Viral complement regulators: the expert mimicking swindlers.

The complement system is a principal bastion of innate immunity designed to combat a myriad of existing as well as newly emerging pathogens. Since viruses are obligatory intracellular parasites, they are continuously exposed to host complement assault and, therefore, have imbibed various strategies to subvert it. One of them is molecular mimicry of the host complement regulators. Large DNA viruses such as pox and herpesviruses encode proteins that are structurally and functionally similar to human regulators of complement activation (RCA), a family of proteins that regulate complement. In this review, we have presented the structural and functional aspects of virally encoded RCA homologs (vRCA), in particular two highly studied vRCAs, vaccinia virus complement control protein (VCP) and Kaposi's sarcoma-associated herpesvirus complement regulator (kaposica). Importance of these evasion molecules in viral pathogenesis and their role beyond complement regulation are also discussed.