An Expanded Role for HLA Genes: Encodes a microRNA that Regulates IgA and Other Immune Response Transcripts.

We describe a novel functional role for the locus mediated by its intron-encoded microRNA (miRNA), miR-6891-5p. We show that inhibition of miR-6891-5p impacts the expression of nearly 200 transcripts within the B-lymphoblastoid cell line (B-LCL) COX, affecting a large number of metabolic pathways, including various immune response networks. The top affected transcripts following miR-6891-5p inhibition are those encoding the heavy chain of IgA. We identified a conserved miR-6891-5p target site on the 3'UTR of both immunoglobulin heavy chain alpha 1 and 2 ( and ) transcripts and demonstrated that this miRNA modulates the expression of and . B-LCLs from IgA-deficient patients expressed significantly elevated levels of miR-6891-5p when compared with unaffected family members. Upon inhibition of miR-6891-5p, IgA mRNA expression levels were increased, and IgA secretion was restored in the B-LCL of an IgA-deficient patient. These findings indicate that miR-6891-5p regulates and gene expression at the posttranscriptional level and suggest that increase in miR-6891-5p levels may contribute to the etiology of selective IgA deficiency.