TLR9 and Epstein-Barr virus infection: In cell culture, mitogens such as the TLR9 ligand CpG DNA as well as T cell derived CD40 ligand and IL-4 (CD40L/IL-4) promote B cell proliferation similar to EBV infection (Elgueta et al., 2009; Krieg et al., 1995; Nikitin et al., 2014) (Figure 4A–C).