Patients with severe COVID-19 develop antibodies faster than those with mild cases of the disease, according to Israeli scientists. The antibody targeting the viral protein that binds the virus to human cells develops at a relatively early stage of the disease. This means that the test developed by the researchers may potentially serve as a diagnostic tool, and as a means for fast and effective population surveys.

A team of researchers were led by Prof. Motti Gerlic and Prof. Ariel Munitz of the microbiology and clinical immunology department at Tel Aviv University’s Sackler School of Medicine and the Sharon Hospital of the Rabin Medical Center in Petah Tikva.

While patients with severe coronavirus disease developed antibodies faster than those with a mild case, in the long run, the level of antibodies was similar in all patients. Levels of the antibody targeting the viral protein that binds the virus to human cells remained high in the patients’ blood for the first two months following contagion – possibly indicating immunological memory. The serological test developed at the university will soon be sent to Israel’s Health Ministry for validation so that it may be used in surveys of the general population.

The team applied an innovative antibody test to some 70 COVID-19 patients at the Sharon Hospital. Examining the development of antibodies targeting two different viral proteins in the patients’ bodies, they found that severely ill patients developed the antibodies at a faster rate than those with a mild case of the disease. In addition, antibodies of the type IgG were maintained in the blood of most patients throughout the study. This project has important implications for our understanding of the immune response to SARS-CoV-2, as well as future tracking of the effectiveness of vaccines and population surveys (serological tests). 

The antibody targeting the viral protein that binds to human cells develops at a relatively early stage of the disease. This means that the test may serve as a diagnostic tool, and as a means for fast and effective population surveys.

“Our first finding,” said Munitz, was that not all viral proteins generate a rapid immune response], but that antibodies targeting the RBD [recombinant receptor-binding domain] protein did develop very quickly once the symptoms appeared. This finding is quite significant, because it suggests that the test we used may be utilized as a diagnostic tool at different stages of the illness.”

Patients with mild, moderate and severe COVID-19 all developed the same level of antibodies, he continued. “This is important, because one might have thought that the severely ill became so sick because they did not develop a sufficient amount of antibodies and were thus unable to combat the virus effectively. We assume that the fast development of antibodies in these patients indicates that their immune system is hyper-active, but this hypothesis requires further research.”

Levels of the antibody targeting the viral protein that binds the virus to human cells remained high in the patients’ blood for the first two months following contagion – possibly indicating immunological memory.

“We measured the levels of antibodies in the patients’ blood when they arrived at the hospital, during the period of hospitalization and after their release,” noted Gerlic. 

“We tried to understand whether the level of antibodies in their blood corresponded in any way to the severity of the illness, whether the antibodies developed in a similar way in all patients, and whether they remained in the blood for long periods of time – a critical factor for the ‘herd immunity’ we all wish to attain. We found that at later stages of the disease, about 50 days after the initial appearance of symptoms, a significant decline occurred in the presence of antibodies types IgM and IgA, regardless of the severity of the illness,” he added.

In the new study, the team used a new serological test developed in their lab. The Israel Defense Forces (IDF) Medical Corps has already used the serological test developed by Gerlic and Munitz to detect COVID-19 antibodies in the blood of soldiers.