Front. Immunol. | doi: 10.3389/fimmu.2021.619906
13. Feng Y et al. COVID-19 with different severities: A multicenter
study of clinical features. Am. J. Respir. Crit. Care Med.2020;201(11):1380–1388.
14. Diao B et al. Reduction and Functional Exhaustion of T Cells in
Patients With Coronavirus Disease 2019 (COVID-19). Front.
Immunol. 2020;11(May):1–7.
15. Chen G et al. Clinical and immunological features of severe and
moderate coronavirus disease 2019. J. Clin. Invest.2020;130(5):2620–2629.
16. Huang W et al. Lymphocyte Subset Counts in COVID-19 Patients: A
Meta-Analysis. Cytom. Part A 2020;97(8):772–776.
17. Padgett LE et al. Interplay of monocytes and T lymphocytes in
COVID-19 severity. bioRxiv 2020; doi:10.1101/2020.07.17.209304
18. Sakaguchi S et al. Regulatory T Cells and Human Disease. Annu.
Rev. Immunol. 2020;38(1):541–566.
19. Chevalier MF, Weiss L. The split personality of regulatory T cells
in HIV infection. Blood 2013;121(1).
doi:10.1182/blood-2012-07-409755
20. Galván-Peña S et al. Profound Treg perturbations correlate with
COVID-19 severity. bioRxiv 2020; doi:10.1101/2020.12.11.416180
21. Kennedy JJ, Steain M, Slobedman B, Abendroth A. Infection and
Functional Modulation of Human Monocytes and Macrophages by
Varicella-Zoster Virus. J. Virol. 2018;93(3).
doi:10.1128/jvi.01887-18
22. Prabhu VM et al. Monocyte Based Correlates of Immune Activation and
Viremia in HIV-Infected Long-Term Non-Progressors. Front.
Immunol. 2019;10(December):1–15.
23. Müller TM et al. Circulating Adaptive Immune Cells Expressing the
Gut Homing Marker α4β7 Integrin Are Decreased in COVID-19. Front.
Immunol. 2021;12(April):1–11.
24. Arunachalam PS et al. Systems biological assessment of immunity to
mild versus severe COVID-19 infection in humans. [Internet].Science 2020;6261(August):1–18.
25. Dienz O et al. The induction of antibody production by IL-6 is
indirectly mediated by IL-21 produced by CD4 + T cells. J. Exp.
Med. 2009;206(1):69–78.
26. Eto D et al. IL-21 and IL-6 are critical for different aspects of B
cell immunity and redundantly induce optimal follicular helper CD4 T
cell (Tfh) differentiation. PLoS One 2011;6(3).
doi:10.1371/journal.pone.0017739
27. Kasarpalkar NJ, Bhowmick S, Patel V, Savardekar L. Frequency of
Effector Memory Cells Expressing Integrin α 4 β 7 Is Associated With
TGF- β 1 Levels in Therapy Naïve HIV Infected Women With Low CD4 + T
Cell Count. Front. Immunol. 2021;12(March):1–12.
28. Bergamaschi C et al. Intracellular interaction of interleukin-15
with its receptor α during production leads to mutual stabilization and
increased bioactivity. J. Biol. Chem. 2008;283(7):4189–4199.
29. Inoue S et al. IL-15 Prevents Apoptosis, Reverses Innate and
Adaptive Immune Dysfunction, and Improves Survival in Sepsis. J.
Immunol. 2010;184(3). doi:10.4049/jimmunol.0902307
30. Kandikattu HK, Venkateshaiah SU, Kumar S, Mishra A. IL-15
immunotherapy is a viable strategy for COVID-19. Cytokine Growth
Factor Rev. 2020;54(May):24–31.
31. Abers MS et al. An immune-based biomarker signature is associated
with mortality in COVID-19 patients. JCI Insight 2021;6(1).
doi:10.1172/jci.insight.144455
32. Angioni R et al. Age-severity matched cytokine profiling reveals
specific signatures in Covid-19 patients. Cell Death Dis.2020;11(11). doi:10.1038/s41419-020-03151-z
Table 1. Abridged clinical data of study participants