A study comparing multi-drug resistant-TB patients with healthy controls revealed decreased rates of non-class switched memory (IgD+CD27+) B-cells and circulating plasma cells (CD19dimIgD−CD38+++CD27++), with increased numbers of circulating type-1 transitional (IgD+CD38++), CD69+ and Toll-like receptor 9 (TLR9)+ B-cells in the peripheral blood of multi-drug resistant-TB patients (131). This evidence concerns the gene TLR9 and tuberculosis.