TLR7 and systemic lupus erythematosus: DN2 B-cell: DN2 cells, characterized by the absence of CD27, IgD, and CXCR5 expression but the presence of CD11c, are expanded in SLE patients with severe disease, including nephritis and hyperresponsiveness to TLR7 signaling, which leads to plasmablast differentiation and autoantibody production.