[Effect of complement type 1 receptor pre-binding on the phagocytosis mediated by Fc receptor]

As a result of IgG-Fc interaction, sheep erythrocytes sensitized with IgG (E-IgG) are constitutively phagocytosed by resting PMN, although in low numbers. The low efficiency of the system can be improved by opsonization with C3b, since the combination of C3b and IgG makes a powerful opsonic signal. It is accepted that the mechanism of C3b enhancement of IgG mediated phagocytosis is achieved by increasing the adherence of the targets to the phagocyte. Recently, a non-opsonic role for C3b enhancement of IgG mediated phagocytosis has been proposed, in cultured human monocytes. These cells, when adhered on glass surfaces precoated with C3b, showed a marked increase in E-IgG internalization. The effect was dose dependent and it was reproduced utilizing a monoclonal antibody against CR1 (C3b receptor). In the present work we studied the existence of this phenomenon in resting neutrophils and in neutrophils stimulated with two kinds of agents: a phorbol ester (PDBu), which activates the CR1 and fMLP, which increases the expression of this receptor. In previous experiments we determined that the adherence of resting neutrophils on different concentrations of iC3 (which binds CR1 and exerts the same effect that C3b), did not increase the phagocytosis of the E-IgG, using as a control neutrophils adhered on the same concentrations of human serum albumin (HSA) (data not shown).(ABSTRACT TRUNCATED AT 250 WORDS)