Molecular characterization of the surface of apoptotic neutrophils: Implications for functional downregulation and recognition by phagocytes

We have used a panel of monoclonal antibodies and lectins to examine the pr ofile of surface molecule expression on human neutrophils that have undergo ne spontaneous apoptosis during in vitro culture. Neutrophil apoptosis was found to be accompanied by down-regulation of the immunoglobulin superfamil y members PECAM-1 (CD31), ICAM-8 (CD50), CDB6acde, and CD66b and the integr in-associated proteins CD63 and urokinase plasminogen activator receptor (C D87) that may alter the potential for adhesive interactions. Cellular inter actions may be further influenced by the reduction of the expression of sur face carbohydrate moieties, including sialic acid. Reduced expression of Fc gamma RII (CD32), complement receptor type 1 (CD35) and receptors for pro- inflammatory mediators C5a (CD88) and TNF alpha (CD120b) associated with ap optosis might limit neutrophil responsiveness to stimuli that trigger degra nulation responses. Although many of the receptors we have examined are exp ressed at reduced levels on apoptotic neutrophils, we found that there was differential loss of certain receptors (e,g, CD16, CD15 and CD120b) and inc reased expression of aminopeptidase-N (CD13), Together with our previous da ta showing that expression of certain molecules e,g, LFA-3 (CD58) is not al tered during neutrophil apoptosis, these data are suggestive of specific ch anges in receptor mobilisation and shedding associated with apoptosis. Alth ough reduced expression of CD63 (azurophilic granules) and CR1 (specific gr anules) indicates that granule mobilisation does not accompany apoptosis, a monoclonal antibody (BOB78), that recognises a 90 kDa antigen localised in intracellular granules, defines a subpopulation of apoptotic neutrophils t hat exhibit nuclear degradation yet retain intact plasma membranes. BOB78 p ositive neutrophils were found to bind biotinylated thrombospondin, suggest ing that this mAb defines surface molecular changes associated with exposur e of thrombospondin binding moieties.