Although experts believe this possibility is unlikely, pre-existing T cells are very likely to increase the risk of severe Covid-19 symptoms. T cells that are ready to recognize the common cold coronavirus may only be slow to respond to the current coronavirus, and may waste the resources of other immune cell populations, which have an advantage in resisting new invaders. Dr. Ayer said: “Now, your immune system is distracted.”
T cells are also the coordinators of experts. Based on the signals they send, they can synchronize the cells and molecules of different parts of the immune system to mark group attacks, or quell these attacks to restore the body to its baseline. Dr. August said that if it turns out that cross-reactive T cells tend to calm the response, they can suppress a person’s immune defense and give it a chance to function.
It is not easy to separate it. Unlike antibodies to inanimate proteins that usually circulate in the blood, T cells are living cells, usually hollow in hard-to-reach tissues. Dr. Pepper said this makes them more difficult to extract, maintain and analyze.
Researchers can learn more by testing whether cross-reactive T cells are more abundant in patients with mild or severe Covid-19 cases, although such studies cannot prove cause and effect. Dr. Seth said that a more laborious task may involve measuring the level of cross-reactive T cells in a large number of healthy people and then waiting for them to be infected or sick due to the current coronavirus.
Strong evidence may also come from animal models, such as the rhesus monkeys that Dr. Iyer studied in her laboratory. Researchers can inject common coronaviruses into primates and observe how their immune response to the new coronavirus accumulates.
Dr. Pepper said that in less than a year since the pandemic broke out, many questions remain unanswered. Immunologists cannot fully predict how the human immune system will respond to this new virus. Even if science is developing fastest, interaction must be studied in real time.
Dr. Pepper said this is a frustrating reality: “We don’t know it until we see it in real life.”