C2 and retinitis pigmentosa 1: Quite intriguingly, microarray data from the retina of one RP patient carrying two mutations in the ABCA4 gene showed, among others, an increased expression of complement system genes (complement factor B, complement C2), several cytokines, and cytokine receptors (IL- 6, CXCL10, CXCL2), respectively, indicating a neuroinflammatory process in human RP [24].