CD19 and infection: An elevated risk of infection was observed in patients with active disease and was associated with a B-cell immunodeficiency characterized by low serum IgM levels, poor production of IgM (but not IgG) anti Str. pneumoniae antibodies, low circulating SMB-cells counts, very low circulating MZB, including memory B cells (CD27+/CD19+), MZ B cells (CD27+IgD+/CD19+), and switched memory (SM) B cells (CD27IgD-/CD19+).120,121