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Answer to q. 1
Antigens are molecules on the outer surface of cells. Bacterial cells have them, your cells have them, so do viral particles, fungal cells, or even parasitic worms. They derive their name from the contraction antibody-generator. When an invading bacterium, some tumor cells, or cells from a transplanted organ are encountered, their specific molecules, the antigens, trigger the production of antibodies. Every different strain of influenza or cold has different antigens, so when you get two colds in one winter, your body became sensitized to the antigens of the first cold, but when presented with the second cold, it had different antigens, so it yet again took several weeks for your body to mobilize the forces to fight this second infection. Antigens on transplanted organs are different from those on the recipient's cells, so the recipient may have to take immune-suppressive drugs forever to prevent the immune system from rejecting a transplanted organ based on its different antigens. Antigens are typically protein molecules, but may be carbohydrates or lipids.
Answer to q. 2
Inflammation manifests itself as redness, pain, heat, and swelling. Damaged cells produce inflammation mediators that attract macrophages, a type of phagocyte. Inflammation mediators include complement, prostaglandins, and cytokins, all with the same ultimate result: attracting phagocytes. Histamines cause the capillaries to dilate, and the capillaries leak fluid (plasma), and some white blood cells (particularly phagocytes) also slip out. The accumulation of fluid adds to the swelling. Mucous-producing cells (goblet cells) also produce mucous at the site of infection, causing, for example, the nose to run.
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