The answer to both of these questions lies in knowledge of the lymphocytes of the immune system, and so it is on lymphocytes that this lecture will focus. To initiate our discussion, we need to define pathogens . This term refers to any disease producing agent. What is surprising about our defenses against disease is that they can work against so many diverse pathogens. Pathogens can be viruses, bacteria, fungi, protistans, and parasitic animals.
All animals have numerous nonspecific barriers against pathogens.
They generally work by preventing pathogen entry or by damaging the pathogens . An example of a barrier to pathogen entry is your skin. An example of a defense that damages pathogens is lysozyme , an enzyme that damages bacterial cell walls. Lysozyme is found in the tears in our eyes to protect our eyes from bacterial infection. Lysozyme is also found in the blood of insects to protect them against bacterial invasion should their cuticle be damaged.