Adaptive and Maladaptive Complement Activation in the Retina

The complement system, commonly associated with innate immune responses to invading pathogens, has been found in the CNS to exert a host of noncanonical functions influential during development and disease. In the retina, local complement expression and activation have been detected in response to injury, and polymorphisms in complement genes have also been linked to the genetic risk for retinal disease. While knowledge regarding the functions, effects, and mechanisms underlying complement in the retina is incomplete, complement expression and activation have been intriguingly linked to both increases and decreases in retinal degeneration in separate contexts and model systems. Here we review the evidence for the varying adaptive and maladaptive contributions of complement and comment on the implications for therapeutic strategies at complement modulation in retinal pathologies.