A new study conducted on monkeys has shown that T cells are not crucial for immune memory for SARS-CoV-2 or recovery from acute COVID-19 infection. In primates, even with very weak cellular immunity, antibodies provided a good level of protection against re-infection. The results of the study are published in the journal of the American Society of Microbiologists mBio.
To test how important natural T-cell immunity is for protection against coronavirus, American scientists led by Kim Hasenkrug from the National Institute of Allergy and Infectious Diseases took model rhesus macaques and using standard reagents weakened their production of CD4+ and CD8+T-lymphocytes.
CD8+ cells directly attack and kill infected cells, and CD4+ triggers an immune response by recognizing pathogens and secreting cytokines — small proteins that signal the need for other immune cells to act, including CD8+ and antibody-producing B cells.
For six weeks after the macaques were infected, the researchers took swabs from their nose and pharynx and performed bronchoscopy to measure the level of the virus in the nose, mouth, and lungs, as well as swabs from the rectum to determine whether the virus is excreted from the intestines. Six weeks later, the researchers retested the monkeys for SARS-CoV-2 and performed a blood test, which allowed us to assess the response of immune memory.
The results showed that the severity of CAVID-19 disease did not depend on the state of T-cells, and macaques with severe depletion of T-lymphocytes developed the same powerful immune memory reactions to the second infection. The monkeys ‘ body has created a good immune memory response against the coronavirus and in the case of depleted T cells.
“We found that we have really good memory responses regardless of whether we depleted the T cells or not. Basically, we found very strong virus-neutralizing antibodies — the most important agents in the fight against infection. This was unexpected for most immunologists, virologists, and vaccine developers,” Kim Hasenkrug said in a press release from the American Society of Microbiologists.
“If there is a memory response, you will get a much faster immune response and control over the virus. This is how vaccinations work. Once your body detects a viral pathogen, the next time it sees it, you will be able to get a much faster and stronger immune response. Now we know that the most important antibodies for protection against coronavirus are the antibodies associated with vaccination and not the T-cell response,” the scientist continues.
Another interesting effect that the authors of the study observed was the switching of T-cell classes, which occurred as they were depleted. For example, when CD8+ cells were depleted, CD4+ cells, or B-cells, became stronger. In some animals with a decrease in the functions of T-lymphocytes, the antibody immune response became stronger.
“We don’t have a solid explanation of why this happened, but we think it’s due to some kind of compensatory reaction. When animals lack something, they try to make up for it by producing more of something else,” Hasenkrug explains. The authors hope that their results will play an important role in the development of new-generation vaccines and medicines.