Final answer:
Cytokines are chemical messengers that regulate immune responses. IL-23 is an important cytokine in the immune response against extracellular pathogens and inflammation.
Step-by-step explanation:
Cytokines are chemical messengers released by cells of the immune system to regulate immune responses. In the context of extracellular pathogens and inflammation, cytokines play a key role in coordinating the immune response against invading pathogens. One important cytokine in this process is IL-23. IL-23 helps to activate and differentiate T cells, which play a crucial role in fighting against extracellular infections.