Post on 24-May-2015
Chapter 43: The Immune System
By Phenix Messersmith
Evan Schwartz
Brian Shea
Mike Gaunt
Innate Immunity: Nonspecific Defense Mechanisms
• External - first line of defense: called barrier defense (ex. skin, mucous membranes, and secretions of skin and mucous membranes)
• Internal – second line of defense: phagocytic white blood cells, antimicrobial proteins, the inflammatory response
The Inflammatory Response
• Four main steps:• #1- chemical signals cause capillaries to widen • #2- fluid, other clotting elements move to site of
injury; clotting begins• #3- Chemokines released by various cells attract
more phagocytic cells to injury cite• #4- Neutrophils and macrophages engulf
pathogens and cell debris. Tissue heals.
Leukocytes
• Phagocytic white blood cells: neutrophils, macrophages, eosinophils, and dendritic cells
• Engulfs infected bacteria and infected tissue
• Discharges destructive enzymes
Acquired Immunity: Specific Defense
• Third line of defense• Examples: lymphocytes (white blood cells)
and antibodies (proteins secreted by B cells)• Able to distinguish one inducing agent from
another• Fight against antigens (foreign molecule
that elicits a specific response by a lymphocyte)
Different Types of Lymphocytes
• B Lymphocytes (B cells) – develop in bone marrow; after encountering antigens they change to antibody-secreting plasma cells (the effector cells of humoral immunity)• T Lymphocytes (T cells) – develop in the thymus;
after encountering antigens they are responsible for cell mediated immunity
More On B Cells
• Antigens bind to specific receptors and cytokines secreted from helper T cells then activate B cells
• Once activated they generate antibody-secreting effector cells or plasma cells
MHC: Major Histocompatibility Complex
• Responsible for stimulating the immune response of T cells by binding to antigens so that T cell receptors can recognize them
• Process called antigen presentation
Different Types of T Cells
• Cytotoxic T Cells- kill infected cells, cancer cells, and transplanted cells after being activated by recognizing Class I MHC molecules
• Helper T Cells- secrete cytokines that promote response of B cells and cytotoxic T cells to antigens when activated by recognizing Class II MHC molecules
The Lymphatic System
• A system of vessels and lymph nodes separate from the circulatory system that returns fluid and protein to the blood
• Stores and reproduces macrophages and other such white blood cells who fight off infections
Antibodies
• Aid in immunity by:
• 1- viral neutralization (blocks binding to host)
• 2- opsonization (increases phagocytosis)
• 3- agglutination (forms aggregates that can be readily phagocytosed by macrophages)
• 4- precipitation (of soluble antigens dissolved in body fluids)
Primary Response vs. Secondary Response
• Initial acquired immune response to an antigen which peaks about 10 to 17 upon first exposure
• When the same antigen enters the body and the response is faster, about 2 to 7 days, because there are more antibodies in the blood
Active vs. Passive Immunity
• Active: long-lasting, conferred by action of B and T cells and resulting B and T memory cells specific for pathogen
• Passive: Short-term, conferred by administration of ready made antibodies or the transfer of maternal antibodies to fetus or nursing infant
Allergies
• Hypersensitive responses to certain environmental antigens, called allergens
• Scientists believe allergies are evolutionary remnants of immune system’s response to parasitic worms
HIV: Human Immunodeficiency Virus
• Retrovirus that gains entry into the cells by using different cell types, such macrophages and brain cells, that have low levels of CD4 as receptors and co-receptors
• Main receptor for HIV is the CD4 molecule on helper T cells, this infection and loss of helper T cells allows the rise of AIDS