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

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Even ten weeks after disease COVID‐19 convalescent patients had fewer neutrophils, while their cytotoxic CD8<jats:sup>+</jats:sup> T cells were activated, reflected as higher HLA‐DR and CD38 expression. Multiparametric regression analyses showed that in COVID‐19‐infected patients both CD3<jats:sup>+</jats:sup>CD4<jats:sup>+</jats:sup> and CD3<jats:sup>+</jats:sup>CD8<jats:sup>+</jats:sup> effector memory cells were higher, while CD25<jats:sup>+</jats:sup>Foxp3<jats:sup>+</jats:sup> 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<jats:sup>+</jats:sup> 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<jats:sup>+</jats:sup>CD45RA<jats:sup>+</jats:sup>CD62L<jats:sup>+</jats:sup>CD31<jats:sup>+</jats:sup> recent thymic emigrants was associated with a loss of sense of taste and/or smell.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>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.</jats:p></jats:sec>