Abstract
Probiotics are defined as live microbial food ingredients that produce several beneficial effects to human health. Probiotic bacteria have been mostly investigated in the prevention of and treatment for different gastrointestinal diseases and allergies. It is not fully clear how probiotics exert their beneficial effects on health, but one of the most probable mechanisms of action is the modulation of immune responses via the mucosal immune system of the gut. Commensal bacteria in the gastrointestinal tract play an integral role in both innate and humoral immunity. It is well established that this protective role can be maintained or modulated by the ingestion of probiotics. More recently, it has been shown that specific probiotic strains can influence the secretion of cytokines to help direct naïve T-helper cells toward either a Th1-dominant, cell-mediated immune response or toward a Th2-dominant, humoral immune response. This paper will review current knowledge of the Th1/Th2 model of humoral immunity as well as introduce how strain-specific probiotics can be used therapeutically to help balance this immune response and therefore help prevent allergy.