Effect of proteolytic enzymes on neutrophil Fc gamma RII activity.

Previous studies have demonstrated that the treatment of neutrophils with proteolytic enzymes markedly reduces the expression of receptor III for the Fc portion of IgG (Fc gamma RIII), but it does not affect the number of Fc gamma RII on the cell surface. In the present study, we analysed the effect of proteolytic enzymes on functional responses of neutrophils induced by immune complexes (IC). Our results showed that treatment with pronase or chymotrypsin markedly increased the binding of IgG-coated erythrocytes (IgG-E) to neutrophils, as well as their capability to display IgG-mediated functions such as antibody-dependent cellular cytotoxicity (ADCC) and chemiluminescence (CL) induced by IgG-E, responses that have been shown to be completely dependent on Fc gamma RII. A similar enhancing effect was observed, in all cases, after neutrophil treatment with neuroaminidase. We also studied the effect of proteolysis on neutrophil activation induced by other types of IC. It was found that pronase and chymotrypsin significantly enhanced CL responses induced by soluble IC (sIC) but did not modify the responses induced by either precipitating IC (pIC) or soluble IC prepared with cationized antibodies (catIC). On the other hand, neuroaminidase significantly enhanced CL induced by either sIC, pIC or catIC. Taken together, our data suggest that the activity of Fc gamma RII can be up-regulated by proteolysis. However, this effect appears to be strongly dependent on the characteristics of the IC employed as stimulus.

Activation of human neutrophils and monocytes induced by immune complexes prepared with cationized antibodies or antigens.

We have recently showed that soluble immune complexes (IC) prepared with cationic antibodies (catIC) induce high levels of neutrophil-mediated cytotoxicity against nonsensitized target cells. In the present work we extended our previous findings by studying the ability of catIC to induce different responses mediated by monocytes and/or neutrophils: monocyte cytotoxicity against nonsensitized target cells, chemiluminescence emission by monocytes and neutrophils, and elastase release from neutrophils. Our results showed that, in all cases, cell responses induced by catIC were markedly higher than those induced by control IC, indicating that cationized antibodies enhance IC ability to trigger phagocytic cell activation. A second aim of the present study was to analyze the effect of antigen cationization on IC properties. Interestingly, we found that all the phagocytic cell responses induced by IC prepared with cationized ovalbumin (OA) were significantly higher than those induced by IC prepared with untreated OA. Our results suggest that the charge of antibody and/or antigen constitutes a critical property that conditions the biological activity of IC. Furthermore, these findings support an important role of cationic antibodies and antigens in the development of inflammatory events associated with certain IC-induced diseases.