We hypothesized that the reduced numbers of CD4+ T-lymphocyte functional subsets and CD8+ T-lymphocyte functional subsets in patients with COVID-19 may be related to the overconsumption of CD4 + CD28+ T-lymphocytes and CD8 + CD28+ T-lymphocytes due to the attack of SARS-CoV-2 on the organism and/or to the dysfunction of the activation of T-lymphocytes caused by SARS-CoV-2 entry into the human body, and also to the dysfunction of the activation of CD4+ T-lymphocytes and CD8+ T-lymphocytes. Here, CD28 is linked to COVID-19.