Aging is reported to be associated with decline in oral tolerance induction, which is initiated at the intestinal mucosal surface. Herein, we examined the effect of aging in T cells and cytokines at the intestinal mucosa that might be involved in oral tolerance induction. Frequencies of regulatory-type IEL subsets such as TCRγδ+ and TCRαβ+CD8αα+ were lower in aged mice. Mucosal CD4+CD25+Foxp3+ and CD4+LAP+ T cells increased with aging but activated CD44+CD4+ mucosal T cells also augmented. Production of TGF-β and IL-10 in the small intestine of old mice was reduced. Moreover, the ability of mucosal dendritic cells of aged mice to stimulate TGF-β secretion and differentiation of CD4+LAP+ T cells in co-culture studies also declined with aging. Reduction in these regulatory-type cytokines and T cells may help to explain the decline in susceptibility to oral induction during aging. However, not all mucosal regulatory elements were altered by aging and CD4+CD25+Foxp3+ T cells were especially resistant to changes. Persistence of some mechanisms of regulation might play a critical role in maintaining mucosal homeostasis during aging.

Summary The immature immune system requires constant stimulation by foreign antigens during the early stages of life to develop properly and to create efficient immune responses against later infections. We have previously shown that intake of antigenic dietary protein is critical for inducing maturation of the immune system as well as for the development of T helper type 1 (Th1) immunity. In this study, we show that administration of an amino acid (aa)‐based diet during the development of the immune system subsequently resulted in inefficient control of Leishmania major infection in adult C57BL/6 mice. Compared with mice fed a control protein‐containing diet, adult aa‐fed mice showed a decreased interferon (IFN)‐γ response to parasite antigens and insufficient production of nitric oxide (NO), which is crucial to parasite death. However, no deviation towards Th2‐specific immunity to L. major was observed. Phenotypic analysis of antigen‐presenting cells (APCs) from aa‐fed mice revealed deficient levels of the costimulatory molecules CD40 and CD80, and low levels of interleukin (IL)‐12 produced by peritoneal macrophages, revealing an early stage of maturation of these cells. APCs isolated from aa‐fed mice were unable to stimulate a Th1 response in vitro. Both phenotypic features of T cells from aa‐fed mice and their ability to produce a Th1 response in the presence of mature APCs were unaffected when compared with T cells from control mice. The results presented here support the notion that regulation of Th1 immunity to infection includes environmental factors such as dietary proteins, which provide a natural source of stimulation that contributes to the process of maturation of APCs.

The aim of the present study was to investigate the effect of a protein-free diet in the induction of food allergy and oral tolerance in BALB/c mice. The experimental model used was mice that were fed, since weaning up to adulthood, a balanced diet in which all dietary proteins were replaced by amino acid diet (Aa). The absence of dietary proteins did not prevent the development of food allergy to ovalbumin (OVA) in these mice. However, Aa-fed mice produced lower levels of IgE, secretory IgA and cytokines. In addition, when compared with mice from control group, Aa-fed mice had a milder aversive reaction to the allergen measured by consumption of OVA-containing solution and weight loss during food allergy development. In addition, mice that did not have dietary proteins in their diets were less susceptible to induction of oral tolerance. One single oral administration was not enough to suppress specific serum Ig and IgG1 levels in the Aa-fed group, although it was efficient to induce suppression in the control group. The present results indicate that the stimulation by dietary proteins alters both inflammatory reactivity and regulatory immune reactivity in mice probably due to their effect in the maturation of the immune system.