A group of small proteins that act as signals to other cells to elicit some response (usually an immune response). For example, cytokines can be used as an alarm signal to recruit immune cells to an infection in the body.
There are different kinds of cytokines and they can be grouped depending on how they influence other cells.
These responses are called “Th1” or “Th2” and are named this way because T helper (Th) cells can secrete these cytokines.
- A Th1 response is pro-inflammatory (characterized by the cytokines IFN-gamma, IL-2, etc.)
- A Th2 response is anti-inflammatory (IL-4, IL-5, IL-10, etc.)
The type of cytokine environment, either Th1 or Th2, dictates how immune cells in that environment behave (ie. M1 macrophages are pro-inflammatory, M2 are anti-inflammatory). This is how the immune system can coordinate a defense against an infection.
For example, if there’s a bacterial infection, an immune cell will recognize that as a threat and secrete Th1 cytokines, like IFN-gamma. These cytokines will activate other immune cells in the environment, like macrophages or NK cells, so they can destroy the bacteria. When the threat is cleared, they can start secreting Th2 cytokines to reverse the Th1 response.
Some people could have imbalances of Th1 and Th2 cytokines, so the Th1/Th2 ratio is skewed to be more Th1. Although it’s controversial, this imbalance could cause increased activation of immune cells like NK cells, which could possibly lead to problems with implantation.