Functional characterization of the complement receptor type 1 and its circulating ligands in patients with schizophrenia

We found an increased C1q-CIC level and CR1 expression on blood cells, elevated number of CR1 positive erythrocytes and reduced number of CR1 positive lymphocytes and monocytes in patients compared to controls. No difference in the levels of C3d-CIC between groups was observed. Higher CR1 expression on erythrocytes in CC genotype versus CG+GG for both groups was detected, whereas no difference was observed for other cell populations. Our results indicated that schizophrenia is associated with the increased CR1 expression and C1q-CIC level.Our study for the first time indicated that schizophrenia is associated with the increased CR1 expression and C1q-CIC level. Further studies in other ethnic groups are needed to replicate these findings.Complement receptor type 1 (CR1; CD35; C3b/C4b receptor) is a multifunctional receptor, which is expressed in the majority of peripheral blood cells [1-4], with high affinity to complement components C1q, C3, C4 [5-8] and mannose-binding lectin [9]. Binding of CR1 to opsonic fragments of the complement C3 and C4 components (C3b, C4b, iC3b, and C3dg) and to the complement component C1q attached to immune complexes (IC), foreign or damaged host cells serves to mediate clearance of IC (on erythrocytes (E)) [4,10] and phagocytosis of complement-coated particles (on leukocytes) [3,11,12]. In addition, interaction of CR1 with its ligands plays further roles in regulation of lymphocyte (L) activity by promoting secretion of interleukin (IL)-1α, IL-1β, and prostaglandins [13]. Furthermore, CR1 plays a role in antigen presentation to B cells [12]. In addition to membrane-bound CR1, leukocytes also release soluble form of CR1, which is a potent inhibitor of both the classical and the alternative pathways of complement activation by exhibiting decay-accelerating activity for both C3 and C5 convertases, as well as cofactor activity for factor I-mediated cleavage of C3b and C4b [10,13,14].A number of studies suggest the involvement of alteration