Neutralizing Antibodies in SARS-CoV-2 Infected Children

The adaptive immune system, or acquired immunity, is a strategic immune response mounted by specific antibodies. This response uses immunological memory to enhance the immune response and is activated by exposure to pathogens. Although it tends to be slower than the innate response, it is an important step in the process of eliminating pathogens.

With the currently ongoing COVID-19 pandemic, more knowledge on the adaptive immunity in children in relation to the SARS-CoV-2 virus is paramount in defining possible immunization strategies and in reconsidering control measures during the pandemic.

A recent study conducted by investigators in Italy analyzed anti-SARS-CoV-2 antibodies as well as their neutralizing activity, alongside antigen specific cellular response, in relation to viral loads in nasopharyngeal swabs. The data was presented during the Conference on Retroviruses and Opportunistic Infections (CROI) 2021 virtual sessions.

The study included 42 participants whose viral loads were measured by RT-PCR and digital droplet PCR tests on longitudinal samples of nasopharyngeal swabs at 7 days after symptom onset. A focus forming assay was used to test virus infectivity and virus antibodies were investigated by Diasorin and neutralization assays.

Additionally, SARS-CoV-2 specific CD4, CD40L+ T-cells and Spike specific B-cells were analyzed by flow cytometry. 2 Olink panels were used to measure plasma proteomic profiling. The Mann-Whitney, a test used to compare differences between two independent groups, was used to compare means in individuals with neutralizing activity or not.

Findings from the study showed that higher levels of viral load were found in seronegative patients expressed in terms of both SARS-CoV-2 antibodies and neutralizing activity. Lower virus infectivity was also associated with higher SARS-CoV-2 antibodies and neutralizing activity.

The development of humoral response was associated with the presence of SARS-CoV-2 specific IgD-CD27+ B cells, with a higher frequency of SARS-CoV-2 specific B cells found in seropositive compared to seronegative.

“This work provides a virological and immunological characterization of SARS-CoV-2 infected children presenting a differential Ab-mediated neutralizing activity,” the authors wrote. “It demonstrates that children with neutralizing antibodies present reduced viral load, faster virus clearance and lower in vitro infectivity. These data provide information that can drive vaccination endpoints and quarantine measures policies.”