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Activation of human monocytes by both human β1H and C3b
Authors:R. E. Schopf   K. P. Hammann   O. Scheiner   E.-M. Lemmel     M. P. Dierich
Abstract:We tested whether highly purified human β1H and C3b, two proteins of the alternative pathway of complement activation, could exert an influence on the activity of human monocytes (M[var phi]). The activation process of M[var phi] was assessed by measurements of the respiratory burst in terms of nitro blue tetrazolium (NBT) reduction and by chemiluminescence (CL) tests. In NBT reduction experiments, we found a tendency for β1H to increase NBT reduction, while C3b was found to be rather inhibitory. In CL measurements, both β1H and C3b displayed a stimulatory effect on M[var phi], showing different time- and dose-dependency. For β1H, the maximum stimulation occurred after 15 min, whereas for C3b after 45 min. Zymosan particles which served as a positive control also showed the highest stimulation after 45 min. In dose—response experiments, β1H reached a plateau ranging from 30 to 80 μg/ml. In contrast, using C3b up to 170 μg/ml, no plateau was reached. M[var phi]-depletion and enrichment studies suggested at M[var phi] as being responsible for the stimulatory effects found.

The differences between NBT reduction and CL could possibly be explained by the measurement of only cell-bound reductive potentials by NBT reduction, while in CL measurements, products of the extracellular space are also assessed. Our results suggest that both human β1H and C3b are appropriate stimuli for human monocytes.

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