Why some Covid-19 cases turn severe while others don't

A recent study suggests that the virus behind Covid-19 has the potential to turn important immune cells into ones that weaken the body's ability to fight the infection.While finding out what makes some people develop severe Covid-19, researchers from Johns Hopkins University have found that the SARS-CoV-2 virus may alter neutrophils, the most common type of white blood cells, in a way that weakens the immune response.advertisementThe study, funded by the US National Institutes of Health and published in Science Translational Medicine, reveals that neutrophils in Covid-19 patients may lose their ability to fight infections.
Instead, these cells begin suppressing other immune cells, particularly T cells, which are essential for clearing viruses from the body.'In some Covid infections, the virus appears to reprogram neutrophils into a different type of cell that suppresses T cells. This may help explain why some people develop severe illness,' said Dr Andrea Cox, senior author of the study.These altered cells are known as PMN-MDSCs (polymorphonuclear myeloid-derived suppressor cells), which have been seen in cancer and other non-viral diseases but not commonly in viral infections like Covid-19.The researchers analysed blood samples from 39 hospitalised Covid-19 patients and compared them with samples from nine healthy individuals. None of the patients had received Covid vaccines or immunosuppressant drugs like dexamethasone. advertisementIn those with severe Covid-19, the team found that neutrophils had changed form, they had 'degranulated,' releasing their contents and morphing into PMN-MDSCs. These reprogrammed cells expressed two proteins, LOX-1 and PD-L1, known to suppress T cell activity.When the researchers exposed healthy neutrophils to the virus in the lab, they observed the same transformation: the cells began suppressing T cells, stopping them from multiplying and releasing cytokines, signalling proteins that activate other immune responses.Interestingly, when the same experiment was done using the H1N1 influenza virus, the neutrophils did not convert into suppressor cells, indicating a unique feature of SARS-CoV-2.There may already be a treatment that could counter this effect. The researchers added PD-L1-blocking antibodies, a type of drug used in cancer therapy, to neutrophils exposed to SARS-CoV-2. The result: T cells were less suppressed and became more active."This suggests that combining PD-L1 antibodies with antiviral drugs, or even using them alone when antivirals aren't possible, might help patients with severe Covid,' Cox said.The CDC defines severe Covid-19 as illness that results in hospitalisation, ICU admission, or death.This study offers a deeper understanding of how SARS-CoV-2 might hijack the immune system and lead to severe illness and opens new doors for treatments that could help the body fight back more effectively.Must Watch

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