Infant B cell memory and gut bacterial colonization.

Under normal conditions, the gut microbiota confers health benefits for the host. The microbiota aids in the nutrient processing and contributes to the construction of the intestinal epithelial barrier. Furthermore, animal models demonstrate the importance of stimulation from gut bacteria for a proper maturation of the immune system. In this addendum, we summarize our recent study in which we demonstrate that colonization with Escherichia coli and bifidobacteria in the first 2 months of life was related to higher numbers of CD27-positive memory B cells later in infancy. The numbers of total B cells or CD5(+) CD20(+) B cells, on the other hand, were not related to the bacterial colonization pattern. Thus, the gut microbiota might affect the B cell maturation also in humans, and our study indicates that an early colonization pattern that includes E. coli and bifidobacteria might promote this maturation early in life.