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The immune system provides a long-lasting defence after recovery from COVID-19

Research shows that those recovering from COVID-19 continued to improve their antibodies months after initial infection, potentially due to exposure to remnants of the virus hidden in the gut.

These recent findings provide the strongest evidence yet that the immune system "remembers" the virus and, remarkably, continues to improve the quality of antibodies even after the infection has waned. Antibodies produced months after the infection showed increased ability to block SARS-CoV-2, as well as its mutated versions such as the South African variant.

Researchers found that these improved antibodies are produced by immune cells that have kept evolving, apparently due to continued exposure to the remnants of the virus hidden in the gut tissue.

Based on these findings, researchers suspect that when the recovered patient next encounters the virus, the response would be both faster and more effective, preventing re-infection.

Antibodies, which the body creates in response to infection, linger in the blood plasma for several weeks or months, but their levels significantly drop with time. The immune system has a more efficient way of dealing with pathogens: instead of producing antibodies all the time, it creates memory B cells that recognize the pathogen, and can quickly unleash a new round of antibodies when they encounter it a second time.

But how well this memory works depends on the pathogen. To understand the case with SARS-CoV-2, researchers studied the antibody responses of 87 individuals at two-time points: one month after infection, and then again six months later. As expected, they found that although antibodies were still detectable by the six-month point, their numbers had markedly decreased. Lab experiments showed that the ability of the participants' plasma samples to neutralize the virus was reduced by five-fold.

In contrast, the patients' memory B cells, specifically those that produce antibodies against SARS-CoV-2, did not decline in number and even slightly increased in some cases.

A closer look at the memory B cells revealed that these cells had gone through numerous rounds of mutation even after the infection resolved, and as a result, the antibodies they produced were much more effective than the originals. Subsequent lab experiments showed this new set of antibodies were better able to latch on tightly to the virus and could recognize even mutated versions of it.


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