T15-specific helper T cells: analysis of idiotype specificity by competitive inhibition analysis.

Optimal activation of T15 idiotype-bearing B cells has been shown previously to be influenced by two subsets of Thy-1+, Ly-1+,2-sIg- helper T cells. One of the helper T cell sets appears to be T15 specific in that its presence results in a selective augmentation of T15-bearing anti-phosphorylcholine (PC) plaque-forming cell responses. To determine the precise specificity of the idiotype-specific helper T cell (ThId), Ly-1 T cells were tested in an in vitro anti-PC response for their ability to bind directly to T15 myeloma protein-coated plastic plates. Specificity of this binding was ascertained by competitive inhibition of plate binding using idiotypically related myeloma or hybridoma proteins. These data suggest that the Ly-1 T cells which augment T15-bearing plaque-forming cell responses can bind to T15-coated plates and are T15 idiotype specific. This approach is being used currently to attempt to clone ThId cells to further analyze their activation requirements and specificities.