Immune System

System of chemicals, white blood cells, and tissues that protect the body against pathogens (disease causing microorganisms) Immune system has non-specific and specific responses Aided by lymphatic system

Lymphatic System Returns fluids leaked from the blood back to the blood Contains many different types of leukocytes involved in the immune response Lymphoid organs include: lymph nodes, spleen, thymus, tonsils, and lymphoid tissue in digestive and respiratory tracts Lymph nodes filter lymph of pathogens and activates immune response against an antigen

Lymph Node

White blood cells originate from stem cells in red bone marrow

Lines of Defense Against Pathogens Nonspecific system: 1st line of defense (surface membrane barriers): - skin (keratin) and acid mantle (sweat, sebum) - mucous membranes and secretions (saliva, tears, mucus, stomach acid, enzymes, urine, earwax, nasal hairs, etc.) 2nd line of defense (cell and chemical defense): -Phagocytes: white blood cells that “eat” foreign matter (ex. Macrophages, dendritic cells) -Natural killer cells (kill virus infected cells) -chemicals released from cells and damaged tissues (interferon, histamine, complement) -Inflammation (attracts white blood cells to the area and prevents spread of infection) and fever (speeds up the activity of white blood cells and slows down viral replication)

Specific (Adaptive) System (3 rd line of defense) React against a specific antigen (cell membrane protein) on the surface of the pathogen. Involves B-lymphocytes (humoral immunity) and T-lymphocytes (cell-mediated immunity) Also involves antigen-presenting cells (APC) like macrophages and dendritic cells (ingest pathogen and display the pathogen’s antigens on their surfaces)

B-lymphocytes (B-cells) Type of lymphocyte involved in humoral immunity Develop into plasma cells which secrete antibodies when they recognize an antigen Antibodies are made against specific antigens Memory B cells are produced after 1st exposure to antigen - results in quicker response if the person is exposed to the same antigen again Antibody binding to antigen

Primary and Secondary Immune Response Blood antibody level rises more quickly with 2nd exposure Memory cells formed

T cells Type of lymphocyte involved in cell-mediated immunity Cytotoxic T-cells (T c ) kill only cells that are infected with a virus Helper T-cells (T h ) release chemicals called cytokines to activate B-cells, cytotoxic T-cells, and macrophages Suppressor T-cells (T S ) slow down activity of B and T cells once the antigen has been destroyed Memory T-cells cause quicker response if infection with same pathogen occurs again Helper T cell signaling B cell to differentiate into plasma cell and produce antibodies

MHC Proteins Proteins on the surface of cells that identify a cell as belonging to the organism Class I MHC are found on all body cells Class II MHC are found only on certain cells that are part of the immune response MHC proteins are used to display foreign antigens for recognition by T and B lymphocytes

Hypersensitivity (allergies) When the immune system overresponds to a harmless antigen causing tissue damage in the process Antigen stimulates overproduction of IgE antibodies by B cells (plasma cells) IgE antibodies attach to mast cells which contain histamine Histamine is released in mass quantities when a second exposure to the antigen occurs Histamine causes the symptoms of allergies Animation #4

Active vs. Passive Immunity Active - a person’s immune system forms memory cells against an antigen (either through contracting an illness or through a vaccine) Passive - a person receives antibodies against an antigen but does not form memory cells

Tissue and Organ Transplants MHC antigens (HLA antigens) are compared to determine a match between donor and recipient Must be at least 6 MHC antigens in common in order to consider a transplant Immunosuppressant drugs must be given to prevent a rejection Each day, about 77 people get the organ transplant that gives them a second chance, but 19 others die waiting for a donated organ.

Inflammation and CV disease Some interleukins are released by macrophages and endothelial arterial cells IL-6 attracts white blood cells to eat cholesterol deposited by LDL and burst forming plaque