Reporter : Tang Yichen / Publisher : China Science News
Ref : http://news.sciencenet.cn/htmlnews/2020/8/444542.shtm
Translation, editing : Gan Yung Chyan, KUCINTA SETIA
Image : Early deletion of germinal centers and B-cells expressing Bcl-6 in lymph nodes of covid patients (Web Screenshot)
The massive release of a protein called cytokine may cause some of the most severe symptoms of covid. When a large number of immune cells release cytokines, inflammation is increased and a feedback loop is generated, so that more immune cells are activated, which is sometimes called a cytokine storm. A study published on August 19 in Cell, a journal of Cell Press, shows that some high levels of cytokines may also prevent infected persons from developing long-term immunity, because it is observed that patients only can produce very few B cells, and these cells are necessary for the formation of a lasting immune response.
"We have seen many studies showing that immunity to covid will not last, because antibodies will decline over time." Shiv Pillai, co-senior author of the paper, a professor at Harvard Medical School and a member of the Lagan Institute Said, "This study provides a mechanism to explain this low-quality immune response."
The researchers focused on the germinal center, the area where B cells (antibody-producing immune cells) differentiate in the lymph nodes and spleen. The differentiation and changes of antibody genes are necessary for the establishment of immunity against infectious pathogens.
"When we observed the lymph nodes and spleen of patients who died from covid, including some patients who died soon after getting the disease, we found that these germinal center structures have not yet formed." Professor of Pathology, Harvard Medical School and co-senior author Robert Padera said, "We decided to find out why."
Since covid is a new disease, when they started their research, there was no animal model used to study new coronavirus infection. Instead, the researchers gained some information from previous studies that involved mouse models of other infections that induce cytokine storm syndrome—a model of malaria and a model of bacterial infection that lost germinal centers.
In severe covid patients, the largest amount of cytokine released is called TNF. In infected mice, TNF appeared to prevent the formation of germinal centers. In the previous cytokine storm model, when mice were injected with antibodies to block TNF or delete the TNF gene, germinal centers were able to form. When researchers studied the lymph nodes of patients who died of this disease, they found high levels of TNF in these organs. This led them to conclude that TNF may also prevent covid patients from forming germinal centers.
"Some studies have shown that this lack of germinal centers will occur during SARS infection," Pillai said. "We even think that this phenomenon will occur in some Ebola patients, so it's not surprising."
The researchers also studied the blood and lymph tissues of infected people at different stages of covid. They found that even though germinal centers were not formed, B cells were still activated and appeared in the blood, which caused the patient to produce some neutralizing antibodies. "This is an immune response," Padera said. "It just doesn't come from the germinal center."
"Without germinal centers, antigens will have no long-term memory." Pillai added. He pointed out that research on other coronaviruses that can cause colds shows that a person may be infected with the same coronavirus three to four times in a year.
The authors said that despite these findings, they still believe that a successful SARS-CoV-2 vaccine can be developed without causing high levels of cytokine release.
Related paper information: http://dx.doi.org/10.1016/j.cell.2020.08.025
No comments:
Post a Comment