The Immune System’s Fight against COVID-19

By Sahana Shankar, Ph.D. Candidate

In the past month, COVID-19 has taken over the news cycle across science, health, economics, geopolitics, drug discovery, epidemiology, and many more segments. With a barrage of information available on cases reported, quarantine measures, clinical trials for drugs and vaccines, one area that is slightly under-reported is the physiological manifestation of the SARS-CoV-2 virus and the relevant immunes responses in the human body. In broad strokes, it causes flu-like symptoms and in severe cases, it attacks the respiratory system causing pneumonia and breathing difficulties.

A New Study

Researchers at the Doherty Institute for Infection and Immunity, a joint venture between the University of Melbourne and The Royal Melbourne Hospital, Australia have conducted a study underlining the “kinetics of immune responses”, “clinical and virological features” of a hospitalized COVID-19 patient with mild-to-moderate infection who was able to recover without antiviral and steroid therapy, suggesting that our immune system has the potential to fight the SARS-CoV-2 virus.

The study focused on a woman in her late 40s who traveled from Wuhan, China to Melbourne, Australia. She had no other pre-existing medical conditions and developed flu symptoms 11 days after arrival in Melbourne. She did not have any physical contact with known COVID-19 patients or the Hunan seafood market. Her symptoms included elevated body temperature (38.5°C) and bi-lateral rhonchi (low-pitched rattling sounds from the lungs due to possible obstructions or secretions in the airways). SARS-CoV-2 virus was detected by RT-PCR from nasal swabs, sputum, and fecal samples. She was treated with intravenous fluid rehydration and did not require supplemental oxygen. After 10 days of hospitalization, her symptoms were resolved and was advised home isolation.

 

Immune Responses against COVID-19

During her hospitalization, the doctors surveyed the breadth of her immune response to COVID-19 at four different time points by analyzing blood samples based on information available from other influenza cases. One of the key players of viral immunity and recovery is the proliferation of specific types of immune cells that produce antibodies to ward off the viral attack. As expected, the population of antibody-secreting cells (ASCs), follicular T-helper cells (TFHs ) peaked and were higher in the patient compared to healthy controls. The higher levels of ASCs and TFHs were observed from the time of viral clearance (day 7) to convalescence (day 20), suggesting that the body recruits these immune responses to clear the virus.

Further investigations into the types of T cells that drive this viral immunity pointed to activated CD38+HLA-DR+ T cells, especially CD8+ T cells that produce IgM and IgG antibodies against the SARS-CoV-2 virus. Another interesting finding from the study was that the patient had a single nucleotide polymorphism (SNP) rs12252-C/C in the gene IFITM3, which is linked to severe influenza. According to the 1000Genomes project, the IFITM3-rs12252-C/C SNP is prevalent in 26.5% of the Chinese population, suggesting that this SNP could be a predictive indicator of COVID-19 in larger populations to screen and diagnose further cases.

The study was made possible by the Sentinel Travelers and Research Preparedness for Emerging Infectious Disease (SETREP-ID) initiative and was led by the Royal Melbourne Hospital Infectious Diseases physician Irani Thevarajan, MD. SETREP-ID is a platform that facilitates a broad range of biological sampling from travelers returning to Australia in the event of a new and unexpected infectious disease outbreak. “When COVID-19 emerged, we already had ethics and protocols in place so we could rapidly start looking at the virus and immune system in great detail,” Dr. Thevarajan said. She hopes to continue to work on elucidating the physiological and immune response in COVID-19 fatalities which will be instrumental in building a database to assist with rapid response to emerging viruses in the future.

These results published in the journal Nature Medicine on 16 March 2020, provides insights into mild and symptomatic COVID-19 and the immune response it elicits in an otherwise healthy individual. This news gives hope at a time when countries are burdened with managing the COVID-19 pandemic. It is the first of many studies that can help characterize immune parameters to be checked in patients to improve prognostic and recovery rates. Since up to 80% of reported COVID-19 cases are mild to moderate, this understanding of the human body’s ability to tackle the virus is of importance to clinicians to prescribe appropriate therapeutic approaches.

Editor: Rajaneesh K. Gopinath, Ph.D.

Related Article: Experimental Plasma Treatment for COVID-19 Gets FDA Support

References
  1. https://www.nature.com/articles/s41591-020-0819-2
  2. https://about.unimelb.edu.au/newsroom/news/2020/march/covid-19-the-immune-system-can-fight-back

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