A research study cautiously suggests that previous exposure to common cold viruses could play a role in the varied immune responses observed in patients infected with the SARS-CoV-2 virus.
Previous research by the same group showed that people unexposed to the SARS-CoV-2 virus also carried memory helper T cells, a kind of immune cell, which reacted to the SARS-CoV-2 virus. This puzzling result led the research team to study if these T cells were the result of previous exposure to common cold coronaviruses. The new study was published in the recent issue of Science journal.
The study was carried out with samples collected during the period between March 2015 to March 2018 and from participants who had no exposure to the SARS-CoV-2 virus. They then selected the immune cells from these participants that reacted to the SARS-CoV-2 virus. Using these cross-reactive immune cells, the scientists identified parts of the SARS-CoV-2 virus that were recognized by the immune cells. They also compared these virus fragments with fragments from four types of common cold-causing coronaviruses.
Using a technique to detect activated T cells, the team showed that the reactive T cells that recognize SARS-CoV-2 virus fragments actually cross-react with corresponding fragments from common cold viruses. This is direct evidence showing that some groups of people carry memory immune cells that are produced in response to a prior common cold virus infection that also reacts with the SARS-CoV-2 virus. As Dr. Daniela Weiskopf, co-lead on the study, explains, “We have now proven that, in some people, pre-existing T cell memory against common cold coronaviruses can cross-recognize SARS-CoV-2, down to the exact molecular structures.”
The presence of the memory immune cells could prime the immune system to better recognize and fight the SARS-CoV-2 virus. As Dr. Sette, co-lead on the study explains, “Immune reactivity may translate to different degrees of protection. Having a strong T cell response, or a better T cell response may give you the opportunity to mount a much quicker and stronger response.” It could explain why some people have milder COVID-19 symptoms compared to others. However, the researchers emphasize that drawing any conclusions regarding pre-existing immune cells against common cold viruses and the severity of COVID-19 infection is premature and highly speculative.
This study has shown that the spike protein, which has been the focus of a lot of research, is not the only part of the SARS-CoV-2 virus that can react with the immune cells. Other parts of the virus also elicit a response from the T cells. It also highlights that in addition to the antibody-producing B cells, T cells are also key to fighting the SARS-CoV-2 virus. However, it is not yet possible to conclude that a previous common cold infection can protect against SARS-CoV-2.
Written by Bhavana Achary, PhD
Original study: Mateus J, Grifoni A, Tarke A, et al. Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans [published online ahead of print, 2020 Aug 4]. Science. 2020
Press release: https://www.eurekalert.org/pub_releases/2020-08/ljif-etc080320.php
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