i came upon a terrific article today that can be found here;
https://tmblr.co/Z0_1woYYnLE0my00
It talks about the role of T cells in immunity and how they might impact natural resistance to SARS-CoV-2. Let me summarise some of the points made. First, T cells, what are they? There are two types of lymphocytes one rpduced in the Thymus, hence T-cell and one produced in the marrow, the B cell, the latter produce antibodies against a single virus. T cells come in several forms, Killer T cells kill virus-infected cells as well as cancer cells. They can also bring other immune cells scurrying to help. Here is a video of one in action against a cancer cell.
Other T cells are termed helper cells and they influence other cells and a further group are termed regulatory T cells and they allow tolerance to certain invading cells where they might cause an inappropriate immune reaction against our own cells. When these cells do not function effectively, we can develop autoimmune diseases such as rheumatoid arthritis and type one diabetes.
The author reports that several trials have shown that people can have T cells, that react to COVID 19 without having prior exposure, suggesting some of us may be naturally immune.
The evidence in part comes from testing blood taken several years before covid 19 appeared. It was found that these samples did not contain antibodies to COVID 19 but did contain T cells that reacted against COVID 19 (properly called SARS-CoV-2).
Three studies gave varying levels of this natural immunity ranging from 20-80%. It is thought this may result from exposure to another type of coronavirus causing the common cold.
This raises the possibility that the low levels of infection in the UK, as measured by antibody testing and swabs, is the result of widespread immunity to the virus. This might explain why levels of infection and deaths continue to fall in the face of a widespread easing of the lockdown, although the recent outbreak in Leicester is of concern.
In one study of seven families containing at least one infected individual, those infected produced antibodies and had a T cell response to the virus. Some of those family members exposed to the infected group developed mild symptoms but no antibodies yet six out of eight of these had a T cell response suggesting past SARS-CoV-2 infection. This provides further evidence that people can produce a T cell response without antibodies. Further, this raises the possibility of widespread immunity in the population.
Here is another interesting article suggesting the same thing;
https://news.ki.se/immunity-to-covid-19-is-probably-higher-than-tests-have-shown
In another case study of a cruise ship, of 217 passengers, 59% tested positive for COVID19, yet 81% of these had no symptoms, 18% had symptoms, 3% were intubated and one died. This again points to a possible natural immunity. It may be that the amount of virus you are exposed to, viral load, may also play a part in overcoming this natural immunity and explain the high levels of severe disease in members of the health care community. What has not been fully explained yet is why there are very significant differences between ethnic groups in the risk of serious illness and death following infection with SARS-CoV-2.
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