Acquired Immunity: Antigens, Antibodies, and Lymphocytes PDF

Biology 11 Acquired (adaptive) Immunity Involves the use of antibodies to fight a pathogen Antigens ​ surface substances such as lipids, carbohydrates and proteins, that are capable of stimulating a specific immune response ​ They are chemical markers that signal the b...

Biology 11 Acquired (adaptive) Immunity Involves the use of antibodies to fight a pathogen Antigens ​ surface substances such as lipids, carbohydrates and proteins, that are capable of stimulating a specific immune response ​ They are chemical markers that signal the body to produce antibodies ​ foreign antigens originate outside the body i.e. on pathogens ​ autoantigens originate within the body i.e. your cells Antibodies – Y-shaped proteins produced by special lymphocytes ​ Each antigen causes the production of a specific antibody that only attaches to that specific antigen ​ The antibodies have to be the right shape to match the antigens ​ Antibodies can also attack toxins and prevent them from attaching to a cell and interfering with its function ​ The average human body contains more than 10 million different antibodies ​ A properly functioning immune system can fight off a pathogen without feeling any symptoms Biology 11 Lymphocytes The key cells of the adaptive immune system are lymphocytes (a type of WBC) - cells that help the body destroy pathogens and allow the body to remember and recognize previous invaders There are two kinds of lymphocytes that are involved: 1.​ B-lymphocytes (B- cells) – mature in the bone marrow and are responsible for producing antibodies 2.​ T-lymphocytes (Helper T-cells & killer T-cells) - mature in the thymus gland (a specialized organ of the immune system – located behind the breastbone and in front of the heart) ​ Helper T- cells: responsible for regulating the production of antibodies by B-cells ​ Killer T-cells: destroy cells directly Biology 11 The Humoral Response (in the body’s fluids) 1. Antigen presentation ​ When a pathogen invades the body, a type of phagocyte called a dendritic cell engulfs some of the pathogens and presents the antigens on its surface (other cells may also display antigens such as B-cells and macrophages) 2. T-cell activation ​ This activates a small fraction of the body’s helper T-cells (those with the correct receptors that match the antigen) ​ Some of these cells become __________-T cells, others become effector T-cells 3. B-cell activation and differentiation ​ … activate B-cells by binding to them ​ The activated B-cells proliferate and differentiate into plasma cells and memory cells (colonial differentiation) ​ Plasma cells – produce and release antibodies (2000/s) into the bloodstream ​ causes the destruction of pathogens and infected cells by binding to antigens and making them easier targets for phagocytes ​ The production of antibodies from the first exposure to an antigen is known as the primary immune response ​ Memory cells – will produce antibodies at a much faster rate should the same pathogen invade in the future ​ This is known as the secondary immune response ​ More powerful than the primary response, memory B-cells produce antibodies so quickly that the disease never gets a chance to develop ​ The first exposure to a pathogen therefore causes the body to produce antibodies that can be used in future attacks by the same pathogen Biology 11 Cell-Mediated Immunity (Action by cells towards cells) ​ Some helper T-cells can attack infected antigen-bearing cells directly (killer T-cells) and therefore destroy the pathogens within. ​ Also known as – cytotoxic T-cells ​ Killer T-cells cause the pathogen to rupture and die (apoptosis – “cell death”) ​ Killer T-cells are also responsible for the rejection of tissue transplants