Faculty Bibliography

In mammalian species and in the oldest of multicellular animal forms, NSAIDs inhibit cell activation, apparently in the absence of effects on PG biosynthesis. Thus, an alternative hypothesis can be proposed to account for the antiinflammatory effects of these drugs. Clearly, at low doses aspirin and most of the newer NSAIDs inhibit the biosynthesis of PGs from arachidonic acid, and stable PGs have been shown to mediate fever, hyperalgesia, vasodilation (edema), and several interleukin-1-dependent responses. At high doses, however, aspirin, sodium salicylate, and the newer NSAIDs (at antiinflammatory doses) inhibit non-PG-dependent processes, such as the activity of a variety of enzymes, proteoglycan synthesis by chondrocytes, transmembrane ion fluxes, and chemoattractant binding. These effects are most likely due to the capacity of aspirin-like drugs to insert into the lipid bilayer of plasma membranes, where they disrupt normal signaling events and protein-protein interactions. The ability of NSAIDs to thereby inhibit the activation of inflammatory cells such as the neutrophil may contribute to the antiinflammatory properties of this class of drugs

The iC3b receptor (CR3) is required for neutrophil adhesive functions, including homotypic aggregation. Because stimuli that enhance neutrophil adhesion also induce up-regulation of surface CR3, it is widely held that these two responses are causally related. We have dissociated CR3 display (immunofluorescence) from CR3 function (aggregation). Neutrophils isolated at 4 degrees C and rewarmed to 37 degrees C up-regulated surface CR3 twofold, but did not aggregate. The kinetics of FMLP-induced CR3 up-regulation were discordant with those of aggregation. In the absence of extracellular divalent cations, CR3 expression increased twofold after exposure to FMLP, but neutrophils did not aggregate. FMLP elicited 3.5-fold more aggregation than the ionophore A23187, yet less than one-half as much CR3 up-regulation. 3 mM sodium salicylate inhibited aggregation 55 +/- 4%, but had no effect on CR3 up-regulation. Conversely, 1 mM tetracaine completely inhibited CR3 up-regulation, while significantly enhancing aggregation. Neutroplasts expressed CR3, but did not up-regulate the receptor; in contrast, FMLP induced CR3-dependent aggregation of neutroplasts. We conclude that, although constitutive surface CR3 is required for neutrophil aggregation, the up-regulation of CR3 is neither necessary nor sufficient to promote cell-cell adhesion

Whether homotypic neutrophil aggregation depends on the quantitative increase of gp165/95 molecules (Mac 1, CR3) recruited to the cell surface during activation was studied using mAb of the CD11b group that recognize distinct epitopes encoded by the alpha-subunit of this glycoprotein. After the addition of antibody MN41, neutrophils did not aggregate in response to a chemoattractant, FMLP. Blockade of preexisting surface gp165/95 by mAb MN41, followed by removal of the excess antibody from the mixture, was used to show that the molecules of gp165/95 newly expressed in response to stimulation by a chemoattractant were incapable of effectively mediating the induced cell-cell interactions of aggregation. Flow cytometry studies confirmed that binding of unlabeled antibody MN41 did not block further increases in surface expression of gp165/95 after stimulation with FMLP. These data suggest that molecules of gp165/95 exhibit two functionally distinct forms, one, present on the surface of freshly isolated neutrophils, that becomes competent to mediate the aggregation response upon activation by a stimulus and a second form that can be translocated to the cell surface by the stimulus but is greatly diminished if not lacking in the ability to participate in that aggregation event