Low-affinity B cells transport viral particles from the lung to the spleen to initiate antibody responses.

The lung is an important entry site for pathogens; its exposure to antigens results in systemic as well as local IgA and IgG antibodies. Here we show that intranasal administration of virus-like particles (VLPs) results in splenic B-cell responses with strong local germinal-center formation. Surprisingly, VLPs were not transported from the lung to the spleen in a free form but by B cells. The interaction between VLPs and B cells was initiated in the lung and occurred independently of complement receptor 2 and Fcγ receptors, but was dependent upon B-cell receptors. Thus, B cells passing through the lungs bind VLPs via their B-cell receptors and deliver them to local B cells within the splenic B-cell follicle. This process is fundamentally different from delivery of blood or lymph borne particulate antigens, which are transported into B cell follicles by binding to complement receptors on B cells.