When your body encounters a foreign object, known as a pathogen, the cascade of events that follows is called innate immunity. This is the ability of your immune system to locate and destroy anything that isn’t native to your body. The adaptive immune system is much more complex. It comprises the mechanisms that enable your body to record a random innate response and encode it into new lymphocytes that will be ready when that specific pathogen is encountered again in the future.
In this way, it is a sort of immune memory that enables your body to respond much quicker and more devastatingly to something it already knows to be a dangerous pathogen. The bridge between innate and adaptive immunity, where your body memorizes an innate response to a pathogen, takes place during the inflammatory response. Check out our article about innate immunity to get some background on this complicated process before you read on.
What is the inflammatory response?
In addition to fighting off foreign invaders, our immune system also mediates pain and injury. Anytime there is physical injury, from a papercut to a broken bone, the immune system immediately reacts. Just like B-cells respond to antigens that are foreign to the body, they also respond to distress proteins from our body’s own cells.
When damage occurs to tissue, hormones and other inflammatory factors explode out of the damaged cells and attract white blood cells nearby to bring nutrients to the site. One of these factors is the endocannabinoid 2-AG, which arouses and initiates several cellular processes. Others cause nearby capillaries to expand allowing for greater blood flow, and they agitate nerve cells in the vicinity which generally results in pain that makes you favor the injured body part. The heightened metabolism at the site induces coagulants to rush to the area to stop any bleeding and provide structure that will eventually form scar tissue.
These immune responses happen automatically, and we have understood little about the underlying mechanisms that power their intricacy and automation. However, there is an erupting body of research shedding light on the role of the endocannabinoid system in mediating these processes and allowing your system to maintain internal homeostasis amid wildly fluctuating external circumstances.
What is adaptive immunity?
When an inflammatory response occurs, the complicated mixture of hormones, proteins, and cell signals tell white blood cells to gather up everything that looks foreign and get rid of it. When a B-cell finds a pathogen it binds to, let’s say strep, it becomes activated.
It begins replicating because it and its offspring are the only B-cells equipped to take out the army of strep. Other lineages of B-cells bind with different pathogens. In addition, the strep-activated B-cell and its replicants will take antigens from the dead strep cell and present them on their surfaces in what’s called an MHC II protein. MHC II strongly attracts other lymphocytes called T-cells, and this causes an explosion of cellular activity and metabolism that leads to the physical swelling and rise in temperature characteristic of inflammation. The production of this extremely important protein is mediated by the endocannabinoid system.
If you have encountered strep before, then the process I’m about to describe has already occurred and T-cells which possess strep antibodies are already finding and eradicating it. But how do these cells get the right antibody in the first place…
If strep is new to your system, then:
- An inactive T-cell, seen floating in the graphic above, binds to strep antibodies (green) held by the MHC II protein (pink) on the surface of an activated B-cell. Every MHC II complex is identical, but the antibodies that it holds are unique to one specific pathogen, in this case, strep.
- The T-cell becomes activated, and begins to produce antibody proteins like the one that activated it. It makes copies of its newly-immune-to-strep self, and rushes to destroy every strep pathogen in the body.
After the battle has calmed down, endocannabinoid receptors become active with a different endocannabinoid, anandamide, that has the opposite effect of 2-AG. Instead, anandamide causes the T-cells to begin to die off so that the swelling reduces and everything returns back to normal.
However, a select few T-cells, called memory T-cells (mT-cells), remain alive, circulating in your bloodstream and lymph system. These cells make up the army that will destroy that strep immediately, without any of the chaos you just read about, when it’s encountered again in the future. This is a very basic description of adaptive immunity, and this is why vaccines contain deactivated viruses or bacteria: so without getting sick, our body can still create and store antibodies, creating immune cells that are ready to fight that specific pathogen if and when it’s encountered in the future.