Antibiotics in the food supply and as medicines, hand sanitizers, antimicrobial wipes, and herbicides rage war against microbes every day. However, there is an undeniable connection between exposure to microflora (germs) and the function of immune systems. What would the immune system look like without microflora?
Without microflora, the immune system would not exist. The immune system would never mature, self from non-self could not be distinguished, and humans would live in a perpetual state of uncontrolled physiologic cascades. A deeper understanding of the mechanisms at play may inform practitioners how, when, and why to use probiotics for therapeutic effect.
Microflora Trigger Immune Maturation
The purpose of the immune system is to eradicate pathogens while protecting healthy cells and tissues. Innate (or nonspecific) immunity begins to develop in utero, with the creation of mucosal barriers, neutrophils, monocytes, and natural killer cells.1 Adaptive (or specific) immunity only develops with antigenic stimulation—that is, exposure to microorganisms. Microorganisms interact with the developing immune system at all mucous membranes, but particularly at the intestinal mucosa, which interfaces with the gut-associated lymphoid tissue (GALT).2
Neonatal intestinal microflora interacts with the GALT to create immune tolerance of nonpathogenic organisms. Researchers showed that germ-free mice mounted a strong TH2-mediated and IgE-mediated reaction to egg white protein, this allergic reaction could be avoided by intestinal colonization with Bifidobacteria, but colonization was only effective if done during the neonatal stage.3 It appears that early microbial colonization establishes immune tolerance and balances the TH1 and TH2 response.
Neonatal intestinal microflora also promotes the maturation of adaptive immune responses. Researchers showed that human infants colonized with Bacteroides fragilis at 1-month of age (a pattern seen in babies born vaginally) had more IgA-secreting and IgM-secreting cells at 2-months of age than infants who were not colonized with B. fragilis (a pattern seen in babies born via C-section).4,5 Early exposure to healthy microflora initiated strong and mature adaptive immunity.
Microflora Balance Physiologic Cascades
Microflora not only stimulates maturation of the immune system but also modulate immunity throughout life.* One way they do this is by balancing production of counteracting immune cells and cytokines. Just as an absence of neonatal microflora skews immunity toward TH2 dominance, the same is true throughout life.
Studies repeatedly demonstrate that oral administration of probiotics supports immunity in individuals with conditions associated with certain physiologic cascades.*7,8,9
Additional studies demonstrate an ability of probiotics to support the immune response to pathogens: different species and strains of Lactobacillus supported phagocytosis in healthy individuals and immune responsiveness.*10,11
With respect to the power of microflora to trigger immune maturation and modulate immunity throughout life*, the therapeutic applications of oral probiotic therapy become interesting. In a world where C-sections and formula feeding, medications, and poor diets are commonplace, the microbiota suffers. It is time to prioritize probiotic supplementation for those who meet these criteria.
Sarah Cook, ND
Sarah Cook is a freelance medical writer in Westminster, CO. She has a certificate in biomedical writing from the University of the Sciences in Philadelphia, PA and a naturopathic doctorate from the Southwest College of Naturopathic Medicine in Tempe, AZ. She has previous experience in clinical practice, supplement sales, and academics. In addition to writing, she is currently a faculty member at the Nutrition Therapy Institute in Denver, CO.