Our work illustrates that the host response to the gut microbiome, including relationships between IgA+ and total gut bacteria, is dysregulated in early-stage MS, building on previous work where decreased proportions of IgA + gut bacteria were associated with high levels of physical disability and recent clinical relapses.18,42 We observed a significantly reduced proportion of IgA-coated gut bacteria at the onset of clinical MS despite similar levels of secreted fecal IgA between patients with MS and controls. Here, CD79A is linked to myeloid sarcoma.