This is a summary, written by members of the CITF Secretariat, of:

Gasser, R., Cloutier, M., Prévost, J., Fink, C., Ducas, É., Ding, S., Dussault, N., Landry, P., Tremblay, T., Laforce-Lavoie, A., Lewin, A., Beaudoin-Bussières, G., Laumaea, A., Medjahed, H., Larochelle, C., Richard, J., Dekaban, G.A., Dikeakos, J.D., Bazin, R., Finzi, A., Major role of IgM in the neutralizing activity of convalescent plasma against SARS-CoV-2, Cell Reports (2021), doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

Dr. Andrés Finzi, from the Université de Montréal, Dr. Renée Bazin from Héma-Québec, along with collaborators from Western University, are highlighting the importance of antibodies made early on in the infection in SARS-CoV-2 neutralization. This publication comes from their research funded in part by the Government of Canada through its COVID-19 Immunity Task Force (CITF) in collaboration with the Canadian Institutes of Health Research (CIHR).

It is widely recognized that the antibody or humoral response to SARS-CoV-2 is key to controlling infection and one of the ways that antibodies contribute to immunity is by its neutralizing capability. Neutralizing antibodies function by binding to the virus and blocking entry into host cells so that it is unable to infect and cause severe infection. There are different types of antibodies, immunoglobulins M (IgM), IgA, IgG, IgE, and IgD that function in various compartments of the body.

It was shown previously by Dr. Finzi, Dr. Bazin, and their respective teams at CRCHUM and Héma-Québec, that the neutralization capacity of SARS-CoV-2 declined after six weeks. To investigate the reason for this decline, they selectively removed each type of antibody from plasma of recovered COVID-19 patients to determine the impact on SARS-CoV-2 neutralization. Interestingly, the loss of neutralizing capacity was highest for IgM-depleted plasma with a 5.5-fold decrease, followed by IgG, and then IgA. This suggests that IgM plays an important role in the neutralization power of the plasma.

In summary, these results reveal the need to reassess antibody-based COVID-19 therapies, as some of the current ones could impair IgM production.