A common concept of the immune system is that of white blood cells putting up a fight against invading pathogens in the bloodstream. Researchers have now detailed a separate but equally important route by which our bodies fight infection—directly inside already infected cells. The team, co-led by Leo James, PhD, and Tyler Rhinesmith, PhD, at MRC Laboratory of Molecular Biology, defined a previously undescribed method of fighting pathogen invaders—and which they called “antibody-directed xenophagy” (ADX)—where cells can digest bacteria and viruses, including Salmonella and adenoviruses, that cross the cell membrane. The scientists found that regulation of ADX is dependent on the intracellular protein, TRIM21, which James’s lab had previously shown protects from viral infection by binding to antibody-coated viruses in the cell cytosol, triggering virus degradation. “People have talked about viral xenophagy before as a sort of concept, but if you look in literature, there aren’t any good examples where people have shown this operating to potently block infection,” said James. “In our single study, we’ve gone from the discovery of something completely unknown [ADX], all the way through molecular mechanism, its function in cells into animals, and demonstrated physiological importance.” The discovery of the ADX pathway may have potential future medical implications. While far more study is needed, the research points to the feasibility that antibody or small molecule therapeutics could be used to treat infections by marking pathogens in the blood so TRIM21 can recognize and jumpstart ADX once they enter cells. James, Rhinesmith, and colleagues reported on…
