Anti-proliferative action of murine alpha-fetoprotein on activated T-lymphocytes.

Alpha-fetoprotein (AFP) is the dominant serum glycoprotein of fetal life but is expressed only in low nanogram levels in adult sera. A possible explanation for this is that AFP has immunoregulatory properties which may be essential during early ontogeny but unnecessary, if not harmful, in adulthood. The current study shows that the interleukin 2 (IL-2)-dependent division of Lyt 2- T blast cells previously activated in autologous mixed lymphocyte reactions (AMLR) or by stimulation with concanavalin A (Con A) is susceptible to inhibition by AFP. This anti-proliferative activity appears to be independent of any competitive interaction with either IL-2 or I-A antigens and is therefore likely to result from a direct action of AFP on the T cells. These findings support the hypothesis that naturally occurring elevated levels of AFP may be involved in the protection of the conceptus from potentially harmful maternal anti-fetal reactivity and in the establishment and maintenance of T-helper cell tolerance to antigens encountered during early life.