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

Abstract

Human alpha-fetoprotein (HAFP) isolated by immunoadsorbent column was shown to suppress the mitogenic response of human lymphocytes to phytomitogens, antihuman thymocyte antiserum, and the mixed lymphocyte culture. HAFP isolated from the sera and ascitic fluid of five hepatoma patients, and from fetal liver, varied in biological potency over three orders of magnitude. Extended agarose gel electrophoresis and crossed immunoelectrophoresis demonstrated three molecular species of HAFP. Quantitation of the three species revealed a correlation between the relative amount of the most negatively charged species and biological potency. Treatment of HAFP with neuraminidase to remove completely sialic acid residues did not alter the biological potency, but converted the three species to two species having slower electrophoretic mobilities. We conclude that 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. While characterizing the immunosuppressive effects of human alpha-fetoprotein (HAFP) (1), we noted that HAFP isolates from the serum and ascitic fluid of five patients with hepatoma or from fetal sources varied over three orders of magnitude in their capacity to inhibit in vitro human lymphocyte transformation induced by phytomitogens, antihuman thymocyte antiserum (ATS), and the mixed lymphocyte culture (MLC) (2). The most potent HAFP preparation was that isolated from fetal liver homogenates of stillborn human abortuses of 10-20 weeks' gestation (2). Because HAFP isolates display a microheterogeneity with respect to charge (3, 4), presumably due to differences in sialic acid content, we undertook a study of the effects of such charge differences upon the biological potency of our various preparations. The results indicate that the most negatively charged species of HAFP are those with the greatest capability to suppress the mitogenic responses of human lymphocytes in vitro. We also observed that total desialylation of HAFP preparations does not affect their biological potency, nor does it abolish their microheterogeneity. MATERIALS AND METHODSHuman alpha-fetoprotein was isolated from sera and ascitic fluid of five hepatoma patients (Od., McF., Ho., Cr., and Lu.) by a modification of the method of Hirai et al. (1,2,5). After elution from the immunoadsorbent column, and prior to passage over Sephadex G-150, the HAFP eluate was passed over a second immunoadsorbent column to which the Na2SO4-precipitated globulin fraction of rabbit antihuman serum antibody was attached. HAFP was also isolated from the livers of still-born human abortuses of 10-20 weeks' gestation. The livers were homogenized in phosphate-buffered saline at pH 7.4, centrifuged at 20,000 X g for 1 hr (40), and the soluble liver extract was subjected to the procedures described...

Induction of abortion in mice with a monoclonal antibody specific for suppressor T-lymphocyte molecules

“…One possibility would be cross-reactivity with steroids or steroid receptors that would result in effects similar to those observed by Wright et al (1982) and Rider et al (1987) who used a monoclonal antiprogesterone antibody. Alpha fetoprotein is reported to have immunosuppressive activity (Lester et al, 1976;Murgita et al, 1976) and has a molecular weight of 68 000 similar to that of TsF under alkaline conditions (Figs 1 & 2). However, that the immunoreactive band is not alpha-fetoprotein is evident from the apparent molecular weight under acidic conditions (Fig.…”

A postsynthetic modification of human α-fetoprotein controls its immunosuppressive potency

“…From each of these three sources, a-fetoprotein was isolated by passage over an anti-a-fetoprotein immunoadsorbent column. Trace impurities were removed by subsequent passage over an anti-whole human serum immunoadsorbent column and Sephadex G-150, as described (1,2). In addition, a-fetoprotein was isolated from a homogenate of fetal livers of 15-to 20-week-old stillborn human abortuses.…”

“…We have previously characterized a-fetoprotein microheterogeneity by crossed immunoelectrophoresis in agarose gels and have demonstrated that there is variation of a charged moiety other than sialic acid on the molecule (1). Furthermore, the relative proportion of the most electronegative form of a-fetoprotein in an individual a-fetoprotein isolate correlates with its immunosuppressive potency (1). We now report on the microheterogeneity and immunosuppressive potency of a-fetoprotein isolated from the serum, ascitic fluid, and tumor of a single patient (Gd) dying of a malignant hepatoma.…”

Alpha‐fetoprotein

“…Some of the discrepancies may be due to the existence of microheterogeneous variants of AFP which differ in their biological properties [83].…”