Question

Viruses can cross the blood-brain barrier a. by infecting immune cells which then cross the bloodbrain barrier b. by crossing as free virus c. by first attaching to brain endothelial cell glycoproteins d. by first attaching to receptors on brain endothelial cells e. all of the above

Short answer

a) Infecting immune cells b) Crossing as free virus particles c) Attaching to brain endothelial cell glycoproteins d) Attaching to receptors on brain endothelial cells e) All of the above Answer: e) All of the above

Step-by-step solution

Understanding the Blood-Brain Barrier

The blood-brain barrier (BBB) is a highly selective and protective barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system. It plays a crucial role in maintaining the brain's microenvironment and preventing potentially harmful substances from entering the brain.

Virus Interaction with the Blood-Brain Barrier

Viruses can cross the blood-brain barrier through different mechanisms such as infecting immune cells, crossing as free virus particles, or attaching to specific proteins or receptors located on the surface of brain endothelial cells.

Option A: Infecting Immune Cells

Some viruses can enter the brain by infecting immune cells (such as monocytes or macrophages) which are capable of crossing the blood-brain barrier. Once inside the brain, the infected immune cells can release the virus, allowing it to infect other cells in the brain. This mechanism is known as the "Trojan horse" mechanism.

Option B: Crossing as Free Virus

Some viruses can cross the blood-brain barrier as free virus particles without the need to infect immune cells. They can take advantage of certain transport systems or cross the endothelial cells of the blood-brain barrier directly through a process called transcytosis.

Option C: Attaching to Brain Endothelial Cell Glycoproteins

Some viruses can interact with specific glycoproteins on the surface of brain endothelial cells, allowing them to cross the blood-brain barrier. These viral interactions can either facilitate transcytosis or enhance the permeability of the blood-brain barrier, making it easier for the virus to enter the brain.

Option D: Attaching to Receptors on Brain Endothelial Cells

Attachment to specific receptors on brain endothelial cells is another way some viruses can cross the blood-brain barrier. By interacting with these receptors, viruses can trigger signaling pathways that increase the permeability of the barrier or facilitate transcytosis, thus allowing them to enter the brain.

Concluding the Answer

Based on the information provided above, it is clear that viruses can use several mechanisms to cross the blood-brain barrier, as described in options A, B, C, and D. Therefore, the correct answer is (e) all of the above.