gamma gene rearrangements similar to those described for cytotoxic T cell lines are found in L3T4+, autoreactive, or KLH-specific cloned helper T cell lines. High levels of gamma RNA transcripts were, in addition, detected in four out of five L3T4+, class II MHC-specific, autoreactive T cell clones, and in at least one of three KLH-specific, class II MHC-restricted clones. This contrasts with previously reported (9) expression of gamma RNA in only 1 of 11 antigen-specific helper T cell lines.
We have attempted to determine whether T cells and B cells that have the same antigenic specificity and whose receptors share idiotypic determinants in fact express similar VH gene segments. To do this, we have obtained and characterized a cDNA clone containing the entire coding sequence for the VH gene from a glutamic acid60/alanine30/tyrosine10 (GAT)-binding immunoglobulin that carries the CGAT idiotype. The GAT-VH clone was hybridized to Northern blots of GAT-specific T cell RNAs; there was no evidence of a T cell transcript that hybridized to the GAT-VH probe. The T cells analyzed included: (a) 10 GAT-binding suppressor T cell hybridomas, 6 of which secreted factors with CGAT idiotypic determinants, (b) one GAT-specific helper T cell hybridoma, and (c) two GAT-specific helper T cell lines grown in the absence of feeder cells. The detection limit of the Northern blot analysis was 1-2 copies of a particular mRNA species per cell for the hybridomas and 5-10 copies per cell for the T cell lines. Therefore, we conclude that T and B lymphocytes responding to GAT do not utilize similar VH gene segments. Furthermore, the presence of idiotypic determinants on T lymphocytes does not necessarily imply close structural similarity between T and B cell antigen receptors.
Gamma gene rearrangement and expression in autoreactive helper T cells.