CD2 and influenza: CellTrace Violet (CTV) labeled PBMC were cultured for 6 days using separate negative control cultures (medium only), positive control cultures with optimal T cell polyclonal antibody activation (CD3/CD28/CD2), as well as other cultures for proliferative responses to various recall antigens from infectious agents, including (i) influenza vaccine antigen; (ii) M. avium intracellulare lysate; and (iii) SARS-CoV-2 spike protein, respectively (Figures 3D–3F).