CELL-SURFACE MOLECULES RELATED TO FACTOR-J IN HUMAN LYMPHOID-CELLS AND CELL-LINES

Factor J (FJ) is a cationic glycoprotein that is able to inhibit in vi tro both the classical and alternative pathways of complement. FJ was purified to homogeneity from human urine by sequential chromatographic steps. To examine the expression of FJ in human cells we obtained mAb s against urine-purified FJ. Preliminary studies by immuno-cytochemist ry revealed that one of the anti-FJ mAbs recognized cell surface compo nents of certain cell lines, such as K562 and U937 cells, so we have f ocused subsequently on the detection of these homologue membrane-bound FJ Ags (FJ-h Ags) in cell lines of lymphoid (Ramos and Jurkat) and mi eloyd (U937 and K562) origin, as well as in peripheral blood cells. Th e flow cytometry analysis of the examined cell lines revealed partial staining ranging from 10% (U937) to 29% (K562) positive cells. Flow cy tometry of peripheral blood cells showed a positive staining in a smal l but consistent population of lymphocytes (mean = 11%, n = 17) but no ne at all on monocytes, granulocytes, erythrocytes, or platelets. Doub le Ab immunostaining of lymphocytes showed that the FJ-h positive popu lation included mainly B lymphocytes (a mean of 63% CD19(+) were FJ-h positive). When we analyzed peripheral blood lymphocytes from a patien t with chronic lymphocytic leukemia B (95% Cb19(+)/CD5(+)), the majori ty of these (55%) bore FJ-h on their surface. Acid strip of these cell s did not abrogate the surface staining, which supports the finding th at the Ag is tightly bound to the membrane. Immunoprecipitation from U 937 cell lysates showed a single 65 kDa band under reducing conditions . FJ-h Ags purified from K562 and U937 cells displayed inhibitory acti vity in the functional EAC14 assay for the classical complement pathwa y, as did urine FJ, and they were recognized immunochemically by five different (one polyclonal and four monoclonal) anti-FJ Abs. In conclus ion, FJ-homologues are present in the membranes of several human cell lines that show functional and antigenic characteristics similar to so luble urine FJ. They are also found in a small subset of peripheral bl ood lymphocytes, mainly B cells. The structural relationship between b oth soluble urine FJ and these membrane-bound FJ-h remains to be estab lished.