α-Fetoprotein induces suppressor T cells in vitro

Abstract

THE ability of α-fetoprotein (AFP) of mouse or human origin to suppress certain T cell-dependent immune reactions in vitro is well documented^1–4. These findings on a tumour-associated embryonic substance⁵ have potentially important implications as to our understanding of the maternal–foetal immunological relationship⁶, the development of immune capabilities in the foetus and newborn⁷, and of certain diseases⁸ where immunological hyporeactivity and elevations in AFP often occur concomitantly. The mechanism(s) through which AFP is exerting its immunoregulatory influence is largely unknown, however, previous studies¹ have shown that AFP must be added at the initiation of antigen-stimulated spleen cell cultures for maximal inhibition of primary antibody synthesis to occur. Continued presence of AFP in the cultures for 8–12 h was sufficient to maintain suppression in an AFP-free environment for at least 5 d in vitro¹ and 10 d in vivo using adoptive transfer experiments (unpublished). These observations suggested that AFP may inhibit immune responses indirectly by activating regulatory suppressor cells. Here we report that AFP does indeed induce the formation of highly efficient suppressor T cells with capacity to inhibit helper T cells, but with no effect on B cells responding to thymus independent antigens.