A study by Han, Ma [80] found that, compared to non-diabetic COVID-19 patients, the counts of total T lymphocytes (non-diabetic patients: 962.0 × 106/L, diabetic patients: 448.0 × 106/L), CD4+ T cells (non-diabetic patients: 583.0 × 106/L, diabetic patients: 204.0 × 106/L), CD8+ T cells (non-diabetic patients: 352.0 × 106/L, diabetic patients: 115.0 × 106/L), and NK cells (non-diabetic patients: 252.0 × 106/L, diabetic patients: 35.0 × 106/L) were significantly suppressed in diabetic patients with novel coronavirus pneumonia. Here, CD4 is linked to COVID-19.