The reason one feels sick is because the bacteria found in the food were able to make a colony despite the innate defenses of the immune system such as the gut biome. As the bacterial colony is established, it creates an environment that is beneficial to the bacteria, but not beneficial to the surrounding tissue. This leads to cell death of the tissue. Upon cell, there are chemical markers released and enter the surrounding tissue and then the blood stream. Both of these signal to nearby and far off cells and tissues that there is somerhing happening and the cellular immune system, white blood cells, responds. These white cells have a host of defenses including raising the body’s temperature resulting in a fever.

From here many things can happen, but in the case of most healthy people in the developed world, the type of bacteria faced in food poisoning will be dealt with with little need for any medication that directly assists the immune response. Staying hydrated helps and mitigating digestive discomfort are the best things.