PHYSICAL ASSOCIATION OF COMPLEMENT RECEPTOR-TYPE-3 AND UROKINASE-TYPEPLASMINOGEN-ACTIVATOR RECEPTOR IN NEUTROPHIL MEMBRANES

A previous study has shown that Fc gamma RIIIIB (CD16), an extensively glycosylated glycosyl-phosphatidylinositol-linked neutrophil membrane protein, specifically co-caps with the iC3b R (CR3;CD11b/CD18). This study tests the possible physical interactions of another extensively glycosylated glycosyl-phosphatidylinositol-linked protein, the urokina se-type plasminogen activator receptor (uPAR), with CR3. Receptors wer e labeled using fluorochrome-conjugated F(ab')(2) fragments of an anti -CR3 mAb. In some cases cells were capped using second step F(ab')(2) fragments of an anti-mouse F(ab')(2) antiserum. After 30 min at 37 deg rees C, 65 +/- 4% of the cells exhibited CR3 caps whereas 61 +/- 2% de monstrated uPAR caps. When CR3-capped cells were probed with F(ab')(2) fragments of anti-uPAR conjugated to a distinct fluorochrome, 45 +/- 3% of the cells co-capped uPAR. When uPAR was capped, 48 +/- 2% of the cells co-capped CR3. Similar levels of co-capping were observed using a DNP-conjugated anti-CR3 F(ab')(2) and an anti-DNP second step F(ab' )(2) reagent for capping or using FITC-uPA as a probing reagent. Furth ermore, CR3-uPAR co-capping and/or co-clustering was also observed usi ng anti-CR3 IgM and Mn2+ as integrin aggregation stimuli. Significant co-capping of anti-CD14, anti-CD59, anti-Mo5, anti-HLA, or NBD-PE (a l ipid probe) was not observed. Moreover, CR3 and uPAR co-capping was bl ocked by N-acetyl-D-glucosamine, but not by six other saccharides, sug gesting that a lectin-like site may participate in co-capping. This su ggests that CR3 may regulate adhesive events by several mechanisms, in cluding the regulation of the spatial distribution of uPAR.