Ly‐6 A/E antigen of murine T cells is associated with a distinct pathway of activation. Requirements for interferon and exogenous interleukin 2

The Ly‐6 pathway of T cell activation was analyzed to identify its essential requirements. Using a monospecific chicken antiserum to Ly‐6E, fully cross‐reactive to its allelic counterpart, Ly‐6A, but unreactive with other members of the Ly‐6 family, we have found that interferon (IFN)‐α/β or γ, Ly‐6 antibody and interleukin 2 (IL2) act synergistically in inducing T cell proliferation. The action of IFN can be attributed to induction of Ly‐6 A/E antigen on T cells, as described previously, and this induction is transcriptionally controlled. Exposure of T cells with elevated Ly‐6 concentrations to chicken anti‐Ly‐6 antibody leads to expression of IL2 receptors. Consequently, the addition of IL2 drives T cell proliferation. Thus, in BALB/c mice the minimum requirements for activation by the Ly‐6 pathway are IFN (as a means of inducing Ly‐6), Ly‐6 antibody (as inducer of IL2 receptors) and IL2. In mice of the Ly‐6. 2 haplotype, IFN is not an absolute requirement. This may be related to the fact that these animals, in contrast to those of Ly‐6.1 haplotype, express Ly‐6 constitutively on a substantial proportion of resting T cells. Thus, T cells of C57BL/6 or DBA/2 mice can be induced to proliferate with Ly‐6 antibody and IL2 alone, although IFN pre‐treatment enhances this response. In BALBic mice the IL2‐driven proliferative response induced through the Ly‐6 pathway occurs selectively in the L3T4− population.