Our skin has its own distinct immune system
Our immune system plays a critical role in recognizing, fighting, and preventing infections, but now we’ve discovered that our skin has its own!
Our skin and mucosa are our first line of defense against infection with deadly pathogens.
But these surfaces and membranes aren’t sterile environments!
They’re teeming with biological activity and because they provide this “barrier” function, they’re constantly fending off infection from pathogenic microbiota.
And we call this a barrier, because that’s exactly what it is!
Our mucosa are like a moat around a castle that slows down any invaders (or drowns them if they can’t swim!)
And our skin is like the castle wall, helping to physically prevent big and small things from entering our bodies.
But that’s not where our skins’ defenses stop!
We’ve known for some time that the immune system is active in the skin and that it plays a vital role in managing the communities of microbes that live in and around our bodies.
This is important, because not all of the microbiota that we encounter are bad!
So our immune system has to play this tricky dance of letting the good guys in and keeping the bad guys out.
We now know that it does this using its own localized immune regulatory system!
In this week’s paper, researchers showed in mice that the skin has its own immune system that acts (mostly) independently.
In the figure above they a) painted a commensal (good) bacteria, S. epidermis, onto the skin of wild-type mice (WT), Bcl6Flox/cd4cre mice that can’t make B cells (make antibodies), µMT mice that can’t make T Helper cells (stimulate b cells to make antibodies), and Ltα-/- mice that lack secondary lymph nodes. Mice were then injected with S. epidermis 45 days later to see their immune response (a,b,c graphs). WT and mice lacking secondary lymphnodes mounted a strong response while mice who couldn’t make antibodies did not! d) is a control showing IgG production was the result of TA and not infusion e) shows representative bacterial growth from the serum of infused mice and f) is an overview of how the skin immune system works!
In this scheme, Langerhan’s cells (LCs) see antigens that collect in the hair follicle. This activates t-helper cells (Treg to TFH) that create complexes with b cells to form a germinal center like structure (where b cells grow up to make and secrete antibodies). These antibodies are then secreted into the follicle to protect the skin and into systemic distribution to the rest of the body.
So, the skin isn’t just some simple barrier!
It is a major part of our lymphatic system helping to make, distribute, and protect the entire body against infection!
In a second paper, the team modified S. epidermidis to display a piece of the tetanus toxin to the skin’s immune system and showed that this could be used to vaccinate mice against tetanus infection.
The implication here (if it all works the same in humans) is pretty mind blowing: needle free vaccines could be closer than many of us ever imagined!