Cytokine storm may be keeping COVID-19 patients from developing long-term immunity: Study

Cytokine storm is an inflammatory condition associated with COVID-19 infection that occurs when a person’s body releases too many pro-inflammatory cytokines. If left untreated, it can cause organ damage and increase the risk of death. In a recent study, a team of researchers led by Dr Shiv Pillai, an investigator at Ragon Institute of Massachusetts General Hospital, MIT and Harvard and a professor at the Harvard Medical School, claimed that cytokine storms may be the reason why COVID-19 patients are not able to develop lasting immunity against the SARS-CoV-2 virus. The findings of the study published in the peer-reviewed journal Cell suggest that this is due to the absence of germinal centers in the spleen and lymph nodes of coronavirus patients. Germinal centers are specific areas in spleen and lymph nodes where B cells (the cells that release antibodies) turn into memory cells. It is the memory cells that determine long-lasting immunity against a pathogen. Lymphoid organs, germinal centers and B and T cells The human immune system contains a network of specialised tissues and organs which produce and develop specific B and T cells in the body. Bone marrow and thymus produce B and T cells and are hence called primary lymphoid organs. The spleen, lymph nodes and Peyer’s patches are called secondary lymphoid organs as they expose these cells to antigens. B and T cells are lymphocytes (type of white blood cell) that help fight infections. These cells are a part of the acquired immunity:  the immunity we develop after exposure to pathogens as opposed to the innate immunity, which we are all born with. Germinal centers develop in secondary lymphoid organs when a pathogen enters the body. Antigen-specific B cells are chosen and proliferate inside these areas. There are two types of B cells: plasma cells and memory B cells. The former release antibodies and the latter mainly work on remembering an antigen so that a quick immune response is generated the next time the same antigen enters the body. T cells, especially the T follicular helper cells, help stimulate B cell proliferation within germinal centers and help in the production of antibody diversity. Effect on germinal centers in COVID-19 patients For the latest study, researchers looked into the spleens and lymph nodes of patients who died of COVID-19. Some of these patients had died within 10 days of hospitalisation while others had died within 15 to 36 days. However, all of these patients had one thing in common: the absence of germinal centers. These patients also showed a marked reduction in B cells. Without B cells, there won’t be a high-quality immune response to produce long-lasting antibodies. Interestingly, T follicular helper cells were diminished in these patients, which Dr Pillai suggested as the possible reason for the reduction in B cells. Link with cytokine storm Animal studies have previously shown that cytokines, especially TNF can prevent the formation of T follicular helper cells. Those with severe COVID-19 were found to have large amounts of TNF in their germinal centers. T follicular cells are also differentiated (become specific to an antigen) inside the lymphoid organs before they go on to stimulate B cells. Explaining the study, Dr Pillai said in a news release, “Without the formation of germinal centers, there is unlikely to be long-term memory to this virus developing from natural infections, meaning that while antibodies may protect people for a relatively short time, a single person who recovers from the disease could get infected again, perhaps six months later, or even multiple times with SARS-CoV-2. This suggests that developing herd immunity may be difficult.” For more information on cytokine storm, read our article on Cytokine storm: symptoms, causes, complications Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.