Role of CD4+ and CD8+ cell subsets during amplification of natural T cell activity against IgG2ab in Igha mice and during induction of IgG2ab allotype suppression in Igha/b mice.

Transfer into F1 Igha/b mice of splenocytes from Igha mice sensitized once against B cells from an Ighb congenic strain induces total, chronic, and IgG2ab (IgG2a of the Ighb haplotype)-specific allotype suppression in these recipients. We previously demonstrated that both the CD4+ and CD8+ T subsets were necessary for inducing suppression, but that CD8+, cells by themselves were sufficient for maintaining suppression. We have studied the suppression induction capacity of different mixtures of CD4+ and CD8+ subsets obtained by in vitro cytotoxic treatment of T splenocytes from normal or sensitized Igha mice, and we have established that suppression induction requires the cooperation between CD4+ and CD8+ populations, both of which have to be IgG2ab specific. In addition, Igha mice were sensitized in the absence of CD4+ or CD8+ cells by in vivo cytotoxic treatment performed before and after the sensitization in order to obtain an IgG2ab-specific CD4+ population that has arisen in the absence of CD8+ cells, and vice versa. We found that only IgG2ab-specific CD4+ cells from anti-CD8-treated mice (T'sens CD4+) had the ability to induce suppression in F1 Igha/b hosts. Nevertheless, the real effector cells in this suppression model display the CD8+ phenotype, as in vivo cytotoxic anti-CD8 treatment of Igha/b recipients of T'sens CD4+ abrogates the suppression induction capacity. Taken together, these results show that T'sens CD4+ have an important capacity to recruit CD8+ anti-IgG2ab effector cells from precursors that have been transferred with them into Igha/b hosts. These precursors are actually derived from the T'sens CD4+ cell preparation, because we have recently demonstrated that suppression is maintained by donor T cells throughout the recipient's life. CD4+ cells can have their anti-IgG2ab activity amplified only by means of target cells (i.e., B cells from Ighb congenic mice), whereas, in the absence of CD4+ cells, and despite the presence of target cells, CD8+ cells seem unable to acquire this amplified activity.