We report here the successful induction of allotype suppression in homozygous Ighb/b mice (CB20 or C57BL/6) by neonatal injection of T splenocytes from Igha congenic sensitized mice (BALB/c or BC8, respectively). The sensitization of the T cell donors was achieved by two intravenous injections of B splenocytes from Ighb congenic mice. Treated homozygous Ighb/b mice developed, as of 16-24 wk of age, a chronic suppression of Igh-1b expression (IgG2a of Ighb haplotype). The other productions tested (IgM, IgD, and IgA) of Ighb haplotype were unaffected. In vivo treatment with cytotoxic anti-CD4 or anti-CD8 mAb of mice subjected to chronic Igh-1b suppression clearly showed that CD8+ lymphocytes (suppressor or cytotoxic cell) were essential for the maintenance of the suppression. The suppression was indeed abrogated after a 1-wk treatment with anti-CD8 mAb containing culture supernatant, whereas, the anti-CD4-treated mice continued to be subjected to suppression. This anti-CD8 in vivo treatment was shown to have no effect on thymus but to severely reduce the percentages of CD8+ cells in spleen and in peripheral blood without affecting the percentages of CD4+ cells, leading to a large and rapid Igh-1b expression (up to 0.5 mg per ml of serum, the day after the end of the treatment). This suppression abrogation, and thus the Igh-1b expression, was either transient or permanent. When it was transient, a second 1-wk treatment with anti-CD8 mAb containing culture supernatant induced once again a rapid and significant production of Igh-1b (up to 0.3 mg of Igh-1b per ml of serum).

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