CD4 and infection: Regulated by specific cytokine milieu and transcriptional factors, activated CD4+ T cells have the potential to differentiate into various cellular subsets, including TH1, TH2, TH9, TH17, TH22, TH25, follicular helper T (TFH), and induced regulatory T (iTREG) cells (Figure 1), to deal with different types of infection or non-infection situations (O’Shea John and Paul William, 2010; Caza and Landas, 2015; Das et al., 2017; Umar et al., 2020).