RECEPTORS FOR THE CHEMOATTRACTANTS C5A AND IL-8 ARE CLUSTERED ON THE SURFACE OF HUMAN NEUTROPHILS

We have used high-resolution field emission scanning electron microsco py with backscatter electron imaging to detect immunogold-labeled C5a and interleukin-8 (IL-8) receptors on human blood neutrophils. The rec eptors were labeled with receptor-specific antibodies in combination w ith secondary antibody conjugated to immunogold. When neutrophils were isolated in a ''nonactivated'' state, both of these receptor populati ons were expressed primarily in clusters on nonprojecting domains of t he cell membrane. When these cells were double labeled for C5a and IL- 8 receptors, intermixing of these receptor species in a common cluster was not found. When neutrophils were isolated in an ''activated'' sta te, by mixing the blood with N-formylmethionyl-leucyl-phenylalanine, t he cells were seen to be elongated and ruffled at their anterior pole, but the C5a receptors did not disperse or redistribute on the surface of the peptide-activated cells. Analysis of the distribution of human C5a receptors expressed by transfected mouse L-cell fibroblasts showe d the C5a receptors to be clustered, but expressed on nonprojecting an d projecting domains of the cell surface. These observations provide n ew information on the topographical expression of leukocyte receptors involved in directing cell migration.