One study found an increased density of HLA-DR+ microglia in the hippocampus in patients with positive symptoms (paranoid schizophrenia), which may be linked to increased IL-1β and IL-2 secretion as well as complement-dependent pathways that regulate DA-related brain signaling to modulate monoaminergic neurotransmission (Busse et al., 2012). This evidence concerns the gene IL1B and schizophrenia.