Dietary factors lead to innate immune activation in asthma

The dramatic increase in asthma prevalence in westernised countries in recent decades, and the development of asthma in susceptible individuals who have migrated to a western country, suggests that environmental factors, such as dietary intake, must play a role in the onset and development of the disease. Key features of a westernised diet are low antioxidant intake, high fat intake and chronic metabolic surplus, resulting in obesity. Each of these may be contributing to increased asthma prevalence, due to their ability to modulate the innate immune response. A low antioxidant intake impairs the host's ability to scavenge reactive oxygen species, thereby promoting an NFkappaB-mediated innate immune response, resulting in oxidative damage. A high dietary intake of saturated fat can also activate the innate immune response, as saturated fatty acids can directly activate toll-like receptor 4 (TLR4), which also leads to a NFkappaB-driven inflammatory cascade. Also characteristic of a western diet is chronic metabolic surplus. Continual overeating results in a chronic excess of nutrients. In order to regain metabolic homeostasis, excess energy is stored as adipose tissue, which results in obesity. Adipose tissue is metabolically active and releases proinflammatory mediators such as IL-6, TNFalpha and CRP, as well as adipokines such as leptin, which are central to innate immune pathways. Thus, a western dietary pattern may be highly relevant to activation of the innate immune response, which drives a neutrophilic pattern of airway inflammation, which is increasingly recognised in asthma. Therapeutic strategies aimed at addressing diet-induced innate immune activation are warranted.