Virus-specific CD4+ T cells (T), virus-specific CD8+ T cells (E), the innate immune response captured by IFI27, IFI6, and IFI16 expression (F1, F2, F3, respectively), and anti-spike IgG each are assumed to have constant rates of production and per-capita natural death rates that maintain an equilibrium in the absence of infection. The gene discussed is CD4; the disease is infection.