Role of Probiotics in Stimulating the Immune System in Viral Respiratory Tract Infections: A Narrative Review

Abstract

Viral respiratory tract infection (RTI) is the most frequent cause of infectious illnesses including the common cold. Pharmacological solutions for treating or preventing viral RTIs are so far limited and thus several self-care products are available in the market. Some dietary supplements such as probiotics have been shown to modulate immune system function and their role in reducing the risk and the course of RTIs has been investigated extensively within the past decade. However, the mechanism of action and the efficacy of probiotics against viral RTIs remains unclear. We searched PubMed, Google Scholar, and Web of Knowledge for pre-clinical and clinical studies investigating the effect of probiotics on respiratory virus infections, immune response, and the course of upper and lower respiratory tract illness. The literature summarized in this narrative review points out that specific probiotic strains seem effective in pre-clinical models, through stimulating the immune system and inhibiting viral replication. Clinical studies indicate variable efficacy on upper respiratory illnesses and lack proof of diagnosed viral infections. However, meta-analyses of clinical studies indicate that probiotics could be beneficial in upper respiratory illnesses without specific etiology. Further studies aiming at discovering the mechanisms of action of probiotics and clinical efficacy are warranted.

Effects of a Lactobacilli Probiotic on Reducing Duration of URTI and Fever, and Use of URTI-Associated Medicine: A Re-Analysis of a Randomized, Placebo-Controlled Study

“…On the other hand, probiotics may exert immunomodulatory effects in viral and bacterial infections through modulation of cytokine levels [ 21 , 22 ]. Particularly, DR7 reduced pro-inflammatory cytokine IFN-γ and increased anti-inflammatory cytokines IL-10 in plasma, and targeted the tryptophan-5HTT-kynurenine pathway [ 12 ] via downregulation of IDO and TDO [ 13 ].…”

Probiotic Effects against Virus Infections: New Weapons for an Old War

“…Although viruses can cause a wide variety of infections in different organs and systems of the human body, viruses were split, for this literature review, into three groups: Respiratory viruses, digestive viruses, and other viruses. Acute viral respiratory infections are among the leading causes of death worldwide, accounting for more than 4 million deaths per year [ 11 ]. In addition, these viruses are a leading cause of pediatric morbidity and mortality worldwide because of the immature immune system of the babies.…”

“…In addition, these viruses are a leading cause of pediatric morbidity and mortality worldwide because of the immature immune system of the babies. On the other hand, the elderly are more susceptible to serious complications due to their weakened immune system [ 11 ].…”

“…These viruses spread easily between humans due to airborne transmission through aerosols, causing outbreaks that are very difficult to control [ 30 ]. Viral respiratory pathogens belong to various virus families, so RNA-containing viruses are more significant: Picornaviridae , Orthomyxoviridae , Paramyxoviridae , Reoviridae , Coronaviridae , and DNA-containing viruses, such as Adenoviridae and Parvoviridae [ 11 , 31 ]. Individuals can also be infected simultaneously with multiple viruses, and in some cases, multiple viruses have synergistic effects against host health [ 11 , 27 ].…”

“…Among different strategies to prevent and reduce viral infections, adequate nutrition, including nutrients or food ingredients that enhance and potentiate immune response, are useful alternatives to reduce the number of infections and their severity. One nutritional strategy used in recent years to improve human immunity and reduce the ability to be infected is the intake of probiotics [ 11 ].…”