Environment-dependent down-modulation of CD45 cell surface expression on polymorphonuclear cells

CD45, a transmembrane protein tyrosine phosphatase, regulates important cell functions. Its involvement in clearing tissues from dead or dying cells by polymorphonuclear cells (PMNs) is unclear. Therefore, in this study the influence of exogenous factors (e.g., temperature and phagocytosis) on the CD45 expression on PMNs (in patients with lupus erythematosus (LE) vs. controls) was analysed by flow cytometry. The data showed a significant down-regulation of CD45 at 4 degrees C in controls, but not on LE-PMNs. In the presence of targets, CD45 was significantly decreased (P<0.00002). Substrate-dependent down-regulation was greater in the presence of nuclei than in the presence of dead cells(68.98%+/-2.28% vs. 47.89%+/-2.75%; P<0.002), and on LE-PMNs than on control-PMNs (45.93%+/-4.92% vs. 53.65%+/-2.2%). Target pretreatment with anti-dsDNA antibody-containing serum resulted in a lower CD45 expression compared to treatment with normal serum. This effect was more pronounced on PMNs of LE patients than on those of controls. Phagocytosis was inversely correlated with CD45 expression (P<0.0007). These data suggest that phagocytic clearance of cellular debris by PMNs may modulate the function of the effector cells, and that anti-dsDNA antibodies apparently enhance the phagocytic clearance.