RECONSTITUTION OF ANTIBODY-DEPENDENT PHAGOCYTOSIS IN FIBROBLASTS EXPRESSING FC-GAMMA RECEPTOR-IIIB AND THE COMPLEMENT RECEPTOR-TYPE-3

In this study, we test the hypothesis that co-expression of both the c omplement receptor type 3 (CR3; CD11b/CD18) and Fc gamma receptor type IIIB (Fc gamma RIIIB) (CD16) are sufficient to mediate Ab-dependent p hagocytosis. To explore the roles of these receptors in a simple and w ell-defined in vitro system, stable transfectants of fibroblasts expre ssing either CR3, Fc gamma RIIIB, or the combination of CR3 and Fc gam ma RIIIB were generated. Cells not expressing either receptor, but exp osed to the transfection protocol, were used as controls. Cell surface expression of CR3 and/or Fc gamma RIIIB were confirmed by using both flow cytometry and epifluorescence microscopy. The cell lines were ana lyzed for their ability to bind and internalize opsonized erythrocytes . Cells expressing both CR3 and Fc gamma RIIIB were able to both bind and phagocytose IgG-coated erythrocytes. In contrast, cells expressing CR3 only were able to phagocytose yeast, but not to bi nd nor phagocy tose Igc-coated erythrocytes. Similarly, cells expressing Fc gamma RII IB only were able to bind IgG-coated erythrocytes, but not to phagocyt ose either the erythrocytes or yeast. These studies demonstrate that, although CR3 does not participate in Ab-dependent. recognition, it can complement the function of Fc gamma RIIIB to effect Ab-dependent phag ocytosis. These studies also suggest that one mechanism for glycosylph osphatidylinositol-linked proteins to mediate intracellular functions is through interactions with transmembrane proteins.