Immune System
Types of Immunity innate immunity acquired immunity defenses present before exposure to pathogens effective from birth acquired immunity defenses that develop after exposure to infectious agents & other foreign substances
Innate Immunity – External Defenses intact skin mucous membranes lining digestive, respiratory, & urinary tracts
Innate Immunity – Internal Defenses phagocytes cells that engulf microbes 4 types: neutrophils, macrophages, eosinophils, dendritic cells antimicrobial proteins enzymes that digest microbes inflammatory response see next slide
Inflammatory Response when tissue becomes damaged, histamine is released which triggers the dilation & increased permeability of nearby capillaries this promotes blood flow to the injured site which helps deliver antimicrobial proteins, clotting elements, & phagocytes to the injured area as blood rushes to the injured area, it turns red & heats up as fluid leaks out of the capillaries, the injured area swells
Acquired Immunity acquired immunity is highly specific because lymphocytes (a type of white blood cell) are capable of recognizing different types of inducing agents (antigens) antigens have specific binding sites called epitopes that lymphocytes (or the antibodies they secrete) recognize
Lymphocytes develop in bone marrow if they mature in the bone marrow, they become B cells if they migrate to the thymus to mature, they become T cells elicit two general types of responses: B cells secrete antibodies that circulate in the blood & lymph and bind to microbes, marking them for elimination (humoral response) T cells are cytotoxic lymphocytes that directly target and destroy infected cells (cell-mediated response)
Lymphocyte Receptors B cells have Y-shaped receptors with antigen-binding sites at the two tips of the “Y” these binding sites recognize intact antigens that circulate in the body ( B cells target extracellular pathogens) T cells have I-shaped receptors with one antigen-binding site these binding sites recognize antigen fragments bound to surface proteins on infected cells ( T cells target intracellular pathogens)
Primary Immune Response when an antigen binds to a lymphocyte, the lymphocyte is activated & gives rise to thousands of clones specifically targeted for that antigen (clonal selection) some of these clones are short-lived (effector cells) & go straight to “battle” others are long-lived (memory cells) & wait for future infections by the same antigen the primary immune response peaks ~10-17 days after initial exposure to the antigen
Clonal Selection
Secondary Immune Response when an individual is exposed to an antigen for a second time, the immune response is much faster (~2-7 days) the number of antibodies produced is greater & they tend to have a greater affinity for the antigen
Helper T cells play a role in both humoral & cell-mediated responses dendritic cells located in the epidermis & other tissues capture antigens and present them to helper T cells activated helper T cells can then activate both B cells & cytotoxic T cells
Active vs. Passive Immunity active immunity is conferred by: natural exposure to an infectious agent artificial exposure to an infectious agent via immunization (vaccination) passive immunity is conferred by: transferring antibodies from a person who is immune to a particular infectious agent to someone who is not examples: pregnant woman to fetus mother to nursing infant injection (artificial means)
When it all goes wrong… Malfunctions of the immune system can produce effects ranging from the minor inconvenience of some allergies to the serious and often fatal consequences of certain autoimmune and immunodeficiency diseases. Allergies are hypersensitive (exaggerated) responses to certain environmental antigens, called allergens.
Autoimmune Diseases Sometimes the immune system loses tolerance for self and turns against certain molecules of the body, causing one of many autoimmune diseases. In systemic lupus erythematosus (lupus), the immune system generates antibodies against all sorts of self molecules, including histamines. Lupus is characterized by skin rashes, fever, arthritis, and kidney dysfunction. Rheumatoid arthritis leads to damage and painful inflammation of the cartilage and bone of joints.
More Diseases… In insulin-dependent diabetes mellitus, the insulin-producing beta cells of the pancreas are the targets of autoimmune cell-mediated responses. Multiple sclerosis (MS) is the most common chronic neurological disease in developed countries, In MS, T cells reactive against myelin infiltrate the central nervous system and destroy the myelin of neurons. People with MS experience a number of serious neurological abnormalities.