ATF4 and COVID-19: Beyond this, other important pathways, including cell cycle metabolism (biosynthetic, catabolic, and cell cycle regulation pathways), response to glucose and lipids, oxidative stress (ER stress, unfolded protein response), and cellular homeostasis, were also found to be enriched in the upregulated DEGs (PPP1R15A, RGCC, IRS2, HSP90AA1, MT2A, MT1E, MT1X, ATF4, RHOA, PPBP, and PF4) within COVID-19 patients in activated CD4+ T cells compared to the healthy and recovered individuals, which indicate the response to a stimulus.