Binding of avian IgY to type VII collagen does not activate complement and leucocytes and fails to induce subepidermal blistering in mice

Background Epidermolysis bullosa acquisita (EBA) is a severe autoimmune skin disease characterized by tissue-bound and circulating autoantibodies to type VII collagen, the major component of anchoring fibrils. When passively transferred into mice, rabbit IgG against type VII collagen induces Fc-dependent activation of complement, the recruitment of leucocytes into the skin, and subepidermal blistering. In addition to these inflammatory mechanisms, clinical and experimental evidence suggests that antibodies against type VII collagen might induce blisters by disrupting the ligand function of type VII collagen by an Fc-independent mechanism. Objectives To study noninflammatory mechanisms of blister formation in experimental EBA. Methods We generated chicken IgY antibodies directed to recombinant type VII collagen and examined their pathogenic activity using ex vivo and animal models. Results Mice injected with these chicken IgY antibodies showed binding of the antibodies to the dermal-epidermal junction of skin sections. However, IgY antibodies did not fix complement C3 in enzyme-linked immunosorbent assay and immunofluorescence complement-binding assays. In addition, IgY antibodies did not induce dermal-epidermal separation ex vivo. Following their passive transfer into Balb/c mice, chicken IgY antibodies against type VII collagen bound at the dermal-epidermal junction, but, in contrast to rabbit IgG, did not fix complement C3, recruit granulocytes, or induce skin blisters. Conclusion These findings demonstrate that binding of avian IgY to type VII collagen is not pathogenic in vivo and strongly suggest that in experimental EBA, antibodies to type VII collagen induce blisters not by direct disruption of the ligand function of type VII collagen, but rather by an Fc-dependent engagement of humoral and cellular inflammatory factors.