As shown in previous in vivo experiment, the amount of polymeric immunoglobulin receptor (pIgR), which mediates the transcytosis of pIgA across epithelial cells, is regulated by lactogenic hormones (PRL and cortisol) during the development of the mammary gland. In the present in vitro study, it appeared that these hormones were insufficient to induce the strong expression of the gene that we observed in vivo. Several papers have shown that IFN-gamma is a strong stimulator of pIgR gene expression in different models. In contrast, nothing is known of the effects of IFN-gamma on pIgR gene expression in the mammary gland. We report here that IFN-gamma strongly increased pIgR mRNA levels through a direct effect on mammary epithelial cells. We show that IFN-gamma activated not only Stat1 but also Stat5 and that expression of the pIgR and IRF-1 genes was strongly correlated following IFN-gamma stimulation in mammary epithelial cells. In conclusion, these experiments enabled the analysis of different types of regulation of pIgR gene expression in the mammary gland and suggest possible co-operation between circulating hormones and locally produced cytokines, leading to pIgR gene expression in the mammary gland.