Helper T cell recognition of the variable domains of a mouse myeloma protein (315). Effect of the major histocompatibility complex and domain conformation.

We have examined the recognition of the variable (V) domain of the heavy (VH) and light (V lambda 2) chains of mouse myeloma protein 315 by helper T cells. Mice were primed with the isolated V domain in complete Freund's adjuvant, and carrier (V domain)-primed spleen cells were transferred together with hapten (NIP)-primed spleen cells to recipient mice that were boosted with NIP3-Fab-315. The helper cell response to both domains was governed by H-2-linked immune response (Ir) genes, and VH-315 and V lambda 2 displayed different Ir phenotypes. H-2k conferred high responsiveness to VH on three different genetic backgrounds, BALB/c, C3H, and B10; mice of the d and b haplotypes were low responders. Conversely, H-2d conferred high responsiveness to V lambda 2 on two backgrounds, BALB/c and C3H, whereas mice of the k haplotype were low responders to this domain. Non-H-2 genes of the B10 background extinguished the helper cell response to V lambda 2 in animals with the high responder d haplotype. The VH Ir gene mapped to the K-A interval of the H-2 complex. Unfolded (completely reduced and alkylated) V domains primed helper cells as efficiently as folded domains for responses to NIP3-Fab-315, indicating that the helper cells recognized an antigenic determinant that was not conformation-dependent. The data indicate that there exists helper T cells which recognize each member of the M315 pair of V domains independent of the other, and that these V domains are recognized like conventional extrinsic protein antigens.