The human body (when functioning properly) has a pretty incredible inbuilt security system, detecting familiar or novel invaders and launching an attack in the form of an immune response. A discovery deep at sea has thrown into question the all-seeing human immune system, however, as newly discovered "invisible" microbes were found to slip past our defenses without even being detected.
The disconcerting discovery was published in the journal Science Immunology, featuring bacteria found in the world’s largest and deepest UNESCO World Heritage site near the Kiribati islands. Known as the Phoenix Islands Protected Area, it’s one of the most remote spots on Earth – with crew members being closer to those on the ISS than terrestrial humans. Being quite so dramatically out in the sticks means that the marine haven gives scientists the chance to see what life is like in the absence of humans. Joined by a mobile lab and trusty steed SuBastian – a remotely operated vehicle – the team could zoom around collecting samples to culture back onboard.
Over three weeks back in 2017, the team gathered bacteria samples. They wanted to see how they would interact with mammalian cells, using cells of mice and humans to investigate. They did this by removing the lipopolysaccharide shells of 50 different strains of bacteria and putting them in a dish with one of the two mammalian cell groups. Intriguingly, 80 percent of those tested failed to trigger an immune response from the mammalian cells they were bunking with.
The results appear to indicate that these bacteria strains are invisible to the human immune system, eliciting nothing in response to their presence – though it must be considered that their shells were left to run free with isolated cells in a petri dish and not inside a living human being (any volunteers?). As of yet, the researchers are unclear as to the mechanism behind the bacteria’s invisibility cloak, but there did seem to be a correlation between long acyl chains (protrusions that cross a bacterium's lipid layer) and a lack of immune response.
The fact that the bacteria have evolved in a space free of mammals – marine or otherwise – with just 20 percent of those tested stimulating an immune response, suggests that perhaps the efficacy of the human immune system isn’t as universal as we thought.
“The assumption of near-universal bacterial detection by pattern recognition receptors is a foundation of immunology,” wrote the study authors. “However, LPS receptors were unable to detect 80% of deep-sea bacteria examined ... The inability of immune receptors to detect most bacteria from a different ecosystem suggests that pattern recognition strategies may be defined locally, not globally.”