Which of the following is NOT a function of the blood-brain barrier?

The blood-brain barrier (BBB) is a selective permeability barrier formed by endothelial cells in the brain's capillaries, effectively regulating the environment of the central nervous system (CNS). It serves several critical functions, the most notable being the protection of the brain from potentially harmful substances, such as toxins and pathogens. This barrier allows for the regulation of what substances can enter the brain while restricting harmful agents.

One of the primary roles of the BBB is to maintain the brain's microenvironment. It helps to ensure that neurotransmitters, ions, and other key molecules are present at the appropriate levels to support optimal brain function. Additionally, the BBB regulates the transport of essential nutrients, such as glucose and amino acids, making it vital for neuronal health and activity.

The function specified in the provided answer relates to the facilitation of immune cell access. While the blood-brain barrier does impede the entry of many immune cells into the brain to protect it from inflammation and potentially damaging immune responses, it is not designed to facilitate high access for these cells. Instead, the BBB acts to limit immune cell infiltration, thereby helping to maintain the unique environment necessary for normal brain function. This reduces the risk of inflammatory responses that could lead to neurological damage.

In summary