The intestinal mucosal barrier plays a critical role in maintaining the integrity of the gastrointestinal (GI) tract and protecting the body from harmful toxins and pathogens. Nutrition additionally serves as a vital component in maintaining bodily homeostasis. Macronutrients, micronutrients, and specific dietary habits exert profound effects on the immune system. The complex interactions of the immune system reflect a multifaceted, integrated epithelial and immune cell-mediated regulatory system. While several factors can influence the intestinal mucosal barrier and its pro- and anti-inflammatory processes, such as myeloid cell, regulatory T cell (Treg), or intraepithelial lymphocyte populations, there is growing evidence that macronutrients play an essential role in regulating its function. Herein this is a review of the peer-reviewed literature pertaining to dietary effects on mucosal integrity, including intraepithelial lymphocyte populations and immune function. This review is intended to explore the underlying mechanisms by which macronutrients impact and modulate the mucosal immune system.

The emergence and re-emergence of pathogens is a public-health concern, which has become more evident after the coronavirus disease 2019 (COVID-19) pandemic and the monkeypox outbreaks in early 2022. Given that vaccines are the more effective and affordable tools to control infectious diseases, the authors reviewed two heterologous effects of vaccines: the trained immunity and the cross-reactivity. Trained immunity, provided by attenuated vaccines, was exemplified in this article by the decreased the burden of COVID-19 in populations with high Bacille Calmette-Guerin (BCG) coverage. Cross-reactive responses were exemplified here by the studies which suggested that vaccinia could help controlling the monkeypox outbreak, because of common epitopes shared by orthopoxviruses. Although modern vaccination is likely to use subunit vaccines, the authors discussed how adjuvants might be the key to induce trained immunity and improve cross-reactive responses, ensuring that heterologous effects would improve the vaccine’s response.