Dr Jeffrey Weiser, professor of Microbiology and Pediatrics at the University of Pennsylvania School of Medicine and colleagues have found that a healthy population of "good" bacteria in the gut keep the immune system primed to more effectively fight infection from invading ‘bad’ or pathogenic bacteria. Altering the intricate dynamic between resident and foreign bacteria -- via antibiotics, for example -- compromises an animal's immune response, specifically, the function of white blood cells called neutrophils.

Dr Weiser likens these findings to starting a car. It is much easier to start moving if a car is idling than if its engine is cold. Similarly, if the immune system is already warmed up (by relating with ‘good’ bacteria), it can better cope with pathogenic invaders. The implication is that prolonged antibiotic use in humans may effectively throttle down the immune system, so that it is no longer able to deal with new bacterial infections. Certainly, secondary infection is a major complication of antibiotic therapy, especially in hospitals.

The findings also provide a possible explanation for the anecdotal benefits of probiotic therapies because keeping your immune system primed by eating foods enhanced with ‘good bacteria’ may help counteract the negative effects of sickness and antibiotics – what the proponents of probiotic therapy have always claimed.

The study also showed that microbes do affect the innate immune response, via the cellular protein Nod1 which is present within neutrophils. Nod1 is a receptor that recognises parts of the cell wall of bacteria the researchers found that neutrophils derived from mice engineered to lack Nod1 are less effective at killing two common pathogens, Streptococcus pneumoniae and Staphylococcus aureus, than neutrophils from mice with the protein.

Moreover, neutrophils from mice that were raised in a germ-free environment or on antibiotics had a poorer immune response, although their immune function was restored once they were exposed to a normal environment.
The researchers also found that  they could improve immune function by treating both antibiotic-treated mice and human neutrophils with the Nod1 ligand -- which suggests it may be possible to counter the adverse consequences of antibiotics in humans.

Courtesy of Science Daily

First Published Febuary 2010

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