CD4 and infection: Alveolar macrophages carrying an array of cytokines rush towards the site of infection; and the resident dendritic cells (DCs) facilitate the trapping of viral antigen which is processed for presentation by the major histocompatibility complex (MHC) I to CD8+ T cytotoxic cells (Tc) and MHC II to CD4+ T cells; and afterward the CD4+ T helper cells (Th) stimulate B cells (triggering antibody-mediated immune response), the CD8+ T cells (mediating cellular immune responses); and help in the development of memory cells (Noor 2021a, 2021c; Chung et al. 2021).