Plain language summary
Food allergies are thought to affect 200 million people worldwide and are most prevalent in children. However, food allergies are also becoming more frequent in the elderly. The authors discuss details of several underlying mechanisms of food allergies in the elderly: 1) Immunosensecence, that is an age-related remodelling of the immune system which favours the development of food allergies. 2) Age related effects on local immune responses, especially on the gastrointestinal mucosa with regards to mucosal tolerance (i.e. tolerance to food allergens). 3) In the elderly, the integrity of the gut epithelial barrier is compromised which contributes to chronic inflammation and allows allergens to penetrate into tissues where they can trigger an immune response. The elderly also commonly have decreased digestive secretions, which leads to proteins not being fully broken down, an additional risk factor for food allergies. 4) Age associated alterations of the gut microbiota may favour the development of food allergies in a number of ways. 5) Nutrient deficiencies, which are common in the elderly, also contribute to the development of food allergies through several mechanisms.
All over the world, there is an increase in the overall survival of the population and the number of elderly people. The incidence of allergic reactions is also rising worldwide. Until recently, allergies, and in particular food allergies (FAs), was regarded as a pediatric problem, since some of them start in early childhood and may spontaneously disappear in adulthood. It is being discovered that, on the contrary, these problems are increasingly affecting even the elderly. Along with other diseases that are considered characteristics of advanced age, such as cardiovascular, dysmetabolic, autoimmune, neurodegenerative, and oncological diseases, even FAs are increasingly frequent in the elderly. An FA is a pleiomorphic and multifactorial disease, characterized by an abnormal immune response and an impaired gut barrier function. The elderly exhibit distinct FA phenotypes, and diagnosis is difficult due to frequent co-morbidities and uncertainty in the interpretation of in vitro and in vivo tests. Several factors render the elderly susceptible to FAs, including the physiological changes of aging, a decline in gut barrier function, the skewing of adaptive immunity to a Th2 response, dysregulation of innate immune cells, and age-related changes of gut microbiota. Aging is accompanied by a progressive remodeling of immune system functions, leading to an increased pro-inflammatory status where type 1 cytokines are quantitatively dominant. However, serum Immunoglobulin E (IgE) levels and T helper type 2 (Th2 cytokine production have also been found to be increased in the elderly, suggesting that the type 2 cytokine pattern is not necessarily defective in older age. Dysfunctional dendritic cells in the gut, defects in secretory IgA, and decreased T regulatory function in the elderly also play important roles in FA development. We address herein the main immunologic aspects of aging according to the presence of FAs.