Murine Complement Receptor Types 2 and 1 (CR2/CR1, CD21/CD35) are products of alternative splicing from a single gene. Mouse CR2 (CD21) is composed of 15 short consensus repeats (SCRs), whereas mouse CR1 (CD35) is identical to CR2 but contains an additional 6 N-terminal SCRs. CD35, also known as CR1, binds the complement fragments C3b, iC3b, C4b, and iC4b. CD21/CD35 are primarily expressed on B lymphocytes, mast cells, follicular dendritic cells, macrophages, and activated granulocytes.
