By Jessica Dickens
A recent study by the Karolinska Institute in Sweden suggests antibody testing for immunity to Coronavirus could show an underestimation of immunity, as T-cells also play a vital role in providing immunity: “Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in”, says one writer of the research paper.
COVID-19 antibody testing is often used to determine whether an individual has previously been infected by the virus. Testing can be used to interpret the virus spread in a particular area and may be the main way officials implicate a local lockdown in the future.
However, Government guidance explains that these antibody tests are not perfect. A positive test does not necessarily always show whether someone is immune to Coronavirus and unable to infect others.
Additionally, the Government guidance explained that a negative test can show that the laboratory findings do not indicate any antibodies to the virus, which suggests that the person has not been exposed to COVID-19. A negative test could also imply that antibodies have not been retained from prior infection, or that the test was conducted before the body’s antibody response.
Antibodies are made by the body in a shape that is specific to markers on the virus, called antigens. The binding of antibodies to the antigens can stop pathogens, such as COVD-19, entering host cells. These can provide a signal of the pathogen’s location to cells of the immune system, including phagocytic cells, which play a role in engulfing foreign particles in an attempt to protect the body.
Another example of this is T cells which are involved in the immune response to infection. They activate other immune cells and directly attack infected host cells, by stopping the infected cells from spreading to healthy cells.
An experiment conducted on 200 people, carried out by researchers at the Karolinska Institute in Sweden, tested for antibodies and T cells. T cell immunity was found in individuals with confirmed COVID-19 symptoms and was also found in many asymptomatic participants, also infected by the virus. These asymptomatic individuals were likely to have had COVID-19 exposure but may have tested negative for the antibody test.
Furthermore, “Roughly 30 percent of the blood donors who’d given blood in May 2020 had COVID-19-specific T cells, a figure that’s much higher than previous antibody tests have shown,” stated consultant Soo Aleman, who, along with her colleagues, have been testing these patients and their families at Karolinska University Hospital.
Results also showed that patients severely affected with COVID-19 produced a high antibody and T cell response. Patients with milder symptoms did not always have a detectable antibody response but did have a distinguishable T cell response.
The evidence found in these tests suggests more widespread immunity than determined by antibody tests. As Professor Danny Altmann at Imperial College London describes, this study gives evidence that “antibody testing alone underestimates immunity”.
However, Marcus Buggert, an assistant professor and one of the authors of the Karolinska Institute study explains, it is still unclear whether the presence of specific T cells completely prevent infection. It is possible that the T cells only protect the individual, whilst allowing transmission of the virus to others. As individuals with these specific T cells may still be able to spread the virus, this may not promote herd immunity.
Currently, mass T-cell testing to determine COVID-19 immunity is an unlikely prospect due to the complexity and the increase in difficulty to identify T cells compared to that of detecting antibodies.
More research is needed, using larger research groups, but the Karolinska Institute study does question the immunity figures currently circulating in our news.
It is well recognised that T cells play a very important role in our immune system to eliminate pathogens and through this research, it is hoped that we can further understand their impact on COVID-19 patients and future protection.