In vivo interaction of antibodies with cell surface antigens: a mechanism responsible for in situ formation of immune deposits in the zona pellucida of rabbit oocytes

It was the aim of this study to test the hypothesis that the interaction of antibodies with antigens expressed on the plasma membrane of cells surrounded by a basement membrane or a basement membrane-like structure results in in situ formation of immune deposits. Ovary was chosen for the experiments because we found that a well-characterized protein, angiotensin-converting enzyme (ACE), is expressed in a diffuse pattern on the plasma membrane of mature oocytes. To investigate the events following the in vivo interaction of oolemma-ACE with its antibody, rabbits were injected with goat anti-rabbit ACE gamma-globulin or with Fab fragments of goat anti-rabbit ACE IgG in an ear vein for a maximum of 4 d; they were followed for up to 20 d thereafter. Ovary tissue was studied by immunofluorescence, and immunoelectron, light, and transmission electron microscopy. The results of this study document two new findings: First, that ACE is expressed on the oolemma of rabbit oocytes. Second, that the in vivo interaction of divalent antibodies to this cell surface antigen induces formation of granular immune deposits in the adjacent zona pellucida through a mechanism of "patching" and "shedding" of immune complexes, similar to that occurring in in vitro systems characterized by interaction of plasma membrane receptors with soluble ligands. This mechanism might have importance in the pathogenesis of Heymann glomerulonephritis and of other immunological diseases involving antigens expressed on the plasma membrane of cells.