Vitamin A and respiratory tract infections in children

Influence of vitamin A status on the antiviral immunity of children with hand, foot and mouth disease

BACKGROUND & AIMS

Vitamin A (VA) deficiency has been shown to affect antiviral immunity and thus may be related to the progress and outcome of hand, foot and mouth disease (HFMD) in young children. Our objective was to determine whether children with HFMD associated with VA insufficiency displayed a decline in antiviral immunity.

METHODS

450 children with HFMD and 113 non-infected children were included in this study. Dietary investigations were performed using a 24-h dietary questionnaire. The serum concentrations of VA were measured by high-performance liquid chromatography. The serum levels of interferon-α (IFN-α) and enterovirus 71 (EV71) IgM antibodies were detected using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The mean serum VA concentration for all patients was 0.73 ± 0.26 μmol/L, and 237 (52.7%) of them presented low concentrations (≤ 0.7 μmol/L). Both serum concentrations of VA and IFN-α in the patients with complications were significantly lower than in patients without complications (P < 0.01). The decreased concentrations of IFN-α and EV71-IgM were positively related to lower VA levels (correlation coefficient = 0.58 and 0.41, respectively, P < 0.001).

CONCLUSIONS

Most of the children with HFMD presented VA insufficiency, which was associated with their reduced immunity and more severe illness.

Effect of all-trans-retinoic acid on the differentiation, maturation and functions of dendritic cells derived from cord blood monocytes

We investigated the effects of all-trans-retinoic acid on dendritic cells derived from human cord blood monocytes to clarify how vitamin A affects immune function in children. Monocytes were separated from 18 cord blood samples, and dendritic cells were differentiated by culture. The percentage of dendritic cells was markedly lower in all-trans-retinoic acid treated cells than in untreated cells. After exposure to tumour necrosis factor-alpha for 3 days, all-trans-retinoic acid treated dendritic cells showed a reduced capacity to activate alloreactive T cells compared to untreated cells. In addition, all-trans-retinoic acid-treated dendritic cells could drive T cells towards T-helper cell type 2 responses with decreased secretion of interleukin-12, interferon-gamma, and increased production of interleukin-10 and interleukin-4. However, when Ro 41-5253, a selective retinoic acid receptor alpha antagonist, was add to culture, all the above actions were reversed. Thus, all-trans-retinoic acid may act at the first step of the immune response by inhibiting the differentiation of dendritic cells, maturation and induction of the T-helper cell type-2 response. The actions of all-trans-retinoic acid on dendritic cells were mediated through retinoic acid receptor alpha.