Differential decline of SARS‐CoV‐2‐specific antibody levels, innate and adaptive immune cells, and shift of Th1/inflammatory to Th2 serum cytokine levels long after first COVID‐19

Background SARS‐CoV‐2 has triggered a pandemic and contributes to long‐lasting morbidity. Several studies have investigated immediate cellular and humoral immune responses during acute infection. However, little is known about long‐term effects of COVID‐19 on the immune system. Methods We performed a longitudinal investigation of cellular and humoral immune parameters in 106 non‐vaccinated subjects ten weeks (10 w) and ten months (10 m) after their first SARS‐CoV‐2 infection. Peripheral blood immune cells were analyzed by multiparametric flow cytometry, serum cytokines were examined by multiplex technology. Antibodies specific for the Spike protein (S), the receptor‐binding domain (RBD) and the nucleocapsid protein (NC) were determined. All parameters measured 10 w and 10 m after infection were compared with those of a matched, noninfected control group (n = 98). Results Whole blood flow cytometric analyses revealed that 10 m after COVID‐19, convalescent patients compared to controls had reduced absolute granulocyte, monocyte, and lymphocyte counts, involving T, B, and NK cells, in particular CD3+CD45RA+CD62L+CD31+ recent thymic emigrant T cells and non‐class‐switched CD19+IgD+CD27+ memory B cells. Cellular changes were associated with a reversal from Th1‐ to Th2‐dominated serum cytokine patterns. Strong declines of NC‐ and S‐specific antibody levels were associated with younger age (by 10.3 years, p