Reduced frequency of T helper 17 and T helper 1 cells and their association with critical coronavirus disease 2019.

There is very little knowledge about the immune responses, particularly cellular immunity to coronavirus disease 2019 (COVID-19). The main objective of this study was to evaluate the frequency of T helper (Th) cell subtypes, including Th1, Th17, and Treg cells, in moderate-to-severe and critical COVID-19 patients compared to healthy controls. Twenty-nine moderate-to-severe and 13 critical patients confirmed for COVID-19, and 15 healthy subjects were included in this study. Interferon-I³ (IFN-I³)-producing Th1 and interleukin-17A-producing Th17 and Treg cells in peripheral blood were measured with flow cytometry. The frequency of Th1 and Th17 was significantly decreased in critical patients compared to healthy subjects (aMD: -2.76 and - 2.34) and moderate-to-severe patients (aMD: -1.89 and - 1.89), respectively (p < 0.05). Differences were not significant between moderate-to-severe patients and healthy subjects for both Th1 (p = 0.358) and Th17 (p = 0.535), respectively. In contrast, significant difference was not observed between study subjects regarding the frequency of Treg cells. Patients with critical COVID-19 had a markedly lower Th1/Treg and Th17/Treg ratios compared with the controls and moderate-to-severe cases. Our study showed a dysregulated balance of Th1 and Th17 cells and its relation to the severity of COVID-19.