I’ve mentioned previously that some people might be able to fight COVID-19 with T cells even if they don’t have antibodies to the virus. Over at Science, some information on a new study (emphasis mine):
It confirms that convalescent [i.e., recovering] patients from the current epidemic show T-cell responses. . . .
Turning to patients who had caught SARS back in 2003 and recovered . . . these patients still have (17 years later!) a robust T-cell response to the original SARS coronavirus’s N protein. . . . These cross-react with the new SARS CoV-2 N protein as well. This makes one think, as many have been wondering, that T-cell driven immunity is perhaps the way to reconcile the apparent paradox between (1) antibody responses that seem to be dropping week by week in convalescent patients but (2) few (if any) reliable reports of actual re-infection. That would be good news indeed.
And turning to patients who have never been exposed to either SARS or the latest SARS CoV-2, this new work confirms that there are people who nonetheless have T cells that are reactive to protein antigens from the new virus. As in the earlier paper, these cells have a different pattern of reactivity compared to people who have recovered from the current pandemic (which also serves to confirm that they truly have not been infected this time around). . . . It turns out that the T cells are recognizing particular protein regions that have low homology to those found in the “common cold” coronaviruses – but do have very high homology to various animal coronaviruses.
Very interesting indeed! That would argue that there has been past zoonotic coronavirus transmission in humans, unknown viruses that apparently did not lead to serious disease, which have provided some people with a level of T-cell based protection to the current pandemic. This could potentially help to resolve another gap in our knowledge, as mentioned in that recent post: when antibody surveys come back saying that (say) 95% of a given population does not appear to have been exposed to the current virus, does that mean that all 95% of them are vulnerable – or not?