Often called the “Second Brain”, the gut holds secrets that have alluded scientists studying it for decades. The gastrointestinal (GI) tract, particularly the small and large intestines, hold millions, if not billions, of bacteria that have formed a mutualistic relationship with us. According to one paper, there are approximately ten times more bacteria in our guts than human cells in our body.
The details of this relationship have yet to be discovered. The human immune system, so adapted to fend off attacking bacteria, seems to ignore the multitude that are inside our guts. This is to our benefit as without gut bacteria, often collectively called the gut flora or microbiome, humans would be unable to digest many of the foods we eat. But how do B and T lymphocyte cells, hallmarks of the bodies adaptive immune system, know not to attack this “good” bacteria? In fact, different subdivisions (serotypes) of Escherichia coli (E. coli) are found naturally in our guts and many have positive effects on us. It is only when we ingest the harmful, but related, serotype of E. coli that we get food poisoning.
There is no difference, from the point of view of the lymphocytes, between the different serotypes of E. coli, save for a few specific proteins (antigens) on the outer membrane, but to our knowledge neither B or T cells have a way to innately know the difference between good E. coli and bad. As more research is being done, more is being discovered and recently, scientists believe they have found a link between our own microbiome and the incurable autoimmune disease multiple sclerosis (MS).
The true cause of MS is unknown but it is characterized by the de-myelination of neurons in the central nervous system by the body’s own immune system. Myelin, a sort of electrical insulator for neurons, is responsible for the quick transfer of electrical signal from one neuron to another. This signal is responsible for all movement and thought as we know it and without myelin, the signals move much slower. Symptoms of MS vary but can be loosely defined as loss of function including numbness, slower reflexes and decrease in coordination. In advanced cases, immobility, difficulty swallowing and difficulty breathing results from the disease. Incurable, treatment often focuses at maximizing the quality of life until the eventual early death, usually within 35 years of the onset of symptoms.
There has been a potential breakthrough. As reported by Scientific American, a research team at the University of California, San Francisco found the levels of two strains of gut bacteria, Acinetobacter and Akkermansia, were elevated in MS-diagnosed patients when compared to healthy controls. Further studies showed that Acinetobacter and Akkermansia, when added to healthy blood, increased the proliferation of helper T cells (Th cells) and decreased regulatory T cells (Treg cells).
Th cells are linked to immune responses as they assist in the creation of antibodies and are critical in other functions linked to reactivity, such as cytotoxicity which is one of the methods the immune system uses to kill foreign targets. Treg cells are crucial in suppressing a hyperactive immune response and have been shown to be crucial in preventing autoimmune diseases.
The researchers, led by Sergio Baranzini, made another interesting connection. The antigens, or protein markers, on the surface of Acinetobacter are very similar to the proteins found on myelin. It is hypothesized that if the immune system developed antibodies, and thus a response, to the antigens found on Acinetobacter, the system could then non-specifically attack self-myelin, leading to MS.
While this conclusion is logical, it is just a hypothesis. What is not clear is just how Acinetobacter and Akkermansia bacteria find themselves in different concentrations in different intestinal systems, why the immune system develops antibodies against them but not against other gut-borne bacteria or if this is the only cause of MS or if there are other, more genetic, underpinnings to the disease.
While the data is still unclear, the paper does lead to a potential new treatment or even cure, to MS. Fecal transplants exist where ones’ natural gut biome is replaced by one that is deemed healthy. While this would not eliminate the antibodies that have already developed against the Acinetobacter and thus myelin, it is potential that it could ease the suffering of those afflicted.
David Csordas is a staff columnist for The Daily Campus. He can be reached via email at firstname.lastname@example.org.