Middle-cell immunity may be more important than neutralizing antibodies in COVID-19 production

An interesting new study sheds light on some important differences between asymptomatic and symptomatic patients with coronavirus disease 2019 (COVID-19). The introduction, which appeared on the medRxiv * preprint server in December 2020, adding important details to the coronavirus syndrome 2 (SARS-CoV-2) infectious disease study.

Study details

The study included 193 patients with SARS-CoV-2 infection in two Chinese cities, from January 21 to March 6, 2020. They included 31 asymptomatic carriers, 14 presymptomatic patients, and 149 patients. symbolic.

The study included four family groups, including 15 subjects. Of these, 3 were children aged 12 or under, 3 were adults aged between 18 and 60, and one was a 75-year-old woman.

Among the 8 symbolic cases, 4 were older than 60 years, and had severe disease. Of those patients who were very ill, three had comorbidities. The other 4 had moderate illness, and were between 18 and 60 years old, and only 1 had other harmful illnesses.

Poor antibody response in asymptomatic patients

The researchers found that asymptomatic infections occurred in younger patients, who had higher white cell and lymphocyte counts, lower C-reactive protein levels, and lower viral loads. They would also clear the virus faster, as evidenced by a faster cessation of viral shedding. More patients who acquired the disease from house contacts had more asymptomatic infections compared to typical patients, at about 90% vs. about 60%, respectively.

After seroconversion occurred, IgM-positive became IgM-negative more rapidly in asymptomatic carriers, compared with COVID-19 patients (7.5 days and 25.5 days, respectively). IgG seroconversion occurred at the same rate in both groups. However, IgG positase persisted in two-thirds of asymptomatic carriers compared with one-third of COVID-19 model patients.

In typical patients, viral loads were higher compared with presymptomatic patients. The latter also shed virus longer than asymptomatic individuals. Thus, asymptomatic carriers appear to show evidence of higher antiviral immunity leading to faster clearance of the virus, compared to typical patients. This immunity does not appear to be due to mediated antibody responses, since both IgM and IgG showed faster decay levels in asymptomatic carriers than in COVID-19 patients.

Effective immune response mainly cellular

These data indicate that low immunity against SARS-CoV-2 was not effectively aroused by brief exposure to SARS-CoV-2 in asymptomatic carriers or in those with stronger tissue and cellular immunity. . ”

Instead, “primary hereditary and central-cell immunity should play key roles in viral replication in asymptomatic carriers,” as identified by the viral carriers. lowest and shortest duration of viral peeling in asymptomatic patients. Higher viral load is an indication of a higher risk of COVID-19 side effects.

In an earlier study, the authors showed that progressive COVID-19 infection occurs in patients with lower T cell count in the blood, fewer CD4 + T cells and CD8 + T cells. else, the proportion of circulating neutrophils is higher in these patients, with a higher ratio of neutrophils to lymphocytes. Inflammatory markers such as IL-6 (interleukin-6), C-reactive protein (CRP), and procalcitonin are also elevated.

Effect T cell disruption is thought to be fundamental in the development of acute or chronic COVID-19. This is supported by other studies showing low levels of natural killer (NK) cells, and CD4 +, CD8 + and CD3 + T cells. In the recovery period, however, there is a large and rapid expansion. of cytotoxic effector T cells belonging to CD4 + effector-granulysin, CD8 + effector-granulysin, and NKT CD160 cells. Both intracellular and T cell immunity is thus attenuated in advanced COVID-19, which may be due to high levels of systemic inflammation. The rate of systemic inflammation in asymptomatic carriers is also lower.

What is the impact?

Approximately 3 in 4 patients with SARS-CoV-2 infection, asymptomatic or otherwise, did not develop IgG in the incubation period or thereafter. The role of humoral immunity is therefore questioned. The fact that IgG seroconversion from positive to negative, or weakly positive, only about 30% in a 160-day period from diagnosis, indicates that anti-SARS-CoV-2 IgG levels are declining significantly after disease. While this occurred in more than half of asymptomatic patients, it was seen in a quarter of symptomatic patients. This finding has been reported in front-line health workers in the U.S. and France.

These findings highlight the importance of cell-specific immunity to SARS-CoV-2 rather than neutralization of antibodies. The effectiveness of a vaccine should therefore be evaluated in terms of the ability of the vaccine to stimulate cellular immunity.

* Important message

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical / behavioral practice, or treatment as established information.