The emergence of adaptive immunity in response to the new Betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), occurs within the first 7 to 10 days of infection.
Understanding the key features and the B-cell evolution – and T-cell-mediated adaptive immunity to SARS-CoV-2 is essential to predict the outcomes of coronavirus disease 2019 (COVID-19) and to develop effective strategies to control the pandemic.
Determining the long-term immune memory of B and T cells against SARS-CoV-2 is also critical to understanding durable protection.A robust expansion of memory B cells and plasmablasts is detected early in infection, with secretion of serum IgM and IgA antibodies between day 5 and 7 and IgG between day 7 and 10 from the onset of symptoms.
In general, serum IgM and IgA titers decline after approximately 28 days (Figure) and IgG titers peak at approximately 49 days. Simultaneously, SARS-CoV-2 activates T cells in the first week of infection, and virus-specific CD4 + memory cells and CD8 + T cells supposedly peak within 2 weeks, but remain detectable at higher levels. lows for 100 or more days of observation.
Grifoni et al1 and others have identified SARS-CoV-2 specific memory CD4 + T cells in up to 100% and CD8 + T cells in approximately 70% of patients recovering from COVID-19.
Although severe COVID-19 is characterized by high viral titers, dysregulated innate inflammatory cytokines, and chemokine responses and prolonged lymphopenia, a dependent increase in antibodies or dominant CD4 + TH2-like cytokines (eg, IL-4, IL-5) , IL-13) do not appear to contribute to the acute severity of COVID-19.