Contribution of the Innate Immune System to Autoimmune Diabetes: A Role for the CR1/CR2 Complement Receptors

B lymphocytes are required for diabetogenesis in nonobese diabetic (NOD) mice. The complement component of the innate immune system regulates B cell activation and tolerance through complement receptors CR1/CR2. Thus, it is important to assess the contribution of complement receptors to autoimmune diabetes in NOD mice. Examination of the lymphoid compartments of NOD mice revealed striking expansion of a splenic B cell subset with high cell surface expression of CR1/CR2. This subset of B cells exhibited an enhanced C3 binding ability. Importantly, long-term in vivo blockade of C3 binding to CR1/CR2 prevented the emergence of the CR1/CR2hi B cells and afforded resistance to autoimmune diabetes in NOD mice. These findings implicate complement as an important regulatory element in controlling the T cell-mediated attack on islet β cells of NOD mice.