In a new study published in the journal Microorganisms, a team of researchers from the UK, the Netherlands and Germany tested how mammalian immune cells responded to peptides containing two amino acids that are commonly found in carbonaceous meteorites. The immune response to these alien peptides was less efficient than the reaction to those common on Earth. The findings suggest extraterrestrial microorganisms could pose an immunological risk for space missions aiming to retrieve samples from planets and moons.
“The discovery of liquid water at several locations in the solar system raises the possibility that microbial life may have evolved outside Earth and as such could be accidentally introduced into the Earth’s ecosystem,” said study senior author Professor Neil Gow from the Medical Research Council Centre for Medical Mycology at the University of Exeter and the Aberdeen Fungal Group in the Institute of Medical Sciences at the University of Aberdeen, and colleagues.
“Unusual sugars or amino acids have been found in high abundance on carbonaceous meteorites.”
“It is therefore conceivable that extraterrestrial microorganisms might contain proteins that include rare amino acids.”
“We asked whether the mammalian immune system would be able to recognize and induce appropriate immune responses to putative proteinaceous antigens that include these rare amino acids.”
In the study, conducted in mice, the scientists examined the reaction of T cells, which are key to immune responses, to peptides containing amino acids commonly found on meteorites: isovaline and α-aminoisobutyric acid.
The response was less efficient, with activation levels of 15% and 61% — compared to 82% and 91% when exposed to peptides made entirely of amino acids that are common on Earth.
“Life on Earth relies on essential 22 amino acids,” said study lead author Dr. Katja Schaefer, also from the Medical Research Council Centre for Medical Mycology at the University of Exeter and the Aberdeen Fungal Group in the Institute of Medical Sciences at the University of Aberdeen.
“We hypothesized that lifeforms that evolved in an environment of different amino acids might contain them in their structure.”
“We chemically synthetized ‘exo-peptides’ containing amino acids that are rare on Earth, and tested whether a mammal immune system could detect them.”
“Our investigation showed that these exo-peptides were still processed, and T cells were still activated, but these responses were less efficient than for ‘ordinary’ Earth peptides.”
Katja Schaefer et al. 2020. A Weakened Immune Response to Synthetic Exo-Peptides Predicts a Potential Biosecurity Risk in the Retrieval of Exo-Microorganisms. Microorganisms 8 (7): 1066; doi: 10.3390/microorganisms8071066
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