C3 and multiple sclerosis: Interestingly, while both C1q and C3 fragments are seen in postmortem human brain tissue from multiple sclerosis (MS) patients [77], recent studies have reported that C3, but not C1q, is required for loss of retinogeniculate synapses and visual acuity in multiple MS-relevant animal models [78], suggesting that complement activation by classical pathway (involving C1) is not the only means of tagging synapses for engulfment (see below).