Characterization of cytoadhesion molecules on human monocytes and tissue macrophages

The presence of proteins antigenically related to the GPIIb/IIIa complex expressed on platelets have been investigated on tissue macrophages recovered by bronchoalveolar lavage (lung alveolar macrophages, LAM) or peritoneal lavage (peritoneal macrophages, PM) as well as on monocytes. Polyclonal antibodies (pab) directed against human platelet GPIIb/IIIa and the vitronectin receptor (VnR), and mouse monoclonal antibodies (mab) against human GPIIb, GPIIIa or the GPIIb/IIIa-complex were used. Triton X-100 extracts of bronchoalveolar cells (BAC) (containing 94% LAM) and the ultrasedimentable fraction of cell-free bronchoalveolar lavage (US) reacted with the polyclonal antibodies against the GPIIb/IIIa-complex and the VnR, but only with one (P4) of the mabs. Cell microscopy after immunogold labelling and alkaline phosphatase immunostaining, as well as immunofluorescence using the P4 mab and the polyclonal anti-GPIIb/IIIa clearly demonstrated positive membrane staining of LAM, PM and monocytes. Both BAC and US extracts gave rise to immunoprecipitates in crossed and rocket immunoelectrophoresis using anti-GPIIb/IIIa and anti-VnR. Our data indicate that monocytes and their monocyte-derived tissue counterparts constitutively express GPIIb/IIIa-like antigen(s) on their membrane. The presence of such antigen(s) on tissue macrophages makes it unlikely that platelet contamination is responsible for these findings.