Severity of COVID-19 Infectious and Immune-Based Profile

 Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes immune system dysregulation and a systemic cytokine storm. Under healthy conditions, T helper cells protect against intracellular pathogens, extracellular parasites, and extracellular bacteria.

 For the novelty of our study, little is known regarding the balance of T cell subtypes and responses in two forms of COVID-19 in our country. We investigated whether there was a relationship between T cell subtype frequency and cytokines by COVID-19 severity.

 Forty-six PCR-confirmed severe (n = 30) and moderate (n = 16) COVID-19 patients and 13 sex- and age-matched healthy control (HC) subjects were enrolled. Immunophenotyping of T cell subsets and related serum cytokines was performed using flow cytometry and ELISA, respectively.

 There was a significantly lower frequency of CD8+Tbet+ (P < 0.01) T cells in the severe group compared to HC. Also, there was a significantly lower frequency of CD4+GATA3+ (P < 0.001) and CD8+Tbet+ (P < 0.001) T cells in the severe group compared to the moderate group. Moreover, receiver-operating characteristic (ROC) curve analysis revealed a considerable correlation between CTL (CD8+T-bet+) subtypes and the severity of the disease. Severe COVID-19 disease was associated with reduced interferon-gamma (IFN-γ) and interleukin (IL)-2 concentration and increased IL-5 and IL-6 concentration.

 Reduced systemic levels of IL-2 can trigger decreased numbers of Th1 and Th2 cells, and in contrast to elevated IL-5 and IL-6, the numbers of Th2 cells did not increase in these cases.