C‐reactive protein and platelet activating factor complexes induce production and release of interleukin‐1 by human monocytes

Abstract

Stimulation of interleukin‐1 (IL‐1) in peripheral blood monocytes exposed to C‐reactive protein (CRP) and C‐reactive protein‐platelet‐activating factor (CRP‐PAF) complexes was demonstrated in vitro in this study. Significant synthesis of intracellular IL‐1, 2‐5‐fold increases in the number of adherent monocytes as determined by indirect immunofluorescence using rabbit anti‐IL‐1 and goat antirabbit IgG‐fluorescein isothiocynate, was shown. Both CRP alone (10 μg/ml) and especially CRP‐PAF mixture (10 μg CRP/1 ug PAF/ml) showed maximum stimulation of IL‐1 of 41 and 95 cells/10 field examined, respectively. CRP alone examined in a dose‐response study showed optimum stimulation of IL‐1 production at the 1 μg/ml concentration with 57% of monocytes showing fluorescence. CRP at varying concentrations with a constant amount of PAF (1 μg/ml) showed optimum IL‐1 staining monocytes (63%) with CRP at 10 μg/ml (10 pg CRP/l μg PAF). Similar significant enhanced extracellular IL‐1 production by monocytes exposed to CRP and CRP/PAF mixtures was shown by the mouse thymocyte assay. Supernatants of monocytes exposed to CRP (10 μg/ml) or CRP‐PAF (10 μg/l μg/ml) demonstrated mouse IL‐1 synthesis of 92 and 110 stimulation indices in the thymocyte assay, respectively. It is suggested that CRP and especially CRP‐PAF complexes activate macrophage through their appropriate receptors to production of monokines which modulate the immune system. Thus, CRP appears to function nonspecifically in a behavior reminiscent of specific immunoglobulins.