News ID: 153789
Published: 0238 GMT June 24, 2016

Microorganisms affect transplant acceptance, rejection

Microorganisms affect transplant acceptance, rejection

Bacteria that colonize the body play a significant role in its function, with researchers now finding in experiments with mice that the type of bacteria present in both donors and recipients can affect the success of a transplant.

Researchers at the University of Chicago found treating both donor and recipient mice with antibiotics before a transplant increased the amount of time skin grafts survived on the rodents, according to a recently published study, UPI reported.

Success rates for transplants of organs exposed to the environment, such as skin, lungs and intestines, are worse than those for internal organs such as hearts and kidneys, researchers say, because of the range of bacteria that may colonize them.

The bacteria play a role in triggering immune responses, which can cause transplants to be rejected and is the reason most transplant patients are often prescribed immunosuppressant drugs after surgery.

In the cases of mice in the study, researchers found treating them with antibiotics killed some types of bacteria, allowing the transplants to survive longer.

The results of the study suggest that while some bacteria induce faster rejection of a transplant, those that survive antibiotics do not have that ability, according to Dr. Maria-Luisa Alegre, a professor of medicine at the University of Chicago.

"We have evolved to cohabit effectively with our microbes, and they are very beneficial," Alegre said.

"We need them. They make vitamins we need. They digest foods we can't digest and help maintain our health by poising our immune system for fighting infections. So we have to be careful with anything that's going to alter that balance."

For the study, published in the Journal of Clinical Investigation, the researchers tested skin grafts between groups of mice that had been treated with antibiotics for ten days before the transplant or not treated with antibiotics at all, as well as with groups raised in germ-free conditions.

Mice treated with antibiotics had more successful grafts, lasting 53 days, compared to 27 days for mice that did not receive the drugs.

The researchers also tested the effects of fecal microbiota transplants from the antibiotic and untreated groups of mice on germ-free mice, finding germ-free mice receiving fecal transplants from untreated mice rejected skin grafts more quickly than those receiving fecal transplants from antibiotic treated mice.

The researchers tested this with heart transplants, as well, finding the results were similar between the groups of mice, with transplants surviving longer for mice receiving fecal transplants from antibiotic-treated mice.

While the researchers write in the study that types of bacteria left behind by antibiotics allow for the success of transplants, they are still unsure of the types of bacteria speed transplant rejection and those that do not.

"In terms of the total number of bacteria that are present, it's the same before and after antibiotics. But instead of 1,000 species, let's say you have just 500 after treatment," Alegre said.

"So it's not the bacterial load that makes the difference, it's the composition of the bacterial community."


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