Control of innate-like B cell location for compartmentalised IgM production.

Natural IgM are crucial for early protection against infection and play an important homeostatic function by clearing dead cells. The production of IgM is ensured by a population of B cells with innate-like properties: their response is rapidly activated by innate signals early during the onset of infection. The main reservoir of innate-like B cells (IBCs) are the serous cavities, but their maintenance and activation depends on their relocation to a variety of lymphoid tissues. Recent advances indicate that fat-associated lymphoid clusters (FALCs) and milky spots contribute to local IgM secretion and play a central role in the localisation and regulation of IBC function.