Comparison of abilities of recombinant interleukin-1 alpha and -beta and noninflammatory IL-1 beta fragment 163-171 to upregulate C3b receptors (CR1) on human neutrophils and to enhance their phagocytic capacity.

Both recombinant IL-1 alpha and -beta caused an upregulation of C3b receptors (CR1) on human neutrophils and caused a receptor-mediated enhancement of phagocytosis of C3b.IgG-coated microspheres by these leukocytes. The alpha and beta forms of the recombinant cytokine were of comparable potency regarding CR1 upregulation, although both generally had less than 25% of the potency of FMLP in this respect. Recombinant IL-1 beta was slightly more potent than the alpha form of the cytokine regarding phagocytosis of opsonized microspheres and, again, both forms were less potent than FMLP in causing an enhancement of phagocytosis by neutrophils. The synthetic noninflammatory immunostimulatory nonapeptide corresponding to residues 163-171 of IL-1 beta was completely inert with respect to upregulation of CR1 on neutrophils and the enhancement of phagocytosis by these cells. Thus this domain in the intact IL-1 beta molecule apparently is not involved in CR1 upregulation and the ensuing enhancement in phagocytosis by neutrophils, although it is apparently important in the immunostimulatory activity regarding the proliferation of lymphocytes.