Antigen presenting cells (APC) are key regulators of immunity. They are involved in stimulating naïve and effector cells and are critical for orchestrating protective responses to infectious agents as well as aberrant responses to self-antigens. Among APC, B cells are uniquely capable of presenting small amounts of antigen, which they capture and take up through surface immunoglobulin (Ig). The uptake of antigen by B cells is well studied, and so is the loading of peptides onto MHC II, but how these two pathways intersect is less well elucidated. We propose that HLA-DM is a key factor in linking these pathways by interacting with Ig. Here we show that HLA-DM and Ig can be co-precipitated from B cell lines. We also utilized proximity ligation assays and confocal microscopy to show a close interaction between HLA-DM and Ig in fixed B cell lines. In addition, we show by western blot and FACS staining that mutant cell lines lacking HLA-DM have lower levels of Ig than their parent, DM-expressing cell lines. Our data suggest that HLA-DM is involved in linking the antigen uptake and antigen presentation pathways by interacting not only with MHC II but also with Ig.
- Copyright © 2013 by The American Association of Immunologists, Inc.