Immunofluorescent demonstration of the presence of protein HC on the surface of human lymphocytes

Up-regulation of alpha1-microglobulin by hemoglobin and reactive oxygen species in hepatoma and blood cell lines

alpha(1)-Microglobulin is a 26-kDa glycoprotein synthesized in the liver, secreted to the blood, and rapidly distributed to the extravascular compartment of all tissues. Recent results show that alpha(1)-microglobulin has heme-binding and heme-degrading properties and it has been suggested that the protein is involved in the defense against oxidation by heme and reactive oxygen species. In the present study the influence of hemoglobin and reactive oxygen species (ROS) on the cellular expression of alpha(1)-microglobulin was investigated. Oxy- and methemoglobin, free heme, and Fenton reaction-induced hydroxyl radicals induced a dose-dependent up-regulation of alpha(1)-microglobulin on both mRNA and protein levels in hepatoma cells and an increased secretion of alpha(1)-microglobulin. The up-regulation was reversed by the addition of catalase and ascorbate, and by reacting hemoglobin with cyanide which prevents redox reactions. Furthermore, the blood cell lines U937 and K562 expressed alpha(1)-microglobulin at low levels, and this expression increased up to 11-fold by the addition of hemoglobin. These results suggest that alpha(1)-microglobulin expression is induced by ROS, arising from redox reactions of hemoglobin or from other sources and are consistent with the hypothesis that alpha(1)-microglobulin participates in the defense against oxidation by hemoglobin, heme, and reactive oxygen species.

Alpha 1-microglobulin is mitogenic for guinea pig lymphocytes

Guinea pig alpha 1-microglobulin (alpha 1-m) was found to exert mitogenic effects on guinea pig lymphocytes, i.e. peritoneal exudate lymphocytes (PEL) or T lymphocytes from regional or mesenteric lymph nodes (LNL). On the other hand, spleen T lymphocytes did not respond to alpha 1-m. Stimulation of LNL required the presence of accessory cells. The stimulatory effect was strain-specific: alpha 1-m clearly induced proliferation of lymphocytes from Strain 2 guinea pigs, whereas Strain 13 lymphocytes responded poorly or not at all. Moreover, alpha 1-m inhibited antigen-driven proliferation of guinea pig lymphocytes. None of the effects described were species-specific, e.g. human alpha 1-m exerted similar effects on the guinea pig lymphocytes. These data indicate that alpha 1-m may be involved in the regulation of lymphocyte activation.

Localization of alpha 1-microglobulin (HC protein) in normal human tissues: an immunohistochemical study using monoclonal antibodies

Alpha-1-microglobulin is a low molecular weight (approximately 30 000 d) glycoprotein present in biological fluids. It is heterogeneous in charge. A monoclonal antibody was used to investigate the tissue distribution of the protein in normal human tissues and cell lines by indirect immunofluorescence and immunoperoxidase techniques. The protein was demonstrable in cells of the monocyte-macrophage lineage, in thymus and T cell dependent areas of spleen, lymph node and tonsils. It was detected in several lymphoid or nonlymphoid cell lines but not in peripheral blood lymphocytes. The microglobulin was also detectable in the cytoplasm of hepatocytes. Finally, it was observed in glandular secretions (sudoral glands and mucosal glands of the digestive tract) where it may be associated with IgA. Possible explanations for the highly divergent results previously reported with polyclonal antisera to alpha 1 microglobulin are discussed.

Synthesis of alpha 1-microglobulin by guinea-pig liver

Explants from perfused guinea-pig livers were found to release alpha 1-microglobulin into the culture medium. Tritiated leucine in the medium was incorporated into the protein, suggesting a de novo synthesis of alpha 1-microglobulin by the liver tissue. The size of the protein could not be distinguished from that of purified urinary alpha 1-microglobulin when tested with sodium dodecyl sulfate/polyacrylamide gel electrophoresis. After intravenous injections of tritiated leucine into guinea-pigs, the 105 000 X g pellet of homogenized liver rapidly increased its content of radioactive alpha 1-microglobulin, with a maximum after 20 min. 3H-Labelled alpha 1-microglobulin appeared in serum after a lag phase of 20 min, and by comparing the rate of accumulation with albumin, the synthesis of guinea-pig alpha 1-microglobulin could be estimated to 20 micrograms g liver-1 h-1.

Characterization of alpha 1-microglobulin in human colostrum and milk

The mean concentration of alpha 1-microglobulin in human colostrum and milk, estimated by electroimmunoassay, was found to be about 0.4-0.6 mg/l and 0.1-0.2 mg/l, respectively. Both liquids contained alpha 1-microglobulin in mono- and dimeric forms, while the presence of higher polymeric forms, as characterized in plasma, could not be demonstrated.

alpha 1-Microglobulin from normal and pathological urines

alpha 1-Microglobulin was purified from normal and pathological urines. Significant differences were found in the amino acid compositions of the alpha 1-microglobulin isolated from these two sources. In addition electrofocusing of alpha 1-microglobulin from normal urine gave rise to two peaks of equal intensity with rather acidic isoelectric points (3.8 and 4.2), whilst alpha 1-microglobulin from pathological urine showed two peaks in a 1:5 ratio with less acidic isoelectric points (4.2 and 4.7). Further charge heterogeneity was also observed in the second peaks from both sources. The sugar compositions were also established, as well as the N-terminal sequences of the alpha 1-microglobulin of both peaks isolated from normal and pathological urines.

Production of protein HC by human fetal liver explants

Human fetal lever explants were found to secrete protein HC into the medium in molar amounts comparable to those of albumin, alpha 1-antitrypsin and orosomucoid. Incorporation of a radioactive amino acid from the medium into the secreted protein HC demonstrated de novo synthesis. The secreted protein HC had the same size and electrophoretic mobility as protein HC of plasma and urine and gave a reaction of immunochemical identity with the protein in these biological fluids.

Molecular data on urinary glycoproteins with human leucocyte antigen (HLA) activity

Two glycoproteins characterized by their serological activities (HLA-A9 and HLA-B12), their isoelectric points and their molecular weights were purified from urine from a patient suffering from tubular proteinuria (cystinosis). Their physicochemical properties as well as an important increase of their specific activities during the different purification steps suggested that they behave as human leucocyte antigens (HLA) which had been excreted into urine. Their amino acid compositions and N-terminal sequences were different to those described for HLA solubilized from cultured human lymphoblast cell lines. The N-terminal sequences of the two serologically active glycoproteins were identical to the N-terminal sequence of another recently purified human urinary glycoprotein called human complex-forming glycoprotein. The relationship between HLA, human complex-forming glycoprotein and the serologically active urinary glycoproteins is discussed.