there is a rich immunological crosstalk between the brain and the rest of the
body, particularly via the meninges.
Collectively, these data confirm that there is a cellular and molecular immune
system of the brain. The actors and mechanisms just described come in addition
to various cell-intrinsic innate defense mechanisms used by neurons in case of
viral infections (Ordovas-Montanes et al. 2015).
Not only is there an immune system of the brain, but recent research confirms
that there are many interactions between the nervous and the immune system in
a healthy organism, with much richer communication pathways than initially
suspected (Figure 5.3). These interactions occur at various levels: molecules,
Figure 5.2 Immune communication between meninges and the brain.Apart
from microglia, immune cells are generally not present in the brain, as, in
nonpathological situations, they are thought to not cross the blood–brain barrier.
However, meninges contain lymphatic vessels and peripheral immune cells,
which communicate with the brain via cytokines. (Figure drawn by Wiebke
Bretting).
48 Elements in the Philosophy of Biology