What are the microbiota and microbiome?
All the microbes living in or on the human body are called the microbiota. The term microbiome refers to the sum of these microorganisms’ genomes.
Both microbiota and microbiome play a central role in the maintenance of the overall health of the host. The microbiome evolves from birth to death being constantly modified and adapted in order to maintain balance with both environmental factors and the hosts immune system1. Thus, as we grow, microbiota and immune system shape the development of each other2.
Our gut hosts 80% of the body´s immune cells. That makes it the main interaction site between our immune system and external microorganisms, as well as the place to educate the adaptative immune system2. This process helps avoid excessive reactions to the microbiota and helps maintain self-tolerance3. The importance of this interaction for the healthy development of the immune system is demonstrated in germ-free mice4.
The role of the gut microbiota in supporting an effective immunity has further been underscored by recent studies. These show that perturbations of gut microbiota can shape the efficiency of cancer immunotherapy, which may explain the variation in clinical responses between individuals5. Similarly, gut microbiota alteration caused by antibiotics has been proven to alter immunity and reduce efficiency of vaccines6 or the effectiveness of anticancer immunotherapies7,8.
Failures in the microbes-immune system regulation can lead to pathological outcomes including allergies or inflammatory disease such as inflammatory bowel disease (IBD)9.
The use of beneficial bacteria (probiotics) is emerging as a new way to manipulate gut microbiota and modulate immunity10. The local and systemic immunomodulatory activity and the mechanism of action of probiotics has been proven for specific probiotic strains and conditions11. Systematic reviews and meta-analysis highlight the strain-dependent immunomodulatory efficiency of bacteria for several diseases or pathologies such inflammatory bowel disease12, multiple sclerosis13, health status of athletes14 or vaccine response15.
In this regard, there is clinical evidence of the immunoregulatory action of specific strains for respiratory tract infections (RTI) and upper respiratory tract infections (URTI) in both children16 and adults17.
A clinical study demonstrated the immunomodulatory effect of L. plantarum DR7, a probiotic strain that alleviates the symptoms of URTI by reducing the duration of nasal symptoms and frequency of infections after 12 weeks of administration17.
In summary, probiotics have been shown to modulate gut microbiota homeostasis straightening local and systemic immunity and helping to maintain a healthy status. Thus, it is suggested that selected probiotic strains could be used as complimentary treatments for specific pathological situations.