A patient is exposed to a viral infection but shows no symptoms. After a few days, they develop a fever and localized swelling in the lymph nodes. Which innate immune response mechanism is primarily responsible for the fever and inflammation in this context?

When a virus infects the body, macrophages and dendritic cells recognize viral molecules and become activated. These cells release pro‑inflammatory cytokines such as interleukin‑1, interleukin‑6 and tumor necrosis factor‑α. The cytokines travel to the brain and raise the body’s set‑point temperature, producing a fever, and they also attract more immune cells to the lymph nodes, causing swelling. Thus, the primary innate mechanism is the cytokine‑mediated inflammatory response triggered by activated phagocytes. For example, a macrophage that sees viral RNA will release IL‑1, which signals the hypothalamus to increase body temperature and the lymph node to swell.