Immune cell landscape in symptomatic and asymptomatic SARS-CoV-2 infected adults and children in urban Dhaka, Bangladesh

OBJECTIVES: The study of cellular immunity to SARS-CoV-2 is crucial for evaluating the course of the COVID-19 disease and for improving vaccine development. We aimed to assess the phenotypic landscape of circulating lymphocytes and mononuclear cells in adults and children who were seropositive to SARS-CoV-2 in the past 6 months. METHODS: Blood samples (n = 350) were collected in a cross-sectional study in Dhaka, Bangladesh (Oct 2020-Feb 2021). Plasma antibody responses to SARS-CoV-2 were determined by an electrochemiluminescence immunoassay while lymphocyte and monocyte responses were assessed using flow cytometry including dimensionality reduction and clustering algorithms. RESULTS: SARS-CoV-2 seropositivity was observed in 52% of adults (18–65 years) and 56% of children (10–17 years). Seropositivity was associated with reduced CD3(+)T cells in both adults (beta(β) = −2.86; 95% Confidence Interval (CI) = −5.98, 0.27) and children (β = −8.78; 95% CI = −13.8, −3.78). The frequencies of T helper effector (CD4(+)T(EFF)) and effector memory cells (CD4(+)T(EM)) were increased in seropositive compared to seronegative children. In adults, seropositivity was associated with an elevated proportion of cytotoxic T central memory cells (CD8(+)T(CM)). Overall, diverse manifestations of immune cell dysregulations were more prominent in seropositive children compared to adults, who previously had COVID-like symptoms. These changes involved reduced frequencies of CD4(+)T(EFF) cells and CD163(+)CD64(+) classical monocytes, but increased levels of intermediate or non-classical monocytes, as well as CD8(+)T(EM) cells in symptomatic children. CONCLUSION: Seropositive individuals in convalescence showed increased central and effector memory T cell phenotypes and pro-resolving/healing monocyte phenotypes compared to seronegative subjects. However, seropositive children with a previous history of COVID-like symptoms, displayed an ongoing innate inflammatory trait.