Demonstration of the inhibitory effect of human alpha-fetoprotein on in vitro transformation of human lymphocytes

Alpha fetoprotein in the differentiation of neonatal hepatitis and biliary atresia: current status and implications for the pathogenesis of these disorders

Neonatal hepatitis (NH) and biliary atresia (BA) are disorders of early infancy that may be difficult to differentiate. Since surgical therapy can be curative if performed early in the disease course of BA, accurate diagnosis is of great importance. Elevated levels of serum alpha fetoprotein (AFP) do occur in many cases of NH and may be helpful in differentiating this condition from BA. Evidence is presented which suggests that initially BA and NH may be the same disease. The individual host response determines the final clinical outcome and AFP could be the immunoregulatory substance which affects pathological progression from NH to BA.

Detection and separation of two serum factors responsible for depression of lymphocyte activity in pregnancy

Studies using the rosette inhibition test have demonstrated a depression of lymphocyte activity in pregnant mice which occurs as early as 6 hr after fertilization and persists until just before delivery. This depression of lymphocyte activity is induced by two serum factors, the relative contributions of which vary with the time of gestation. The first, a high molecular weight early pregnancy factor, appears within hours of fertilization and then slowly declines in activity as gestation proceeds. The second, a lower molecular weight substance which cross-reacts with antiserum to human chorionic gonadotrophin, appears after the formation of the trophoblast at 4--5 days and persists until parturition.

Human alpha-fetoprotein in the epidermal cells of Bowen's disease

Human alpha-fetoprotein (HAFP) was demonstrated in clusters of atypical cells of an extensive Bowen's disease involving the pubic area. Frozen sections were studied by indirect immunofluorescence using monospecific rabbit anti-HAFP antiserum or purified rabbit anti-HAFP antibody followed by staining with fluorescein isothiocyanate (FITC)-labeled goat anti-rabbit gamma-globulin and by a direct technique using FITC-labeled rabbit anti-HAFP Fab2 fragments. Sections of fetal liver served as positive controls and sections of adult human skin and liver were used as negative controls. Preabsorption of the anti-HAFP antibodies with purified HAFP blocked the fluorescence. This finding adds Bowen's disease to the list of premalignant disorders which possess HAFP as an oncofetal marker of their malignant potential. HAFP might possibly enhance malignant behavior through interference with cellular immunosurveillance mechanisms.

Cellular and genetic restrictions in the immunoregulatory activity of alpha-fetoprotein. I. Selective inhibition of anti-Ia-associated proliferative reactions

Alpha-fetoprotein (AFP), a major alpha-globulin component of fetal and newborn sera, has earlier been shown to exert significant immunosuppressive activity in vitro on T-dependent-immune responses. In the present investigation we have examined the effects of AFP on the recognition and proliferation of T lymphocytes responding in mixed leukocyte culture against histocompatibility-associated alloantigens. Fetal-derived AFP could be shown to exert differential effects on both primary and secondary responses ranging from strong inhibition to occasional enhancement, depending on the stimulating antigens. Proliferative responses against major histocompatibility complex (MHC) I region determinants, mediated predominantly by Ly 1 + cells, were markedly suppressed. Suppression was also observed in responses against Mls locus products, an antigenic system whose recognition requires concomitant recognition of I region gene products on the stimulating cells. In contrast, responses against MHC K or D region determinants, mediated predominantly by Ly 2 + cells, were generally unaffected by AFP. Similarly, non-MHC loci alloantigens distinct from Mls locus products also induced T-cell proliferation which was refractive to suppression by AFP. Because neither Ly 1 + nor Ly 2 + cells responding in this latter situation could be inhibited by AFP, we concluded that the mere fact that a T cell expresses a particular Ly phenotype does not predetermine sensitivity to AFP-induced suppression. In any case, AFP exerts a highly selective suppressive activity on I region-associated immune responses. These data may help to resolve the present controversy over the possibility that AFP has an in vivo relevance as an immunosuppressive agent by pointing out the importance of selecting proper genetic situations for study.

Inhibition of human lymphocyte transformation by human alpha-foetoprotein (HAFP): studies on the mode of HAFP action and the role of HAFP polymorphism

In an effort to explain the mechanism of inhibition of human lymphocyte transformation by human alpha-foetoprotein (HAFP), we sought for, and failed to find, evidence of physical association between HAFP and phytomitogens or antihuman thymocyte antiserum. In addition, 20–40 fold increases in mitogen dose do not reverse the inhibition of lymphocyte transformation by a constant dose of HAFP. The presence of HAFP does not interfere with the attachment of ¹²⁵I-labelled phytohaemagglutinin to the lymphocyte surface.

When analyzed by 2-dimensional crossed immunoelectrophoresis, HAFP isolated from the body fluids of hepatoma patients displays electrophoretic heterogeneity, and demonstrates three charged species of HAFP designated as HAFP-1 (the most cathodal), HAFP-2, and HAFP-3 (the most anodal). The potency of hepatoma-HAFP isolates in inhibiting lymphocyte transformation can be positively correlated with the ratio HAFP-3:HAFP-1 in each preparation. Passage of hepatoma HAFP isolates over CM-cellulose allows the isolation of two distinct HAFP fractions, one at pH 4.95, and the other at pH 5.24. The pH 4.95 CM-cellulose isolate is enriched in the more electronegative HAFP species (HAFP-3) and is, on the average, two times more potent than the pH 5.24 CM-cellulose HAFP isolate. The latter, by comparison with native HAFP, is enriched in the more electropositive HAFP species (HAFP-1).

The structural basis for the charge differences which govern the biological potency of HAFP as a modulator of lymphocyte responses is unknown, but it is independent of HAFP sialic acid content. Inhibition of lymphocyte transformation by HAFP cannot be explained by simple competition between the lymphocyte membrane and HAFP for the mitogen combining sites.

Human alpha-fetoprotein: immunosuppressive activity and microheterogeneity

Purified human alpha-fetoprotein (HAFP) from five patients with hepatoma, one with gastric carcinoma, one with an embryonal cell tumor, and from fetal liver has demonstrated immunosuppressive potencies in vitro which vary over three orders of magnitude. A reversible association of HAFP with the cell surface and a predominant effect on T cells are suggested. No evidence of complex formation between HAFP and mitogen has been found. The microheterogeneity of HAFP has been detailed with crossed immunoelectrophoresis and isoelectric focusing in polyacrylamide gels containing 8M urea, and the immunosuppressive potency of HAFP isolated from a given source can be correlated with the proportion of certain HAFP species contained in it.

Immunosuppressive characteristics of human AFP: effect on tests of cell mediated immunity and induction of human suppressor cells

Murine AFP has been reported to be immunosuppressive in a variety of systems. However, the extent and degree of inhibition has varied in different species and laboratories. Therefore, we have examined the potential suppressive effect of purified human AFP on several in vitro tests of cellular immunity and the potential mechanism of its action. AFP purified from fetal and liver cancer sera significantly inhibited mitogen and antigen-induced proliferative responses but had no effect on lymphocyte E rosetting, MIF production or mitogen induced T cell cytotoxicity to Chang target cells. Purified human AFP induced human suppressor cell activity, capable of suppressing a one-way mixed lymphocyte reaction (MLC). In contrast to Con A induced suppressor cells, AFP induced suppressor cell activity was overcome by mitogen augmentation of the proliferative response in MLC. These data suggest that the inhibition of lymphocyte proliferation by human AFP may be mediated by the induction of a subpopulation of human suppressor cells. Furthermore, mitogen induced cell mediated cytotoxicity was partially inhibited by primary liver cancer serum and completely inhibited by newborn cord serum, in contrast to purified fetal or tumor AFP which had no effect. These data suggest that there are other immunosuppressive factors in fetal and tumor serum which require further characterization. These other serum factors may be responsible for some of the immunosuppressive effects attributed to AFP. Although AFP is unlikely to play a major immunosuppressive role physiologically in vivo, its selective effect on proliferative responses, apparently mediated by suppressor cells, may prove to be a useful pharmacologic probe of the mechanism of these in vitro lymphocyte responses and biological interactions.

Interactions of alpha1-acid glycoprotein with the immune system. I. Purification and effects upon lymphocyte responsiveness

Alpha1-acid glycoprotein (AAG) is a constituent of normal serum which is elevated in concentration in the acute phase of inflammation; its physical and chemical properties have been defined but its biological function is uncertain. In the present study, the effect of AAG on the proliferative response of lymphocytes to several different stimuli was determined. For this purpose AAG was prepared by precipitation of human ascites fluid with sulphosalicylic acid and passage of the supernate through SP-Sephadex; the eluted protein migrated as a single band during immunoelectrophoresis, polyacrylamide gel electrophoresis and chromatography on Bio-Gel-A-1-5 m in 6 M guanidine HCl. This AAG was found to markedly inhibit the proliferative response of human peripheral blood lymphocytes to PHA; it also inhibited blastogenesis induced by Con A and PWM, but to a lesser extent. AAG was not cytotoxic to lymphocytes, and its inhibitory effects were reversed at higher mitogen concentrations. Lymphocytes preincubated with AAG remained less reactive to PHA indicating that, although AAG appeared to react with PHA, its effect was directed predominantly to the cell. Further, AAG markedly inhibited the mixed lymphocyte response, and this effect was directed to the responder cells. Thus, AAG is another acute phase reactant with the ability to modulate lymphocyte responsiveness.

Cellular immune responses in familial medullary thyroid carcinoma

We studied prospectively 46 members of a kindred with familial medullary thyroid carcinoma to determine the importance of possible cellular immune reactivity to tumor antigen. We evaluated in vitro production of macrophage-migration-inhibitory factor and 3H-thymidine uptake by lymphocytes from patients, family members and normal subjects in response to extracts of medullary thyroid carcinoma and normal thyroid tissue. Lymphocytes from 12 of 18 patients with medullary thyroid carcinoma and four of seven patients with C-cell hyperplasia produced migration inhibitory factor or proliferated (or both) in response to tumor antigen. In contrast, cells from only two of 25 normal subjects and two of nine family members not genetically at risk for medullary thyroid carcinoma made migration inhibitory factor and proliferated to tumor antigen. Of particular interest, lymphocytes from six of 12 clinically normal family members genetically at risk for medullary thyroid carcinoma exhibited cellular immune reactivity to tumor antigen.

Inhibition of human lymphocyte transformation by human alpha-foetoprotein (HAFP); comparison of foetal and hepatoma HAFP and kinetic studies in vitro immunosuppression

Five pure isolates of human alpha-foetoprotein (HAFP) from adults with tumours of the li er or stomach, as well as HAFP isolated from foetal liver, inhibit in vitro human lymphocyte transformation induced by phytomitogens, anti-human thymocyte serum, and the mixed lymphocyte culture. Foetal HAFP produces 50% inhibition at concentrations of 1-5 mug/ml. The HAFPs isolated from tumour-bearing adults are 1-3 orders of magnitude less potent (50% inhibition achieved at approximately 20, 130, 500, and 2000 mug/ml, respectively). In order to achieve maximum inhibition HAFP must be present at the time of mitogen addition; pre-exposure of lymphocytes to HAFP, followed by washing, does not result in lymphocyte suppression. The inhibiting effect of HAFP cannot be overcome by a ten-fold increase in mitogen concentration implying that HAFP does not act by simple competition with the lymphocyte membrane for the mitogen combining site. HAFP may play an immunoregulatory role during foetal development.

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

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.