Macrophage production and activity of innate immune proteins C1q, C1r, and C1s are modulated in response to molecular patterns

Abstract

Abstract Pattern recognition receptors of the complement system, such as C1q, are vital for clearance of foreign and altered-self targets. C1q has a dual role in vivo: activating the inflammatory classical complement pathway via C1 complex formation (C1qC1r2C1s2) and opsonization in the absence of C1r and C1s which is anti-inflammatory. We hypothesize that macrophages encountering foreign targets will increase levels of C1 subunits to activate C1 and mount an inflammatory response while macrophages encountering damaged-self targets may only increase C1q production to promote anti-inflammatory responses and clearance. Human monocyte derived macrophages (HMDM) were incubated with LPS, E. coli bioparticles, oxLDL, apoptotic cells or polarized into M1 or M2 HMDMs. RNA was isolated for qPCR and supernatant for Luminex protein analysis, ELISA, and C1(q) hemolytic titers. Data show that M1 HMDM increase C1r and C1s mRNA, and produce higher levels of active C1 than M0 HMDM. In contrast, there is no change in gene or protein expression of C1 subunits in M2 HMDM. HMDM treatment with foreign targets revealed a trend of increased C1r and C1s mRNA, and decreased C1q mRNA, but not at the protein level. Treatments with damaged-self targets varied; as hypothesized, C1q gene and protein expression increases in response to apoptotic cells, however there are no substantial changes in treatments with oxLDL. Significant levels of active C1q, but not C1, were detected in response to LPS, oxLDL, and apoptotic cells. Data suggests there is modulation of C1 subunit production and activity in response to different targets. C1q production in the absence of C1r and C1s may be important in resolving inflammation during clearance of apoptotic cells, thus avoiding autoimmunity.