Which cytokine is primarily involved in initiating the innate immune response and inflammation?

• A. IL-1
• B. IL-2
• C. IL-4
• D. IL-10

Answer: (A)

Initiation of the innate immune response and inflammation relies on early proinflammatory signals released by sentinel cells, especially macrophages, when they detect pathogens. The cytokine that acts as a primary trigger is IL-1. When macrophages encounter microbial components, they release IL-1, which acts on endothelial cells to upregulate adhesion molecules, promoting neutrophil recruitment to the site of infection. IL-1 also drives fever through effects on the hypothalamus and stimulates the liver to produce acute-phase proteins, amplifying the inflammatory response. This early signaling sets the stage for the rest of the inflammatory cascade and further innate immune activation. Other cytokines listed have different primary roles: IL-2 mainly supports T cell growth and activation in the adaptive response; IL-4 promotes a Th2/humoral response; IL-10 functions to limit and resolve inflammation rather than initiate it.