HLA-G Is Widely Expressed by Mast Cells in Regions of Organ Fibrosis in the Liver, Lung and Kidney

We previously demonstrated that mast cells expressing HLA-G are associated with regions of hepatitis C virus-induced liver fibrosis. Here, we aimed to determine whether HLA-G expression in mast cells is specific to viral etiology, the liver, or to the general process of fibrosis. We enumerated HLA-G(+) cells and mast cells by the immunohistochemistry of (i) liver blocks from 41 cases of alcoholic cirrhosis, (ii) 10 of idiopathic pulmonary fibrosis (IPF), and (iii) 10 of renal fibrosis. The nature of the HLA-G(+) cells was specified by multiplex immunofluorescence using software. More than half of all HLA-G(+) cells were mast cells in fibrotic areas of alcoholic cirrhosis and IPF. In the kidneys, subjected to fibrosis, the HLA-G(+) cells were indeed mast cells but could not be counted. Moreover, in certain cases of the liver and lung, we observed a number of cellular nodes, which were secondary or tertiary follicles, in which HLA-G was highly expressed by B lymphocytes. In conclusion, HLA-G(+) mast cells could be observed in the fibrotic regions of all organs studied. Previous studies suggest a protective role for HLA-G(+) mast cells against inflammation and fibrosis. The observed follicles with B lymphocytes that express HLA-G may also reinforce their antifibrotic role.