The opsonization of protein antigens with complement C3 adducts and their subsequent interaction with complement receptors 1 and 2 on B cells and Follicular Dendritic Cells, drastically increases immunogenicity. Although these processes may equally promote emergence of PD autoantibodies, this potential of CR1/2 has not yet been addressed. Using PD as paradigm autoimmune diseases, A05 will explore the importance of CR1/2 for the emergence of autoimmunity in the EBA mouse model, their role for conversion from inapparent to clinically overt autoimmunity, and their blockade to prevent or halt autoimmune disease.