Early infiltration of p40IL12(+)CCR7(+)CD11b(+) cells is critical for fibrosis development.
BACKGROUND
Macrophages are heterogeneous and thus can be correlated with distinct tissue outcomes after injury. Conflicting data have indicated that the M2-related phenotype directly triggers fibrosis. Conversely, we hypothesize here that the inflammatory milieu provided by early infiltration of pro-inflammatory macrophages dictates tissue scarring after injury.


RESULTS
We first determined that tissue-localized macrophages exhibit a pro-inflammatory phenotype (p40IL12(+)CCR7(+)CD11b(+)) during the early phase of a chronic injury model, in contrast to a pro-resolving phenotype (Arg1(+)IL10(+)CD206(+)CD11b(+)) at a later stage. Then, we evaluated the effects of injecting macrophages differentiated in vitro in the presence of IFNγ + LPS or IL4 + IL13 or non-differentiated macrophages (hereafter, M0) on promoting inflammation and progression of chronic injury in macrophage-depleted mice. In addition to enhancing the expression of pro-inflammatory cytokines, the injection of M (IFNγ + LPS), but not M (IL4 + IL13) or M0, accentuated fibrosis while augmenting levels of anti-inflammatory molecules, increasing collagen deposition and impairing organ function. We observed a similar profile after injection of sorted CCR7(+)CD11b(+) cells and a more pronounced effect of M (IFNγ + LPS) cells originated from Stat6(-/-) mice. The injection of M (IFNγ + LPS) cells was associated with the up-regulation of inflammation- and fibrosis-related proteins (Thbs1, Mmp7, Mmp8, and Mmp13).


CONCLUSIONS
Our results suggest that pro-inflammatory macrophages promote microenvironmental changes that may lead to fibrogenesis by inducing an inflammatory milieu that alters a network of extracellular-related genes, culminating in tissue fibrosis.
Laboratory of Transplantation Immunobiology, Department of Immunology Institute of Biomedical Sciences IV, University of São Paulo (USP) São Paulo Brazil.
Tarcio Teodoro
TT
Braga
Laboratory of Transplantation Immunobiology, Department of Immunology Institute of Biomedical Sciences IV, University of São Paulo (USP) São Paulo Brazil.
Matheus
M
Correa-Costa
Department of Pediatrics Faculdade de Medicina da Universidade de São Paulo (FMUSP) São Paulo Brazil.
Hatylas
H
Azevedo
Laboratory of Transplantation Immunobiology, Department of Immunology Institute of Biomedical Sciences IV, University of São Paulo (USP) São Paulo Brazil.
Reinaldo Correia
RC
Silva
Laboratory of Transplantation Immunobiology, Department of Immunology Institute of Biomedical Sciences IV, University of São Paulo (USP) São Paulo Brazil.
Mario Costa
MC
Cruz
Department of Cellular Biology-Institute of Biomedical Sciences University of São Paulo (USP) São Paulo Brazil.
Maira Estanislau Soares
ME
Almeida
Laboratory of Transplantation Immunobiology, Department of Immunology Institute of Biomedical Sciences IV, University of São Paulo (USP) São Paulo Brazil.
Meire Ioshie
MI
Hiyane
Department of Pediatrics Faculdade de Medicina da Universidade de São Paulo (FMUSP) São Paulo Brazil.
Carlos Alberto
CA
Moreira-Filho
Department of Cellular Biology-Institute of Biomedical Sciences University of São Paulo (USP) São Paulo Brazil.
Marinilce Fagundes
MF
Santos
Department of Biochemistry-Institute of Chemistry University of São Paulo (USP) São Paulo Brazil.
Katia Regina
KR
Perez
Department of Biochemistry-Institute of Chemistry University of São Paulo (USP) São Paulo Brazil.
Iolanda Midea
IM
Cuccovia
Laboratory of Transplantation Immunobiology, Department of ImmunologyInstitute of Biomedical Sciences IV, University of São Paulo (USP)São PauloBrazil; Laboratory of Clinical and Experimental Immunology, Division of NephrologyFederal University of São Paulo (UNIFESP)São PauloBrazil; Renal Pathophysiology Laboratory (LIM16)Faculty of Medicine, University of São PauloSão PauloBrazil.
Niels Olsen Saraiva
NO
Camara
Collagen; pro‐inflammatory macrophages; renal fibrosis