Specific types of gut microbes are associated with reduced risk of heart transplant rejections, according to a new study.

By Maria Arvaniti 

If you or your close ones are suffering from heart disease, then you know that a transplant may sometimes be the only ticket to survival. Organ rejection, however, makes things difficult. Transplant recipients usually take strong medications to prevent their immune system from rejecting the new organ. Still, around 10% of patients die in the first three years following the operation, as their bodies react strongly to the foreign tissue that could have saved their lives1.

The link between a successful heart transplantation and the gut is our immune system.

But now, scientists are revealing that bacteria in our gut may predict weather a transplantation will be successful or not2. Researchers from the University of Maryland School of Medicine, US, the University of Hohenheimt in Germany and Université Côte d’Azur in France have just showed that the link between a successful heart transplantation and the gut is our immune system.

Jonathan Bromberg, professor of surgery, microbiology and immunology at Maryland School of Medicine, and his colleagues wanted to study how gut microbes could delay or prevent the rejection of transplants.  They thought that bacteria from pregnant mice could be useful. That’s because the mother’s immune system is suppressed during pregnancy, in order to prevent any attacks against the growing embryo.

When mice that got a non-matching heart transplant received gut bacteria from pregnant mice, all responded well to their transplanted heart – 100% success!

The team showed that when mice that got a non-matching heart transplant received gut bacteria from pregnant mice, all responded well to their transplanted heart – 100% success! What great news, especially considering that those who received bacteria from “normal” mice or mice with colitis – a disease that causes gut inflammation – the transplanted heart got rejected in most cases.

Common gut bacteria are behind successful transplantations

Now, you may be wondering what kinds of your own gut bacteria could help with an organ transplant. To answer exactly this, the team took a closer look into which specific types of bacteria could be behind these promising results. For the most positive transplant outcomes, Bifidobacterium pseudolongum was linked, whilst bacteria belonging to the Mucispirillum and Desulfovibrio types were most associated with organ rejections.

For the most positive transplant outcomes, Bifidobacterium pseudolongum was linked, whilst bacteria belonging to the Mucispirillum and Desulfovibrio types were most associated with organ rejections.

Pinpointing these specific bacteria types could be a useful tool in the hands of physicians, who could potentially use them to predict patient responses to organ transplantation. Nonetheless, you could be asking: how does this happen? One possible explanation is that gut bacteria are able to come in contact with our immune cells on the intestinal wall. From there, they can tune our immune responses. “It’s a way to turn down the volume knob on the immune system,” says Bromberg.

It’s a way to turn down the volume knob on the immune system”, says Bromberg.

The scientists think that these results could be relevant for transplantations of other organs as well. It seems our microbes are there for us and all our other organs, old and new. 


References:

  1. Lund, L. H. et al. The registry of the International Society for Heart and Lung Transplantation: thirty-first official adult heart transplant report–2014; focus theme: retransplantation. J. Heart Lung Transplant. 33, 996–1008 (2014).
  2. Bromberg, J. S. et al. Gut microbiota–dependent modulation of innate immunity and lymph node remodeling affects cardiac allograft outcomes. JCI Insight 3, (2018).