C4B and schizophrenia: Consistent with this prediction, subsequent in vitro work demonstrated increased microglial engulfment of synaptic material in cells isolated from patients carrying schizophrenia risk associated variants (Sellgren et al., 2019) and that human C4A is more efficient at tagging synapses than the C4B isoform which is not associated with schizophrenia risk (Yilmaz et al., 2021).