Since T cells play a critical role in collagen-induced arthritis (CIA), CD4+ T cell hybridomas were derived from DBA/1 mice immunized with bovine type II collagen (CII). The hybrid clones selected were Thy-1-2+, CD4+, CD8-, T cell receptor (TcR) alpha beta + and produced interleukin-2 in response to CII peptides presented by I-Aq molecules. The clones were collagen type-specific and recognized CII from many species except the mouse. More precisely, the reactivity was directed against the immunodominant cyanogen bromide-cleaved fragment CB11(II). Analysis of the TcR carried by the T cell hybridomas showed that they used identical V alpha and J alpha (V alpha BMB, J alpha 20) gene segments and two distinct V beta (V beta 1 and V beta 4) associated with the J beta 2.5 gene segment. Interestingly, the junctional regions were highly conserved in structure and length. These findings may indicate a strong in vivo selection by the antigen for a particular combination of both alpha and beta chains of the TcR. Inoculation of irradiated anti-CII T cell hybrids into DBA/1 mice, before priming with CII, altered the course of the disease resulting in either a long-lasting suppression or an exacerbation of CIA whereas a control CD4+ hybridoma with an unrelated specificity did not influence the development of arthritis. However, the regulatory effect of anti-CII T cell clones was unpredictable, suggesting that the TcR structure may not solely account for the modulation of CIA and that T cell vaccination is not a reliable method for inducing suppression of CIA.