An adequate immune system is required to prevent diarrhoea in neonates, and IgA provides protection against microbial antigens on mucosal surfaces. Although β-carotene supplementation has been expected to enhance the retinoic acid (RA)-mediated immune response in neonates, the exact mechanism of the enhancement of mucosal IgA production in the small intestine by β-carotene is still unclear. In the present study, we investigated the effect of supplemental β-carotene on the concentrations of IgA, the numbers of IgA antibody-secreting cells (ASC) and the mRNA expressions of IgA C-region, CCL25, retinoid X receptor (RXR) α, retinoic acid receptor (RAR) α and RARγ in the jejunum and ileum of weanling mice. Weanling mice were fed rodent feed or 50 mg/kg β-carotene-supplemented rodent feed for 7, 14 or 21 d. The concentrations of IgA and the numbers of IgA ASC in the jejunum and ileum of mice increased markedly with age, and supplemental β-carotene increased the concentrations of IgA, the numbers of IgA ASC and the mRNA expressions of IgA C-region, CCL25 and RARγ in the jejunum after 14 and 21 d of treatment. Supplemental β-carotene increased the numbers of IgA ASC in the ileum after 14 and 21 d of treatment, but the concentrations of IgA in the ileum were not affected by β-carotene supplementation. The mRNA expressions of RXRα and RARα in the jejunum and those of RXRα and RARγ in the ileum after 21 d of treatment were enhanced by β-carotene supplementation. These results indicate that β-carotene supplementation in weanling mice is effective to enhance mucosal IgA induction in the jejunum or ileum and that the effects are mainly due to the RA-mediated immune response.

Mortality of neonates continues to be a major problem in humans and animals. IgA provides protection against microbial antigens at mucosal surfaces. Although β-carotene supplementation has been expected to enhance retinoic acid-mediated immune response in neonates, the exact mechanism by which β-carotene enhances IgA production is still unclear. We investigated the effect of supplemental β-carotene for maternal mice during pregnancy and lactation on IgA antibody-secreting cells (ASC) in mammary gland and guts and on IgA transfer from milk to neonatal mice. Pregnant mice were fed untreated or 50 mg/kg β-carotene-supplemented diets from 6·5 d postcoitus (dpc) to 14 d postpartum (dpp). Supplemental β-carotene increased the numbers of IgA ASC in mammary gland (P < 0·05) and ileum (P < 0·001), and also mRNA expression of IgA C-region in ileum (P < 0·05) of maternal mice at 14 dpp, but few IgA ASC were detected in mammary gland at 17·5 dpc. IgA concentration in stomach contents, which represents milk IgA level, was significantly higher (P < 0·01) in neonatal mice born to β-carotene-supplemented mothers at 7 and 14 dpp, and IgA concentration in serum, stomach contents and faeces increased (P < 0·001) drastically with age. These results suggest that β-carotene supplementation for maternal mice during pregnancy and lactation is useful for enhancing IgA transfer from maternal milk to neonates owing to the increase in IgA ASC in mammary gland and ileum during lactation.