Good Bacteria Keep Immune System Primed To Fight Future Infections

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" Good " Bacteria Keep Immune System Primed To Fight Future Infections, According

To Penn Study

28 Jan 2010

Scientists have long pondered the seeming contradiction that taking

broad-spectrum antibiotics over a long period of time can lead to severe

secondary bacterial infections. Now researchers from the University of

Pennsylvania School of Medicine may have figured out why.

The investigators show that " good " bacteria in the gut keep the immune system

primed to more effectively fight infection from invading 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.

Senior author Weiser, MD, professor of Microbiology and Pediatrics,

likens these findings to starting a car: It's 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, it can better cope with pathogenic invaders. The implication

of these initial findings in animals, he says, is that prolonged antibiotic use

in humans may effectively throttle down the immune system, such that it is no

longer at peak efficiency.

" Neutrophils are being primed by innate bacterial signals, so they are ready to

go if a microbe invades the body, " Weiser explains. " They are sort of 'idling',

and the baseline system is already turned on. "

Weiser and first author e, PhD, a postdoctoral fellow in the Weiser

lab, published their findings last week in Nature Medicine.

" One of the complications of antibiotic therapy is secondary infection, " Weiser

explains. " This is a huge problem in hospitals, but there hasn't been a

mechanistic understanding of how that occurs. We suggest that if the immune

system is on idle, and you treat someone with broad-spectrum antibiotics, then

you turn the system off. The system is deprimed and will be less efficient at

responding quickly to new infections. "

The findings also provide a potential 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.

Researchers have for many years understood that most bacteria in the body are

not " bad. " In fact, humans (and mice) have a symbiotic relationship with their

resident microbes that significantly impacts, among other things, metabolism and

weight homeostasis. As shown in this study, microbes also affect the innate

immune response, via the cellular protein Nod1.

Present within neutrophils, Nod1 is a receptor that recognizes parts of the cell

wall of bacteria. Weiser and his colleagues 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

that do express the receptor.

In addition, neutrophils from mice that were raised in a germ-free environment

or on antibiotics were likewise diminished in their immune responses, but this

effect was not permanent: Re-exposure of these mice to a conventional

environment (that is, one containing normal bacteria) restored immune function.

The team provided evidence for a potential mechanism for these observations by

showing that bacterial cell wall material could be detected in the blood of

normal mice, and that it influences neutrophils in the bone marrow. Finally, the

team demonstrated they could improve immune function by treating both

antibiotic-treated mice and human neutrophils with the Nod1 ligand - a finding

that suggests it may be possible to counter the adverse consequences of

antibiotics in humans.

The study was funded by the US Public Health Service.

Source: Kreeger

University of Pennsylvania School of Medicine

Article URL:

http://www.medicalnewstoday.com/articles/177355.php

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