Abhilash Pilli

Unit 1- Fish Immunology General concepts in immunology Immunology is the study of the immune system and its responses to invading pathogens. The immune system includes the molecules, cells, tissues, and organs that are associated with immunity in the host defense mechanisms. The coordinated reaction of these cells and molecules to invading pathogen is called immune response. The organs of the immune system are positioned throughout the body. They are called lymphoid organs. The generation of an immune response of either the innate or acquired variety requires the interaction of specific molecules, cells, and tissues. The immune system of fish is almost similar to that of higher vertebrates. Immunity is referred as the state of acquired or innate resistance or protection from a pathogenic microorganism or its products or from the effect of toxic substances. The cells of the immune system consist of lymphocytes, specialized cells that capture and display microbial antigens, and efffector cells that eliminate pathogens. Microorganisms in the environment are blocked by physical barriers like skin, mucus etc from being enter into the host. If the pathogens overcome this barrier and invade the host the innate immune mechanism is activated and destroys the pathogen. If the pathogen survives the innate immunity the adaptive immunity is activated and combats the pathogen, added to it adaptive immunity also keeps the memory of the pathogen which helps the immune system during the secondary invasion of the same pathogen. Host defense mechanisms consist of innate immunity and adaptive immunity. Nonspecific immunity is a fundamental defence mechanism in fish. Non specific immunity also plays a key role in activating acquired immune response.