When the immune system is exhausted
Imagine how exhausted we are after finishing a 10k run. We might want to cool down a bit to recover before doing any physical activities again.
But did you know that our immune system can be exhausted too? Yes, they can, and exhaustion is the keyword here. Immune exhaustion is real, and it’s not the same to what we feel after finishing a race.
Exhausted, but not worn out
Immune exhaustion does not mean our immune system is overworked or running out of energy. It means it cannot detect and react to any infectious agents or diseases. In other words, it’s irresponsive.
Should we freak out?
Yes, we should.
Our immune system is our body’s defence force against diseases. When it cannot do its proper work, our body is weaker. Immune exhaustion happens during disease development in our body, such as cancer and AIDS.
Smart cancer cells, happy cancer cells
Our immune cells are actually capable of combating cancer cells. One of the immune cells, cytotoxic T cells (Tc cells), can recognise cancer as a threat through an interaction with neoantigen on the surface of cancer cells. This interaction via neoantigen ends with (spoiler alert) cancer cells death.
But, cancer cells are smart. They know how to escape Tc cells radar.
Cancer cells overproduce a surface protein called protein-death ligand 1 (PD-L1). This protein, when binds to its pair called PD-1 on the surface of Tc cells, sends a deactivating signal to the Tc cells.
Naturally, PD-L1 – PD-1 interaction functions as a stop signal for Tc cells to avoid any autoimmune reaction to our body. Note that almost all cells in our body have PD-L1 on their surface, while cancer cells overproduce it.
However, as Tc cells activity might be harmful for cancer growth, cancer cells send the “brakes signal” as much as they can to Tc cells. Once shut down, Tc cells lose their ability to detect and kill cancer cells. In other words, they are exhausted.
As a result, cancer cells can grow rapidly, happily, and dangerously, without any threat from our body’s immune cells.
Scary isn’t it?
Boosting Immunity by Outsmarting Cancer
The solution of immune exhaustion is to prevent the interaction that causing it at the first place. Blocking the PD-L1 – PD-1 interaction can prevent Tc cells from “hitting the brakes”. Therefore, this blocking can boost our immune system and promote Tc cells anti-cancer activity.
Scientists have been busy testing new drugs, or what so called immune checkpoint inhibitors, as the blockade. Some drugs are already established and proven to be effective in skin, lung, and renal cancers. This therapy is a type of cancer immunotherapy.
However, it might take a while for scientists to cover other types of cancer. This is due to different conditions in different tissues. For example, brain cancer might be a bit of a challenge due to the Blood-Brain Barrier (I wrote about it on my previous blog!), which causes difficulties in drug delivery to cancer sites.
The good thing is, we know the cure of cancer is in our body. We just need to support it to outsmart the disease.