A role for lipid rafts in C1q-triggered O2- generation by human neutrophils.

Calreticulin, a candidate C1q receptor, was shown recently to be present on the surface of human neutrophils in association with glycosylphosphatidylinositol (GPI) anchored proteins, particularly CD59. In this study, we show that antibodies to CD59, as well as to every other GPI-anchored protein tested, inhibited the C1q-triggered release of O(2)(-) from PMN. Methyl beta cyclodextrin (M beta CD) treatment of the cells to disrupt lipid rafts also prevented C1q-triggered O(2)(-) production. beta(2) integrin-dependent co-stimulation is required for O(2)(-) production from PMN, however M beta CD had no effect on LFA-1 or Mac-1-mediated adhesion, soluble iC3b binding to PMN, or spreading and migration, all of which suggested that PMN integrin function remained intact. Flow cytometric analysis of PMN treated with M beta CD showed upregulation of PMN granule-associated integrins and a corresponding increase in integrin activation-reporter epitopes, in contrast to the decreased expression of GPI-anchored antigens. These data support a model where lipid rafts and their associated GPI-anchored proteins are critical for C1q-triggered O(2)(-) production, consistent with a model where calreticulin serves as the C1q receptor for O(2)(-) production from PMN.