Fig 1.
Ways viruses can use to cross the BBB.
Illustration of a blood vessel and the four nonexclusive ways viruses may employ to reach adjacent tissues: 1. Diffusion (passive-aggressive way): Viruses freely diffuse when endothelium integrity is altered. 2. Infection (energetic way): The endothelium is infected and viruses released on the other side. 3. Transcytosis (commuting way): The circulating virions are endocytosed by endothelial cells and exocytosed on the other side, in the absence of productive infection. 4. Cell transport (Trojan horse way): Leukocytes are carrying the circulating viruses through the endothelial cell wall. BBB, blood–-brain barrier.