CD46 complement regulatory protein also known as CD46 ( is a protein which is encoded by the CD46 gene. CD46(MCP;MIC10) is an inhibitory complement receptor.This gene is found in a cluster on chromosome 1q32 with other genes encoding structural components of the complement system. At least fourteen different transcript variants encoding fourteen different isoforms have been found for this gene.The protein encoded by this gene is a type I membrane protein and is a regulatory part of the complement system. The encoded protein has cofactor activity for inactivation of complement components C3b and C4b by serum factor I, which protects the host cell from damage by complement. The protein encoded by this gene may be involved in the fusion of the spermatozoa with the oocyte during fertilization.