ABSTRACT

This chapter reviews the understanding of the interaction of Complement receptor 2 (CR2) with C3d and its other ligands. CR2 acts as a B-cell co-receptor for antigen receptor-mediated signal transduction that results in markedly enhanced cellular activation. Support for a critical role of CR2 in the immune response has been provided by results in mice that are deficient in CR2/ Complement receptor 1 (CR1). In mice, CR2 is encoded along with the larger receptor CR1 by the Cr2 gene, which produces both proteins through alternative splicing of a common mRNA. In addition to amplifying adaptive immune responses to foreign antigens, several studies have suggested that CR2 and/or CR1 also play a role in maintaining B-cell tolerance to self-antigens. Despite the solution of the cocrystal structure of CR2 with C3d, there is evidence that supports the hypothesis that certain features of the solution structure may well be different from the static ligand-bound structure observed in the co-crystal structure.