Effects of supplemental water-soluble β-carotene on IgA induction in the intestine and mammary glands of lactating mice

Passive immunity is critical to the survival and health of neonates, and colostrum or milk is a source of nutrients and immune components for neonates. Immunoglobulin (Ig) antibodies are main immune components in colostrum1), and IgA is the most abundant Ig isotype in mucosal secretions and provides protection against microbial antigens at mucosal surfaces2, 3). Passive immune protection of the newborn gastrointestinal tract is dependent on an active process of IgA antibody-secreting cells (ASC) accumulation in lactating mammary glands of the mother, because IgA antibodies produced from IgA ASC in the mammary glands are secreted into milk4). The β-carotene or vitamin A metabolite, all-trans retinoic acid (RA), plays important roles in the differentiation of immune-competent cells and the proliferation and expansion of lymphocytes5). Supplemental vitamin A and fat-soluble β-carotene (FS-BC) enhance the immune system in neonates5, 6), but β-carotene deficient calves were found to have a higher incidence of diarrhea in the first week of life7). Additionally, supplemental FS-BC may be useful for enhancing colostral IgG1 or IgA concentrations in β-carotene-borderline or deficient Japanese Black cows8, 9). β-carotene is a typical fat-soluble carotenoid, and supplemental FS-BC at 30 and 50 mg/kg in the diet in maternal mice during pregnancy and lactation increased the numbers of IgA ASC in the mammary glands and ileum of lactating mice and enhanced IgA transfer from maternal milk to neonatal mice10, 11). Water-soluble β-carotene (WSBC) is a carotenoid form that has been developed as a food colorant12), but it is not clear whether supplemental WS-BC enhances IgA induction in the small intestine and mammary glands of lactating mice. The present study was conducted to clarify the effects of supplemental WS-BC at 50 mg/kg in the diet on IgA induction in the small intestine and mammary glands of lactating mice and IgA transfer from maternal milk to