Absence of CD89, polymeric immunoglobulin receptor, and asialoglycoprotein receptor on human mesangial cells

Abstract

IgA nephropathy (IgAN) is characterized by raised serum IgA and predominant mesangial IgA deposits of polymeric nature. The expression of IgA receptor molecules in white blood cells and glomerular mesangial cells has recently attracted much attention in relation to the uptake of IgA by these cells. This study investigates the expression of IgA Fc receptor (FcαR1 or CD89), asialoglycoprotein receptor (ASGPR), and polymeric Ig receptor (pIgR) in cultured glomerular mesangial cells. Using a sensitive nested reverse transcription-PCR, mRNA encoding for FcαR1, pIgR, or the H2 chain of ASGPR was not demonstrated on human mesangial cells. U937, HepG2, and HT29 cell lines, used as positive controls, strongly expressed the FcαR1, ASGPR, and pIgR mRNA, respectively, under similar experimental conditions. Flow cytometry also demonstrated the presence of surface proteins for FcαR1, ASGPR, and pIgR on the respective control cell lines but not on human mesangial cells. Expression of FcαR1 mRNA on cultured U937 cells was upregulated by tumor necrosis factor-α. However, tumor necrosis factor-α, interleukin-1β, or transforming growth factor-β failed to induce the expression of FcαR1 on human mesangial cells. Human serum IgA or secretory IgA bound to human mesangial cells, HepG2, or the U937 cell line in a dose- dependent manner. The binding of purified IgA to human mesangial cells was not blocked by preincubation with human IgG, IgM, orosomucoid, asialoorosomucoid, anti-CD89 antibody (My43), or anti-secretory component antibody. The present study concluded that there was an absence of FcαR1, ASGPR, or pIgR on human mesangial cells. These findings suggest that the predominant binding of human IgA to human mesangial cells is mediated by other mechanisms.