CD4 and infection: During meningitis caused by E30 infection, viruses may interact with two major CNS barriers: the blood–brain barrier (BBB) and the blood cerebrospinal fluid barrier (BCSFB), while E30 infection has been shown to increase the migration of naïve T cells, including CD3+, CD4+, and CD8+, in the BCSFB (Dahm et al., 2018; Wiatr et al., 2019).