The Ancestral Roots of B Cells
In an October 2006 issue of Nature Immunology, certain B cells of basal vertebrates (like fish and amphibians) were shown to be capable of phagocytosis, a function usually associated with cells of the innate immune system. The authors postulate that these phagocytic B cells represent the ancestral history shared between macrophages and lymphocytes. B cells may have evolved from macrophage-like cells during the formation of the adaptive immune system.
B cells in humans (and other vertebrates) are nevertheless able to endocytose antibody-fixed pathogens, and it is through this route that MHC Class II presentation by B cells is possible, allowing Th2 help and stimulation of B cell proliferation. This is purely for the benefit of MHC Class II presentation, not as a significant method of reducing the pathogen load.
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