Focusing on Adaptive Immunity The Immune System Focusing on Adaptive Immunity

Objectives Identify immune system anatomy Differentiate between innate immunity and adaptive immunity Describe antibody-mediated immune response and its function Describe cell-mediated immune response and its function Understand the effect of HIV infection on the immune system

Overview The body’s ability to protect itself is known as immunity Pathogens are disease causing cells. These can include: Viruses, bacteria, parasites, allergens, etc. Defective cells in the body that threaten to do harm, such as cancer. Immunogens are substances that trigger the body’s immune response Antigens are immunogens that react with products of the immune response

Brief Immune System Anatomy Adenoids: Two glands located at the back of the nasal passage. Blood vessels: The arteries, veins, and capillaries through which blood flows. Bone marrow: The soft, fatty tissue found inside bones where blood cells are made. Lymph nodes: Small organs shaped like beans, which are located all over the body and connect via the lymphatic vessels. Lymph vessels: A network of channels all over the body that carry lymphocytes to the lymphoid organs and bloodstream. Peyer's patches: Lymphoid tissue in the small intestine. Spleen: A fist-sized organ located in the left side of the belly. Thymus: A small organ behind the breastbone. Tonsils: Two oval masses in the back of the throat. The immune system is mostly integrated into the tissues of other organs, such as the skin and gastrointestinal tract. Two components: lymphoid tissue and cells responsible for immune response Lymphoid tissue is found all over the body. Primary lymphoid tissues are the thymus gland and the bone marrow. All the cells of the immune system are created in the bone marrow Anatomically, the immune system is positioned wherever pathogens are most likely to enter the body. https://www.hopkinsmedicine.org/healthlibrary/conditions/infectious_diseases/immune_system_85,P00630

The Body’s First Line of Defense Barriers that protect external pathogens from entering the body: Skin, tears, mucus, and stomach acid. If barriers are evaded, an immediate internal immune response is initiated: Detection and identification of the pathogen, Communication with other immune cells to rally an organized response, Recruitment of assistance and coordination of the response among all participants, and Destruction or suppression of the pathogen.

The Internal Immune Response Innate immunity is present at birth and is the immediate response to pathogen invasion. It is not specific to any one pathogen. This response is not remembered by the immune system and will be triggered again with each exposure. Adaptive immunity is the body’s specific immune response by acting on particular pathogen invaders. It is the slower response and can take days to weeks after first exposure. Can be divided into cell-mediated immunity and antibody-mediated immunity (also known as humoral immunity).

Cell-mediated responses Antibody-mediated responses: Antibodies Destroy or suppress the pathogen Adaptive immune response: slow, specific, memory Cell-mediated responses B lymphocytes T lymphocytes Antibody-mediated responses: Antibodies Innate immune response: rapid, nonspecific, no memory Cells: Macrophages Neutrophils Natural killer cells Dendritic cells Eosinophils Basophils Chemical: Complement Interferons Barriers Physical: skin, mucous and other secretions Mechanical: flushing mechanisms such as cilia, fluid flow Chemical: enzymes and antibodies; pH Pathogen exposure

Summary The three major functions of the immune system: It tries to recognize and remove abnormal body cells created when normal cell growth and development go wrong. It removes dead or damaged cells, as well as old red blood cells. It protects the body from disease-causing pathogens.

Adaptive Immunity Adaptive immune responses are antigen-specific events. The body recognizes a particular foreign substance and selectively reacts to it. Macrophages and dendritic cells are the primary antigen-presenting cells Activate lymphocytes for the adaptive response.

Lymphocytes Adaptive immunity is primarily mediated by lymphocytes Varying receptors that are specific to a different antigen Three main types of lymphocytes: B lymphocytes, T lymphocytes, and natural killer (NK) cells.

Activate to effector cells Lymphocytes B cells Activate to effector cells Memory cells: initiate more rapid secondary response Plasma cells: secrete antibodies Long-lived plasma cells: secrete low levels of antibody for continued immunity Natural killer cells: destroy virus infected cells and antibody-tagged pathogens T cells Cytotoxic T (Tc) cells: kill cells displaying MHC-antigen complexes Helper T (TH) cells: activate other lymphocytes Regulatory T (Treg) cells: prevent excessive immune responses by suppressing other lymphocytes B cells mature in the bone marrow T cells mature in the thymus

Humoral Immunity The initial exposure of a naïve lymphocyte to its antigen triggers a primary immune response. The activated lymphocytes undergo clonal expansion. Cell division creates new effector cells. B cells differentiated into plasma cells Synthesize and secrete antibody molecules in plasma cells. The primary immune response slow and small in magnitude. The surface of every mature B lymphocyte is covered with as many as 100,000 antibody-like B cell receptors. This arrangement leaves the arms of the receptors available to bind free-floating extracellular antigens.

Humoral Immunity Once the pathogen has been resisted, the short-lived plasma cells die off. Long-lived plasma cells remain in the bone marrow to provide continued immunity. B cells differentiated into memory cells stay alive and wait for the next exposure of the same antigen. The subsequent exposures to the same pathogen trigger a secondary immune response. This response is faster and larger

Humoral Immunity Active immunity Passive immunity Occurs when the body is exposed to a pathogen and produces its own antibodies Can occur naturally, when a pathogen invades the body Can occur artificially Vaccinations containing dead or disabled pathogens Passive immunity Occurs when the body acquires antibodies made by another organism Example: the transfer of antibodies from mother to fetus across the placenta

Cell-Mediated Immunity T cell receptors only bind to antigens displayed on MHC proteins on target cells. The subtype of T cell determines the immune response. Cytotoxic T (Tc) lymphocytes defend the body against intracellular pathogens. Attack and destroy cells that display MHC-I-antigen complexes. Prevents reproduction of intracellular invaders. Viruses, some parasites, and some bacteria T lymphocytes have T cell receptors into their cell membranes. Once a pathogen gets inside a host cell, antibodies are no longer effective because they can only bind to soluble or exposed antigens Two ways cytotoxic T cells kill their targets: Apoptosis via pore-forming molecule perforin along with granzymes Apoptosis by activating Fas, a death receptor protein on the cell membrane linked to apoptosis enzyme cascade Cytotoxic T cells also give rise to memory T cells which wait for the next exposure to the same antigen

https://immuno-oncologynews https://immuno-oncologynews.com/2015/06/09/pd-1-protects-t-cells-burning/

Cell-Mediated Immunity Helper T cells and regulator T cells do not directly attack pathogens and infected cells. Both bind to antigens presented on MHC-II complexes. Helper T (TH) cells secrete cytokines to influence other immune cells B cells Cytotoxic T cells Regulatory T (Tregs) cells suppress immune cell function to help prevent excessive immune responses. HIV preferentially infects and destroys helper T cells, leaving the host unable to respond to pathogens that could easily be suppressed. Cytokines: protein signal molecules released by one cell that affect the growth or activity of another cell

Helper t cell: http://bodell. mtchs

Autoimmune Disease Autoimmune disease is caused by the body’s attack on its own cells. The body makes antibodies against its own components These antibodies are specific against a particular antigen and are usually restricted to a particular organ or tissue type. Common autoimmune diseases: Type 1 diabetes mellitus Multiple sclerosis Rheumatoid arthritis Systematic lupus erythematosus