Immunological imprint of COVID-19 on human peripheral blood leukocyte populations

Abstract

Background: SARS-CoV-2 has triggered a pandemic that is now claiming many lives. Several studies have investigated cellular immune responses in COVID-19-infected patients during disease but little is known regarding a possible protracted impact of COVID-19 on the adaptive and innate immune system in COVID-19 convalescent patients.

Methods: We used multiparametric flow cytometry to analyze whole peripheral blood samples and determined SARS-CoV-2-specific antibody levels against the S-protein, its RBD-subunit, and viral nucleocapsid in a cohort of COVID-19 convalescent patients who had mild disease ~10 weeks after infection (n = 109) and healthy control subjects (n = 98). Furthermore, we correlated immunological changes with clinical and demographic parameters.

Results: Even ten weeks after disease COVID-19 convalescent patients had fewer neutrophils, while their cytotoxic CD8⁺ T cells were activated, reflected as higher HLA-DR and CD38 expression. Multiparametric regression analyses showed that in COVID-19-infected patients both CD3⁺ CD4⁺ and CD3⁺ CD8⁺ effector memory cells were higher, while CD25⁺ Foxp3⁺ T regulatory cells were lower. In addition, both transitional B cell and plasmablast levels were significantly elevated in COVID-19-infected patients. Fever (duration, level) correlated with numbers of central memory CD4⁺ T cells and anti-S and anti-RBD, but not anti-NC antibody levels. Moreover, a "young immunological age" as determined by numbers of CD3⁺ CD45RA⁺ CD62L⁺ CD31⁺ recent thymic emigrants was associated with a loss of sense of taste and/or smell.

Conclusion: Acute SARS-CoV-2 infection leaves protracted beneficial (ie, activation of T cells) and potentially harmful (ie, reduction of neutrophils) imprints in the cellular immune system in addition to induction of specific antibody responses.

Keywords: B cells; SARS-CoV-2; T cells; clinical immunology; coronavirus disease 2019; flow cytometry; infections; lymphocytes.

Figure 1

Impact of primary SARS‐CoV‐2 infection on absolute counts of leukocyte subpopulations as determined 10 weeks after disease onset. Shown are absolute values of the indicated leukocyte populations in peripheral blood of healthy control subjects (HC) and COVID‐19 convalescent patients (COVID‐19). Bars show mean values, whiskers the standard deviation, and open circles the values of single individuals. Data show pooled results of daily stainings (whole blood, 5‐9 individuals per day) of n = 98 for HC, and n = 109 for COVID‐19 convalescent patients, except for panels determining HLA‐DR expression where n = 97 for HC. P‐values were determined by Mann‐Whitney U‐test and are indicated

Figure 2

Impact of primary SARS‐CoV‐2 infection on relative amounts of T cell subpopulations and TREC levels as determined 10 weeks after disease onset. Shown are the relative values of selected T cell subpopulations in PB of healthy control subjects (HC) and COVID‐19 convalescent patients (COVID‐19). Bars show mean values, whiskers the standard deviation, and open circles the values of single individuals. Data show pooled results of daily stainings (whole blood, 5‐9 individuals per day) and TREC analyses of n = 98 for HC, and n = 109 for COVID‐19 convalescent patients, except for panels determining CD25/Foxp3 n = 97 for HC; and CD45RO/CCR7 n = 95 for HC and n = 105 for COVID‐19. P‐values were determined by Mann‐Whitney U‐test and are indicated. TREC, T cell receptor excision circles

Figure 3

Impact of primary SARS‐CoV‐2 infection on relative amounts of Bcell subpopulations and KREC levels as determined 10 weeks after disease onset. Shown are the relative values of the indicated Bcell subpopulations in PB of healthy control subjects (HC) and COVID‐19 convalescent patients (COVID‐19). Bars show mean values, whiskers the standard deviation, and open circles the values of single individuals. Data show pooled results of daily stainings (whole blood, 5‐9 individuals per day of n = 78 for HC, and n = 108 for COVID‐19 convalescent patients)and KREC analyses (n = 98 for HC and n = 109 for COVID‐19). P‐values were determined by Mann‐Whitney U‐test and are indicated. KREC, kappa‐deleting recombination excision circles

Figure 4

Clinical symptoms of COVID‐19‐infected patients and their correlation with cellular and humoral immune parameters. A, Shown are the frequencies of symptoms observed in COVID‐19‐infected patients (n = 109). B to H, Shown are the correlations of cellular (B to E) and humoral (F to H) immune parameters with typical COVID‐19 symptoms (n = 85 in B; n = 109 in C; n = 23 for no and n = 84 for fever in D; n = 109 for E, F and n = 108 for G; n = 37 for no and n = 72 for loss of taste/smell in H). In B, only patients presenting with fever are shown. Statistical significance was determined by Mann‐Whitney U‐test for categorical values and by Pearson's correlation for continuous values. Lines in B, C and F to H represent the trend. COI, cut‐off index