Human alpha-fetoprotein as a modulator of human lymphocyte transformation: correlation of biological potency with electrophoretic variants.

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Abstract
Human .alpha.-fetoprotein (HAFP) isolated by immunoadsorbent column suppressed the mitogenic response of human lymphocytes to phytomitogens [concanavalin A, phytohemagglutinin, pokeweed mitogen], antihuman thymocyte antiserum and the mixed lymphocyte culture. HAFP isolated from the sera and ascitic fluid of 5 hepatoma patients and from fetal liver varied in biological potency over 3 orders of magnitude. Extended agarose gel electrophoresis and crossed immunoelectrophoresis demonstrated 3 molecular species of HAFP. Quantitation of the 3 species revealed a correlation between the relative amount of the most negatively charged species and biological potency. Treatment of HAFP with neuraminidase to completely remove sialic acid residues did not alter the biological potency, but converted the 3 species to 2 species having slower electrophoretic mobilities. Differences in sialic acid content are only partly responsible for the microheterogeneity demonstrated by HAFP, and that variability in another charged moiety is also present. Variation in the relative proportions of the different molecular species of HAFP may be important in the regulation of its immunosuppressive properties.