The in vivo elimination of CD4+ T cells prevents the induction but not the expression of carrier-induced epitopic suppression.

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Abstract
Injection of mice with an immunogenic dose of carrier (keyhole limpet hemocyanin (KLH)) followed by immunization with hapten-carrier conjugate (TNP-KLH) selectively suppresses anti-hapten antibody response. In this study, the cellular basis of this epitopic suppression and also of the suppression induced by a high dose of carrier were analyzed by in vivo depletion of CD4+ or CD8+ T cell subsets by using mAb. The mAb treatments were performed either at the time of carrier priming or at the time of hapten-carrier immunization. The elimination of CD8+ T cells has not modified the anti-carrier antibody response, whether this treatment was performed at the time of KLH-priming or during TNP-KLH immunization. Moreover, the in vivo treatment with the anti-CD8 mAb did not modify the carrier-induced epitopic suppression induced either by a low immunogenic dose of KLH or by a high dose of this Ag. The elimination of CD4+ T cells at the time of KLH immunization has prevented the induction of a memory response to KLH, clearly establishing that CD4+ T cells are essential in memory B cell development to T-dependent Ag. Moreover, this treatment has totally abrogated the epitopic suppression induced either by low or high dosages of KLH. In contrast, the in vivo elimination of CD4+ T cells after carrier immunization did not abolish the secondary anti-carrier antibody response and did not prevent the expression of epitopic suppression. These data indicate that primed CD4+ T cells are required neither for memory B cell expression nor for the expression of suppression. Finally, once induced, the suppression can be evidenced after in vivo depletion of both primed CD4+ and CD8+ T cells. These data support the view that epitopic suppression is induced through the expansion of carrier-specific B cells and resulted from intramolecular antigenic competition between hapten and carrier epitopes.