The immune system helps protect organisms from pathogens in their environment. It also does an important job of recognizing the microorganisms as well as the organs received through transplantation as foreign, creates antibodies that are specific to antigens (a foreign material that causes an immune response). This process helps protect organisms from pathogens such as disease-causing viruses, parasitic bacteria and fungi, and other infectious agents. Some defenses prevent these foreign invaders from entering the body, others help remove them, and yet others help fight the invaders.
Figure 1: Adaptive Defenses: Interactions in Specific Immune ResponseAdapted from Anjelica Gonzelez, Yale-New Haven Teachers Institute
The immune system is comprised of the Non-Specific defenses and Specific defenses. 7Non-Specific defenses (innate immunity) provide the first line of defense against pathogens. They include physical barriers such as the skin, defense mechanisms such as mucous membrane, tears, and sweat and low pH of the stomach acid and general immune responses such as fever and inflammation. Fever helps raise body temperature, which interrupts the reproduction of viruses and other pathogens. Inflammation allows the phagocytic cells such as macrophages and leukocytes to leak into the damaged tissue and helps engulf and destroy pathogens through a process called phagocytosis. The cells of the immune system include the phagocytes, macrophages, mast cells, neutrophils, eosinophils, basophils, natural killer cells, and dendritic cells. Their main job is to locate, identify, incapacitate, and kill the invaders.
8Specific defenses (adaptive immunity) are provided by the two types of lymphocytes, B cells, and T cells. T cells develop in the thymus and the B cells develop in the bone marrow of the long bones. B cells have membrane-bound antibodies on their surface. When they encounter a pathogen that fits or matches the antibodies on their surface, they quickly divide into a memory B cells and plasma cells. This process is called the antibody-mediated immune response. The plasma cells produce the same antibodies as the parent B cell and these antibodies circulate throughout the body searching for antigens but the memory B cells have the same membrane-bound antibodies as the parent B cell. Immunity is achieved through antibodies present in a person's body. Antibodies are proteins produced by the body to destroy toxins or disease-causing organisms (antigens). Antigens are disease-specific. Antibody molecules have two important jobs: binds to the specific antigen and activate specific defenses such as phagocytes that destroy the antigen.
When they encounter a pathogen that fits or matches the antibodies on their surface, they quickly divide into a memory B cells and plasma cells. This process is called the antibody-mediated immune response. The plasma cells produce the same antibodies as the parent B cell and these antibodies circulate throughout the body searching for antigens but the memory B cells have the same membrane-bound antibodies as the parent B cell. Immunity is achieved through antibodies present in a person's body. Antibodies are proteins produced by the body to destroy toxins or disease-causing organisms (antigens). Antigens are disease-specific. Antibody molecules have two important jobs: binds to the specific antigen and activate specific defenses such as phagocytes that destroy the antigen.
Figure 2: B cell and the Antigen-Antibody ComplexAdapted from Khan Academy
On the other hand, the T cells do not produce antibodies. There are two types of T cells: cytotoxic T lymphocytes and helper T cells, which play a major role in the cell-mediated immune response. The surface of the T cells is covered with proteins called T cell receptors. These T cell receptors only recognize only the surface proteins bound to the major histocompatibility complex (MHC) of macrophages and dendritic cells. As explained in the figure: 1, during phagocytosis cells such as macrophages ingest the pathogen, digest it, and then display portions of the pathogen’s proteins bound to their MHC proteins on their surface. The T cells, in turn, recognize the protein bound to the MHC proteins and then alert the cytotoxic T cells to orchestrate apoptosis (programmed cell death), which helps limit the spread of infection. Hence T cells play a vital role in distinguishing the MHC that belong to the organism’s own cells from that of foreign cells.