Hot due to increased metabolism and blood flow. This helps to inhibit bacterial or viral reproduction. Swollen due to fluid leaking from the capillaries which will travel back through the lymph system. A moderate fever helps fight infections in several ways. Speeds the attach of phagocytes on pathogens.
Interferons are more efficient.
The liver and spleen are activated to clear iron from the blood. Since iron is needed for most bacteria to reproduce, the reduction in iron reduces the bacterial population. Recognizing self from non-self. The immune response is mounted against specific agents and a memory of the agent is retained in order to mount a vigorous defense if the invader reappears later in life. Immune response involves antigen, antibodies and cell mediated responses.