The role of probiotics in maintaining immune homeostasis

The immune system is a complex architecture of a collective and coordinated network regulated by various pathways to thermodynamically maintain immune homeostasis. The gut microbiota plays a pivotal role that offers significant stimuli (i.e., gut-brain, gut-lung, and gut-liver axis) for both innate and adaptive immunity, mediating immune and metabolic homeostasis. An intricate correlation between changes in the gut microbiota (dysbiosis) and common diseases/disorders have been attributed to the invasion of pathogens, constant use of antibiotics, and hypercytokinemia—a hallmark of immune homeostasis imbalance. These factors contribute to the severity of inflammatory diseases such as cardiovascular diseases, neurological disorders, and of late the coronavirus disease, Covid-19. Probiotics (Lactobacillus spp. and Bifidobacterium spp.) have been considered as alternative and/or adjuvant therapeutic in restoring the balance of gut microbiota for maintaining immune homeostasis and integrity. The probiotics catalyze dietary fibers and proteins to generate short-chain fatty acids and tryptophan to promote antiinflammatory cytokines, reduce epithelium permeability, reinforcing immunity in the gut mucosa, and regulating the systemic immune response. Herein, we review our overarching understanding of current applications of probiotics in amelioration of gut microbiome, and the improvement of gut barrier function and maintaining immune homeostasis. We also highlight clinical trials on probiotics with reported results for the treatment of inflammatory diseases. Additionally, the looming global Covid-19 pandemic makes it prudent to highlight the role of probiotics in both the innate and adaptive human immune responses, especially amid the Covid-19 vaccination paradigm.