Effect of human alpha-fetoprotein on native and in vitro-stimulated NK activity

We have examined the effect of human alpha-fetoprotein (h-alpha FP), at concentrations ranging from the physiological to pathological circulating levels, on the native and alpha IFN- and IL2-boosted NK activity of normal peripheral blood lymphocytes (PBL). The cytotoxic function of unstimulated PBL was unchanged after a 16 hr incubation with 200 to 8000 ng/ml h-alpha FP. By contrast, this treatment significantly reduced the responsiveness of PBL to the NK-enhancer factors IFN and Interleukin 2. Optimal inhibition was observed when cells were pre-incubated with h-alpha FP before being stimulated with IFN. The sensitivity of PBL to the h-alpha FP mediated inhibition was restricted to the very early times (30 min) of incubation with the stimulating agents.