Plasmacytoid dendritic cells are scarcely represented in the human gut mucosa and are not recruited to the celiac lesion

Celiac disease (CD) is a chronic small intestinal inflammation precipitated by gluten ingestion. According to case reports, interferon (IFN)-alpha administration may induce development of overt CD. Plasmacytoid dendritic cells (PDCs) were thought to be the source of IFN-alpha and promote a T helper type 1 response leading to lesion formation. Surprisingly and contradicting to earlier findings, PDCs were described as the main antigen-presenting cells (APCs) in human duodenal mucosa and particularly in CD. Here we show that when assessed by flow cytometry and in situ staining, PDCs represent <1% of APCs in both normal duodenal mucosa and the celiac lesion. Low levels of IFN-alpha were detected in the celiac lesion assessed by western blot, reverse transcriptase (RT)-PCR, and immunohistochemistry. In four cell populations sorted from the celiac lesion (based on their expression of HLA-DR and CD45), we found that equally low levels of mRNA for IFN-alpha were distributed among these cell populations. Together, these results suggest that relatively small amount of IFN-alpha, produced by a variety of cell types, is present in the celiac mucosa. IFN-lambda, a type III IFN important in intestinal antiviral defense, was produced mainly by APCs, but its expression was not increased in the celiac lesion.