The Leukocyte-Common Antigen (L-CA) Family
The leukocyte common antigen (L-CA, T200, Ly-5 or CD45) consists of a family of abundant membrane glycoproteins of apparent Mr 180–240k present on all lymphoid and myeloid cells but absent from other tissues (1–4). The L-CA shows cell type specific heterogeneity in apparent Mr, glucosylation and antigenicity. L-CA from rat thymocytes gives a single major band on SDS PAGE of 180k Mr, whilst T cells give four bands of 180, 190, 200 and 220k Mr and B cells one broad band at 240k (5) and similar patterns are found on mouse and human leukocytes (2,6). Differences in glycosylation in these forms have been shown with anti-carbohydrate antibodies (7) and by lectin binding (8). Antigenic heterogeneity is revealed by antibodies of the higher Mr bands of L-CA seen on SDS PAGE; e.g. the monoclonal antibody. MRC OX-33 is a marker for B cells and the MRC OX-22 monoclonal antibody recognizes B cells, T cytotoxic cells and about 2/3 of T helper cells but not the remainder of the helper cells nor thymocytes (5). The division of T helper cells using this antibody is of particular interest as these sub-populations have important functional differences (9,10). In addition the MRC OX-22 antigenic determinant is stable to trypsin digestion enabling an antigenically active peptide to be purified by antibody affinity chromatography and sequenced (1).
KeywordsHelper Cell Extra Segment Longe Form Extracellular Part Leukocyte Common Antigen
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- 11.P. Jonson, A. F. Williams, and G. R. Woollett, in: “Hybridoma Technology in the Biosciences and Medicine” Chapter 9, T. A. Springer, ed., Plenum Press (1985).Google Scholar