title: Alternative activation of macrophages in human peritoneum: implications for peritoneal fibrosis.
abstract: BACKGROUND
  Depending on the cytokine microenvironment, macrophages (Mϕ) can adopt a proinflammatory (M1) or a profibrotic (M2) phenotype characterized by the expression of cell surface proteins such as CD206 and CD163 and soluble factors such as CC chemokine ligand 18 (CCL18). A key role for Mϕ in fibrosis has been observed in diverse organ settings. We studied the Mϕ population in a human model of peritoneal dialysis in which continuous stress due to dialysis fluids and recurrent peritonitis represent a risk for peritoneal membrane dysfunction reflected as ultrafiltration failure (UFF) and peritoneal fibrosis.
  
  
  METHODS
  We used flow cytometry and quantitative reverse transcription-polymerase chain reaction to analyse the phenotype of peritoneal effluent Mϕ and tested their ability to stimulate the proliferation of human fibroblasts. Mϕ from non-infected patients were compared with those from patients with active peritonitis. Cytokine production was evaluated by enzyme-linked immunosorbent assay (ELISA) in spent dialysates and cell culture supernatants.
  
  
  RESULTS
  CD206(+) and CD163(+) M2 were found within peritoneal effluents by flow cytometry analysis, with increased frequencies of CD163(+) cells during peritonitis (P = 0.003). TGFB1, MMP9 and CCL18 messenger RNA (mRNA) levels in peritoneal macrophages (pMϕ) were similar to those found in M2 cells differentiated in vitro. The ability of pMϕ to stimulate fibroblast proliferation correlated with CCL18 mRNA levels (r = 0.924, P = 0.016). CCL18 production by pMϕ was confirmed by immunostaining of cytospin samples and ELISA. Moreover, CCL18 effluent concentrations correlated with decreased peritoneal function, which was evaluated as dialysate to plasma ratio of creatinine (r = 0.724, P < 0.0001), and were significantly higher in patients with UFF (P = 0.0025) and in those who later developed sclerosing peritonitis (P = 0.024).
  
  
  CONCLUSIONS
  M2 may participate in human peritoneal fibrosis through the stimulation of fibroblast cell growth and CCL18 production as high concentrations of CCL18 are associated with functional deficiency and fibrosis of the peritoneal membrane.
authors.affiliation: Research Unit, Hospital Universitario La Paz-FIBHULP, Madrid, Spain. tbellon.hulp@salud.madrid.org
authors.forename: Teresa
authors.initials: T
authors.lastname: Bellón
authors.forename: Virginia
authors.initials: V
authors.lastname: Martínez
authors.forename: Baltasar
authors.initials: B
authors.lastname: Lucendo
authors.forename: Gloria
authors.initials: G
authors.lastname: del Peso
authors.forename: María José
authors.initials: MJ
authors.lastname: Castro
authors.forename: Luiz S
authors.initials: LS
authors.lastname: Aroeira
authors.forename: Aranzazu
authors.initials: A
authors.lastname: Rodríguez-Sanz
authors.forename: Marta
authors.initials: M
authors.lastname: Ossorio
authors.forename: Rafael
authors.initials: R
authors.lastname: Sánchez-Villanueva
authors.forename: Rafael
authors.initials: R
authors.lastname: Selgas
authors.forename: María Auxiliadora
authors.initials: MA
authors.lastname: Bajo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D049109:Cell Proliferation; D019742:Chemokines, CC / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D005434:Flow Cytometry; D005500:Follow-Up Studies; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy; D008262:Macrophage Activation; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D010530:Peritoneal Dialysis / Q000009:adverse effects*; D056627:Peritoneal Fibrosis / Q000209:etiology* / Q000473:pathology; D010537:Peritoneum / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D010538:Peritonitis / Q000209:etiology* / Q000473:pathology; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D055815:Young Adult
chemical_list: C111792:CCL18 protein, human; D019742:Chemokines, CC; D016207:Cytokines; D012333:RNA, Messenger