Bifidobacterium longum subsp. infantis regulates Th1/Th2 balance and IgA secretion in neonatal mice with intestinal niches dependence and gender discrepancy

B. longum subsp. infantis, a dominant colonizer of the infant gut, is closely related to the incidence of infant diseases, especially allergies and asthma through the balance of Th1/Th2. This study investigated the abilities of eight different strains of B. longum subsp. infantis to regulate the Th1/Th2 balance and IgA secretion. The strains were gavaged to BALB/C dams in both female (n=8) and male (n=8) mice starting from 1 to 3-weeks-old. Seven strains stimulated dendrites and the expression of macrophage cells. Several strains increased the percentage of T cells, B cells, and T helper (Th) cells in neonatal female and male mice. B. longum subsp. infantis B6MNI promoted Th1 and inhibited Th2-related cytokine and immunoglobulin through the JAK-STAT pathway both in neonatal male and female mice. B6MNI also increased the level of IgA in the colon of male and female mice but only increased the sIgA level in the colon of female mice. Moreover, four strains of B. longum subsp. infantis influenced the total bacterial composition of neonatal female and male mice but only influenced sIgA-coated bacterial composition in the male mice group. These results provide insight into the impact of B. longum subsp. infantis supplementation in early infancy for immune system development and balance