The Effect of Vitamin A Supplementation on the Intestinal Immune Response in Mexican Children Is Modified by Pathogen Infections and Diarrhea

Abstract

Vitamin A supplementation has consistently reduced infant mortality and the severity of pathogen-induced diarrhea. The mechanism by which vitamin A modulates the mucosal immune response to produce these effects remains poorly defined. To address this issue, stools collected during the summer months from 127 Mexican children 5-15 mo old enrolled in a larger, randomized, double-blind, placebo-controlled, vitamin A supplementation trial were screened for interleukin (IL)-4, IL-6, interferon-gamma (IFN-gamma), and gastrointestinal pathogens. Fecal cytokine values were categorized into 3 levels (undetectable, <median, > or =median). Multinomial regression models were used to determine the probability that vitamin A-supplemented children had higher categorical values of a cytokine than children in the placebo group. Differences in categorical values were also analyzed after stratification by gastrointestinal pathogen infections and diarrheal symptoms. Overall, fecal cytokine categorical levels did not differ between children randomized to the 2 arms. Vitamin A-supplemented children infected with enteropathogenic E. coli (EPEC) had reduced IL-4 and IFN-gamma levels [odds ratio (OR) = 0.3, 95% CI 0.13-0.67 and OR = 0.34, 95% CI 0.14-0.83, respectively] compared with children in the placebo group. Vitamin A-supplemented children had increased IL-4 levels when infected with A. lumbricoides (OR = 12.06, 95% CI 0.95-153.85). In contrast, IL-4 levels increased (OR = 2.14, 95% CI 0.94-4.87) and IFN-gamma levels decreased (OR = 0.51, 95% CI 0.26-0.99) among vitamin A-supplemented children with diarrhea compared with children in the placebo group. These findings suggest that the regulation of the mucosal immune response by vitamin A may depend on the type of enteric pathogen infecting the child and the presence of clinical symptoms.

Associations between Mucosal Innate and Adaptive Immune Responses and Resolution of Diarrheal Pathogen Infections

“…results, given the effect vitamin A has on the immune response (29). This potential bias has been controlled effectively through the inclusion of a variable indicating whether the child was in the vitamin A or placebo group.…”

“…A census was carried out of all children less than 2 years of age living within nine neighborhoods (colonias) that are part of the community of La Magdalena Atlicpac, which is located along the eastern perimeter of Mexico City. Mothers of all children from 5 to 15 months of age were invited to participate in the study as described previously (29,32). Children were excluded if they had diseases causing immunosuppression or any congenital or acquired alteration of the digestive tract, such as chronic diarrhea, that could alter the absorption of micronutrients.…”

“…For this study, we analyzed cytokines from a subsample of children during the summer months of June, July, and August, since this period is when diarrheal E. coli is the most prevalent and when diarrheal rates reach their peak. As such, samples were extracted as described previously (29) and the supernatants were collected, frozen, and stored at Ϫ70°C. These supernatants then were assayed for the chemokines monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8), the proinflammatory cytokines tumor necrosis factor alpha (TNF-␣) and IL-6, the Th1 cytokine gamma interferon (IFN-␥), the Th2 cytokines IL-4 and IL-5, and the T-regulatory cytokine (Treg) IL-10 by an enzyme-linked immunosorbent assay (ELISA) using paired ELISA-specific capture and biotinylated detecting antibody (Ab) (Pierce-Endogen, Rockford, IL, and R&D Systems, Minneapolis, MN).…”

Vitamin A supplementation modifies the association between mucosal innate and adaptive immune responses and resolution of enteric pathogen infections

“…Mothers of all children from 5 to 15 mo of age were invited to participate in the study as previously described (12,13). We targeted this population so that we could determine the effect of vitamin A supplementation on the children's developing immune responses during and immediately after weaning.…”

“…We have addressed these issues by carrying out a randomized, placebo-controlled, double-blind trial concerned with the efficacy of vitamin A supplementation on specific pathogen outcomes in children living in peri-urban areas of Mexico City (12,13). Supplementation in this trial was shown to be associated with distinct pathogen-specific innate and adaptive cytokine responses in stools and with divergent pathogen-specific clinical outcomes.…”