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Immunity: is the body´s ability to fight off harmful micro-organisms the immune system produces antibodies or cells that can deactivate pathogens. Fungi, protozoans, bacteria, and viruses are all potential pathogens Infectious disease :is one in which minute organisms, invisible to the naked eye, invade and multiply within the body. Many of these organisms are contagious , that is they spread between people in close contact An antibiotic : a protein produced in response to an antigen. ,is a chemical substance derivable from a mold or bacterium that kills microorganisms and cures infections . The Immune response the immune system does when confronted by an antigen.- An immune response is an elaborate interplay between antigen, non-specific defenses, and B and T lymphocytes.- Immune responses can be innate or adaptive.

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