As for the correlation analysis of 28 immune cells containing the 6 biomarkers showed that in the COVID-19 dataset, LCK, PLCG1, and RASGRP1 were most significantly positively correlated with effector memory CD4 T cells, central memory CD4 T cells, and central memory CD8 T cells, respectively (P < 0.001). Here, CD4 is linked to COVID-19.