Tag Archives: infections

Europeans picked up a customized immune system by having sex with Neanderthals

Researchers have discovered that people of European and African descent have very different immune responses to infections. They believe these traits could be the result of modern humans breeding with Neanderthals after leaving Africa.

Image credits Paul Hudson / Flickr.

Sometime between one hundred to a few tens of thousands of years ago, as modern humans migrated out of Africa, they met strange peoples which weren’t completely like them, but not too different either — the Neanderthals. So, naturally, they had sex with them.

The genes we acquired in that exchange may be responsible for a whole range of diseases, but it’s possible they gave our ancestors the means to better adapt to their new environment. Scientists studying the immune system of humans today have found that people of European descent have significantly different immune responses from their African counterparts — a direct consequence of the exchange, they believe.

The finding could explain why Africans generally have more robust immune systems than Europeans, but also why they’re more predisposed to certain autoimmune conditions.

“I was expecting to see ancestry-associated differences in immune response but not such a clear trend towards an overall stronger response to infection among individuals of African descent,” says University of Montreal geneticist and paper co-author Luis Barreiro.

Barreiro’s team examined samples taken from 175 American patients, roughly half and half of African and European ancestry. They extracted macrophages from their blood — white cells that kill pathogens by “eating” them — and infected the cells with Listeria and Salmonella. They let them go about their business for 24 hours, then analyzed them.

The cells retrieved from the African group had reduced the bacterial growth three times faster than the European group thanks to a stronger inflammatory response. That’s a definite plus when combating infections, but the team points out it’s a double edged sword.

“The immune system of African Americans responds differently, but we cannot conclude that it is better,” Barreiro said, “since a stronger immune response also has negative effects, including greater susceptibility to autoimmune inflammatory diseases such as Crohn’s disease.”

The team also examined the genetic makeup of the cells’ active genes, and found a link between the European sample and Neanderthal DNA — but didn’t find any similar link in the African sample.

The team says that when early humans migrated into Europe around 100,000 years ago, they encountered a continent already colonized by the Neanderthal. Finding traces of their DNA in modern European subjects suggests that the two species actively bred with each other. It makes sense, too. The new genes would have offered our ancestors an evolutionary edge in Europe, where environmental conditions were very different from those in Africa. A lower inflammatory response would also make more sense in the colder climate compared to Africa’s sweltering heat, which promotes infections.

“Our results suggest that the immune systems of African- and European-descended individuals have evolved to better respond to the specific needs imposed by their specific environments,” Barreiro told Live Science.

“What is advantageous in one context is likely to be detrimental in another.”

Too much of a good thing

A separate study also found a lower inflammatory tendency in monocytes against bacterial and viral threats in people of European descent compared to those from Africa. The study included 200 participants from France. The team, led by Lluis Quintana-Murci from the Institut Pasteur, also tied the differences to Neanderthal-like genes in the European participants. In broad lines, the results are the same. The French team also suggests that a powerful inflammatory response could actually be dangerous in Europe, so this effect could have provided an inherent evolutionary benefit — weeding out the more inflammatory-prone genes over time.

“Reducing immune inflammatory responses is a way to avoid autoimmunity, inflammatory, and allergic reactions,” Quintana-Murci told ResearchGate.

“Finding that reduced immune responses has conferred an advantage highlights the tradeoff between recognising pathogens while avoiding exacerbated, aberrant reactions that can be also harmful for the host.”

Both studies say more work needs to be done before we understand where these differences stem from. But it could help us develop things like personalized treatments or medications tailored for certain ethnicities’ needs.

“There is still much to do,” says Barreiro. “[Genetics] explains only about 30 percent of the observed differences in immune responses. Our future studies should focus on other factors, emphasising the influence of the environment and our behaviour.”

Barreiro’s and Quintana-Murci’s studies are published in the journal Cell.

Super-strong, drug resistant bacteria evade detection net

Drug resistant bacteria (immune to almost all antibiotics) are dreaded by patients and physicians alike. Finding them in hospitals is bad enough as it is, but failing to detect them is even worse – it can result in a dramatic outbreak.

Tests for antibiotic resistance in bacteria require regular updates to remain effective as microbes evolve. Image credits: CDC

This is why patients with bacterial infections are typically screened using automated lab tests that uncover the pathogen’s identity, as well as its susceptibility to various (common) antibiotics. Since germs constantly evolve and often become more resistant to some drugs, the responsible organization (FDA in the US) periodically updates the rules for the machines used to perform these tests. But there’s a big problem.

[READ] Antibiotics of the future might come from the bottom of the oceans

The FDA rules have still not been fully adopted in tests for carbapenem-resistant Enterobacteriaceae, or CRE. CRE is a family of gram-negative bacteria that are nearly immune to the carbapenem class of antibiotics, considered the “drug of last resort” for such infections. Many doctors believe CRE to be the newest and most dangerous superbugs, so not detecting them would be a huge problem!

These germs don’t give up easily

The cycle that typically happens is that as the FDA updates its susceptibility criteria, manufacturers must upgrade the screening machines and resubmit them to the FDA for approval. But at the moment, none of the manufacturers have incorporated the latest criteria for all three major types of carbapenem antibiotic – which means that most hospitals are using outdated, potentially dangerous medical screening equipment. This means that CRE cases might go undetected – and this spells big problems.

“It is sad this is a man-made problem,” says Janet Hindler, a clinical microbiologist at the University of California, Los Angeles.

Another problem is that the resistant bacteria category keeps getting larger and larger – and this is also a man-made problem; one of the main reasons is that more detailed studies on antibiotic effects on the human body (as opposed to a Petri dish in a lab) have shown that the threshold for antibiotic resistance in the body is lower than once thought. Another reason is that many types of resistant bacteria have emerged since various antibiotics were first approved.

Meanwhile, Europe is doing a little bit better – Europeans have removed at least one hurdle to getting its own up-to-date resistance categories. The expert body that recommends the classifications, the European Committee on Antimicrobial Susceptibility Testing, also sets the criteria for the European Medicines Authority – which reduces a lot of bureaucracy and saves a lot of time.

But the problem of antibiotic-resistant germs is getting more and more challenging, and it’s becoming harder and harder to keep it under control.

Via Nature.