DIFFERENTIATION OF ENCEPHALITOGENIC T-CELLS CONFERS RESISTANCE TO AN INHIBITORY ANTI-CD4 MONOCLONAL-ANTIBODY

The anti-CD4 mAb W3/25 inhibits experimental autoimmune encephalomyeli tis (EAE) in Lewis rats by blocking Th cell responses to encephalitoge nic determinants of myelin basic protein (MBP). However, it has yet to be resolved how W3/25 modulates CD4 to inhibit EAE-associated T cell responses. This study revealed that W3/25 profoundly inhibited MBP-sti mulated proliferation by sensitized lymph node cells but only partiall y inhibited the respective response of uncloned and cloned lines of MB P-specific T cells. That is, low concentrations of W3/25 blocked 30 to 60% of MBP-stimulated proliferation, but 100-fold higher concentratio ns did not result in additional inhibition. W3/25 also inhibited MBP-i nduced acquisition of EAE transfer activity, but only in cultures of f reshly isolated lymph node cells and not in cultures of continuously p ropagated T cells. Studies focusing on the GP2.E5 T cell line revealed that the lack of sensitivity to W3/25 in encephalitogenic and prolife rative assays was nevertheless associated with an effective blockade o f MBP-stimulated IL-2 production. Importantly, W3/25 specifically inhi bited antigenic but not mitogenic stimulation of IL-2 production. Reve rse transcriptase/polymerase chain reaction analyses revealed that MBP -activated GP2.E5 T cells produced mRNA for both IL-2 and IL-4, and th at W3/25 selectively inhibited accumulation of IL-2 as compared to IL- 4 mRNA. Thus, GP2.E5 T cells apparently express a IL-4-dependent pathw ay that confers resistance to the inhibitory activity of W3/25. Studie s focusing on two CD4+ T cell hybridomas revealed that W3/25 profoundl y inhibited MBP-stimulated IL-2 production but did not affect the alte rnative response of MBP-induced growth inhibition. Several other hybri ds also mediated MBP-stimulated IL-2 production but did not express CD 4 and were not affected by W3/25. These results indicate that: 1) inte ractions of W3/25 with CD4 do not necessarily block class II MHC-restr icted recognition of MBP; and 2) expression of CD4 is not necessary fo r Ag recognition by several clonotypes of MBP-reactive T cells. Rather , the results of this study are consistent with the concept that W3/25 inhibits transduction of costimulatory signals that are required spec ifically for initiation of IL-2 production. These findings may have im portant implications for understanding the therapeutic potential of an ti-CD4 mAb in autoimmune disease.