 In this video I will distinguish between innate and adaptive immunity. Inate immunity refers to the defense against infection that we are born with, and while innate immunity responds quickly, it is not specific for a particular pathogen. In contrast, adaptive immunity recognizes antigens associated with specific pathogens and forms an immunological memory. The innate immunity includes surface defenses. For example, the skin forms a physical barrier to pathogens. Even as we are breathing and draw air with pathogens into the respiratory tract, there is hair at the entrance to the nasal cavity that can help to filter pathogens out and serve as another surface defense. And then the respiratory tract is lined with a mucus membrane that secretes mucus. Mucus can trap pathogens, and mucus also contains defense proteins that can help protect against infection. There are also internal defenses that are part of our innate immunity, and this includes leukocytes such as mast cells and basophils. Mast cells are found in most connective tissue and can respond to infection, releasing inflammatory mediators such as histamine that will then stimulate inflammation to bring more leukocytes in to help defend against infection. And basophils also provide a similar function, releasing histamine to activate the inflammatory response, although basophils are found circulating in the blood. Natural killer cells are a type of lymphocyte that's part of the innate immunity, while most lymphocytes, the T lymphocytes and B lymphocytes, are part of the adaptive immunity. Natural killer cells can recognize viral infected cells and stimulate apoptosis of those cells in order to prevent the virus from spreading. While natural killer cells defend against viral infections, they're not specific for any particular virus. It would be the adaptive immunity that would respond to a specific strain of a virus by recognizing antigens associated with that virus. The natural killer cells instead recognize chemical signals that are associated with a viral infected cell in general, not a cell that's infected with a specific type of virus. There are also defense proteins. The complement system are defense proteins circulating in the blood that can bind to molecular patterns on the surface of pathogens, such as bacterial cells, and then form a membrane attack complex that will punch holes in the membrane of the bacterial cell, leading to the death of that cell and marking that cell for other defense mechanisms, such as phagocytic leukocytes. So, leukocytes that can perform phagocytosis also work as part of the innate immunity. These leukocytes will bind to pathogens and engulf the pathogens, then break down those pathogens to destroy the cell and protect against that infection. So, while all of these defenses of the innate immunity are quick to respond and help defend against infection, they're not as effective as the adaptive immunity can become. The adaptive immunity is a little slower, but when the adaptive immunity is activated, it can produce a coordinated response against a specific infection and develop immunological memory so that on a second encounter with the same pathogen, the immune response is more rapid and more vigorous, and ideally, we can become immune to that pathogen so that we won't get sick at all, even if we're exposed to it.