Natural evolution and pathological alterations of lymphoid cell proteins. Immunochemical characteristics of soluble antigens

MB1, a quail leukocyte/vascular endothelium antigen: characterization of the lymphocyte-surface form and identification of its secreted counterpart as alpha 2-macroglobulin

A monoclonal antibody (alpha-MB1) binds to a cell surface marker expressed throughout ontogeny and adult life by vascular endothelial and hemopoietic cells of the quail, with the exception of erythrocytes, although it was raised against the heavy chain of quail immunoglobulin M. In addition to an 80 kDa polypeptide accounting for immunoglobulin mu chain, alpha-MB1 stains intensely a 180-kDa band on Western blots of reduced plasma proteins. We have previously characterized MB1 antigens of quail endothelial cells as glycoproteins of apparent molecular masses ranging from 80 to 200 kDa and provided evidence for the participation of vascular endothelium in the secretion of alpha-MB1-positive plasma components. We demonstrate here that this circulating material is the proteinase inhibitor alpha 2-macroglobulin. Furthermore, the MB1 antigens immunoprecipitated from lymphocytes are shown to be essentially similar to their endothelial counterparts, suggesting that the same molecular complex is expressed by all the elements of the hemangioblastic cell lineage. Finally, the cross reactivity of the alpha-MB1 antibody with immunoglobulin mu chain is confirmed and shown to occur via a carbohydrate epitope.

Leucocyte-associated plasma proteins in leucocytes during disease states, and in leukaemic cells

The concentrations and molecular forms of prealbumin, orosomucoid, albumin, alpha 1-antitrypsin and haptoglobin in leucocytes were studied in patients with alpha 1-antitrypsin deficiency, in acute phase and with leukaemia, by rocket and crossed immunoelectrophoresis. Alpha 1-antitrypsin was the only protein being synthesized by bone marrow cells, blast cells and leucocytes present in the blood during cytotoxic treatment. The other proteins are taken up by the cells. The concentration of alpha 1-antitrypsin in serum and cells was correlated in alpha 1-antitrypsin deficiency and the acute phase, suggesting either that the same signal for synthesis is used in the liver and leucocytes, or that a balance is kept by means of leucocyte uptake. Chronic lymphocytic leukaemia lymphocytes contained only traces of albumin, which may be related to the decreased membrane mobility of these cells. Polycythemia leucocytes, however, contained increased concentrations of all plasma proteins, especially orosomucoid and haptoglobin2 . These two protein forms were found to be markers of mature granulocytes. The cellular concentrations of prealbumin, albumin and transferrin were about 35% of normal in acute myeloid leukaemia cells and no orosomucoid2 and haptoglobin2 was present. Alpha 1-antichymotrypsin was present in a heterogeneous form and the molecular form of alpha 1-antitrypsin (alpha 1 AT4 ) was the same as in monocytes. These findings suggest the existence of a distinct 'AML'-type protein pattern which could be of functional and diagnostic importance.

Leucocyte-associated plasma proteins. Association of prealbumin, albumin, orosomucoid, alpha 1-antitrypsin, transferrin and haptoglobin with human lymphocytes, monocytes, granulocytes and a promyelocytic leukaemic cell line (HL-60)

The distribution of prealbumin, albumin, orosomucoid, alpha 1-antitrypsin, haptoglobin and transferrin, including their electrophoretic heterogeneous variants, was studied in isolated lymphocytes, monocytes and granulocytes and in a human promyelocytic cell line (HL-60) by crossed immunoelectrophoresis. Prealbumin, albumin and transferrin were present in lymphocytes, monocytes and granulocytes, whereas the cellular variants of orosomucoid and haptoglobin were present only in granulocytes. alpha 1-Antitrypsin was present in four electrophoretic variants which were differently distributed among the various cell types. Synthesis of alpha 1-antitrypsin by monocytes, granulocytes and HL-60 cells was demonstrated by 14C-leucine incorporation. The six plasma proteins could not be removed from intact cells by incubation with the respective antibodies at 0 degrees C, or iodinated by lactoperoxidase catalysed iodination at 23 degrees C. They were, however, readily solubilized by freeze-lysis of the cells, suggesting an intracellular localization. Compared to their plasma counterparts none of the proteins differed in their hydrophobic properties but the carbohydrate residues of orosomucoid, alpha 1-antitrypsin and haptoglobin were different. The pattern of disappearance of the proteins from the cells during incubation suggested that the localization of albumin and transferrin in relation to the cells differed from that of the other proteins.