Leucocyte-associated plasma proteins

Abstract

The distribution of prealbumin, albumin, orosomucoid, α₁-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. α₁-Antitrypsin was present in four electrophoretic variants which were differently distributed among the various cell types. Synthesis of α₁-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°C, or iodinated by lactoperoxidase catalysed iodination at 23°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, α₁-anti-trypsin 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 the other proteins.

Key Words:

• α₁-antitrypsin synthesis
• crossed immunoelectrophoresis
• lactoperoxidase labelling of proteins
• leucocytes
• molecular heterogeneity