your immune system might end up attacking your own
body, and voilà—autoimmunity develops.
Protecting Our Brains from What’s in Our
Guts
As I’ve mentioned earlier, the colon is where the majority of
bacteria in your gastrointestinal tract reside, giving the cells
that line it two important functions: serving as a blockade
against pathogens and bacteria that don’t belong in your
circulation, while also allowing for the absorption of fluids
and any remaining nutrients that haven’t been absorbed by
the small intestine. This physical barrier forms part of the
body’s innate immune system.
The innate immune system plays a major role in
mediating inflammation and autoimmunity. It helps keep the
microbiome and our immune cells (our adaptive immune
system) separate from each other, regulating host-microbial
interactions and maintaining appropriate immune function
on a constant basis. In our stadium metaphor, this allows the
game to go on as planned, ensuring a nice day for everyone
there. The guards can safely perform their jobs, the fans can
eat their hot dogs and cheer for their respective teams, and
the players can compete, allowing them to earn millions of
dollars in endorsement money. Physical barriers help make
all this possible.
The cells of the epithelium—your intestinal lining—are
held together by tight junctions that can open and close like
the drawbridge on a castle. Thankfully, they are closed most