The role of B cells in carriage and clearance of Mycoplasma pneumoniae from the respiratory tract of mice

Background. Carriage of Mycoplasma pneumoniae (Mp) in the nasopharynx is considered a prerequisite for pulmonary infection. It is interesting to note that Mp carriage is also detected after infection. Although B cells are known to be involved in pulmonary Mp clearance, their role in Mp carriage is unknown. Methods. In this study, we show in a mouse model that Mp persists in the nose after pulmonary infection, similar to humans. Results. Infection of mice enhanced Mp-specific immunoglobulin (Ig) M and IgG levels in serum and bronchoalveolar lavage fluid. However, nasal washes only contained elevated Mp-specific IgA. These differences in Ig compartmentalization correlated with differences in Mp-specific B cell responses between nose-A nd lung-draining lymphoid tissues. Moreover, transferred Mp-specific serum Igs had no effect on nasal carriage in B cell-deficient ìMT mice, whereas this enabled ìMT mice to clear pulmonary Mp infection. Conclusions. We report the first evidence that humoral immunity is limited in clearing Mp from the upper respiratory tract.