for spontaneous capacity to lyse cells of the BALB/c leukemia RLc♂1 in vitro, we found that the activity of 129 spleen cells was more than double that of 129-Gix- spleen cells. The only known difference between these two strains is that 129-Gix- mice express no known demonstrable gp70 or p30, whereas 129 mice express both these MuLV-related components as mendelian traits not associated with the production of virions. We infer that MuLV-related components at the cell surface are concerned in effector-target interactions leading to cytolysis under the conditions described. - Although the congenic strains B6 (Gix-) and B6-Gix+ differ likewise in expression of the type-variant Gix-gp70, both strains express a second type-variant of gp70. The lytic activity of spleen cells of these two strains for RL♂1 cells was equally high, suggesting that involvement in lytic effector-target interactions is common to gp70 molecules in general. - When used as targets rather than as effectors 129 spleen cells were more sensitive to lysis than 129-Gix- spleen cells. Pre-exposure to gp70, purified from R-MuLV, rendered splenic effector cells less lytic. Pre-exposure to gp70 also rendered RL♂1 target cells less sensitive to lysis. One explanation of these findings is that both target cells and effector cells express gp70 and also receptors for gp70 and that this is the basis of mutual cellular recognition leading to lysis in the circumstances described.
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