In a letter to the Editor in Nature Medicine , Australian scientists report immune response kinetics in a 47-year old patient with mild-to-moderate coronavirus (COVID-19) disease, who required hospitalisation but not ventilation.
Increased antibody-secreting cells (ASCs), follicular helper T cells (TFH cells), activated CD4+ T cells, CD8+ T cells, and immunoglobulin M (IgM) and IgG antibodies that bound to the COVID-19 virus, were detected in blood before symptomatic recovery. This immunological response persisted for seven days following full resolution of symptoms.
- ASCs appeared and peaked on Day 8.
- Circulating TFH occurred on Day 7, increasing at Day 8/9.
- Both ASCs and circulating TFH cells were prominently present during convalescence.
- Co-expression of CD38 and HLA-DR is a key phenotype of CD8+ viral response, which rapidly increased from Day 7 to Day 8/9, decreasing at Day 20.
- Co-expression of CD38 and HLA-DR on CD4+ T cells also increased between Day 7 and Day 9.
- Rapid increases in activated CD38+HLA-DR+ T cells preceded the resolution of symptoms.
- Minimal pro-inflammatory cytokines, predictive of severe clinical outcomes for influenza, were present even while symptomatic.
Immune parameters should be characterised in larger cohorts of people with COVID-19 with different disease severities to predict disease outcome, evaluate new interventions, and inform on protective vaccine candidates.