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IMMUNE SYSTEM AND BODY'S DEFENSE (Adaptive Defenses of the T…
IMMUNE SYSTEM AND BODY'S DEFENSE
Innate Defenses
Surface barriers
First line of defense
Mucous membranes
Cilia
Propel debris-laden mucus away frtom nasal cavity and lower respiratory passages
Fast; non-specific
Acid mantle of vagina
Inhibits growth of most bacteria and fungi in female reproductive tract
Mast Cells
Release granules that contain histamines which increases vasodilation and capillary permeability
Intact skin
Forms mechanical barrier that prevents entry of pathogens and other harmful substances in the body
Nasal Hairs
Filter and trap microorganisms
Urine
Normally acid pH inhibits bacterial growth; cleanses the lower urinary tract as it flushes from the body
Keratin
Provides resistance against acids, alkalis, and bacterial enzymes
Lacrimal secretion; tears, saliva
Continuously lubricate and cleanse eyes and oral cavity
Lysozyme, an enzyme that destroys microorganisms
Adaptive Defenses of the T-Lymphocytes
Cell-Mediated Immune Response
Stimulus for clonal selection and differentiation of T cells is binding of antigen
T cells must accomplish a double recognition process:
They must recognize self (MHC protein) and nonself (antigen) at the same time
T cell activation
A T cell antigen receptor bind to antigen-MHC complex on the surface of a cell body
T cell must recognize one or more proliferates to form a clone of cells that differentiate and perform functions according to their T cell class
T cell Roles
Helper T cells stimulate proliferation of other T cells and B cells that have already become bound to antigen
Cytotoxic T cells are the only T cells that can directly attack and kill other cells displaying antigen to which they have been sensitized
Regulatory T cells release cytokines that suppress the activity of both B cells and other types of T cells
Gamma delta T cells are found in the intestine and are more similar to NK cells than other T cells
Without helper T cells there is no adaptive immune response because the helper T cells direct or help complete the activation of all other immune cells
Pathway
Self cells or APCs displaying foreign antigens bind to T cells
Interleukins costimulate activation of T cell
If MHC-I and endogenous antigens are displayed on the plasma membrane, T cells proliferate, producing cytotoxic T cells. Cytotoxic T cells destroy cells displaying the antigens
If MHC-II and exogenous antigens are displayed on the plasma membrane, T cells proliferate, producing helper T cells. Helper T cells release interleukins (and other cytokines), which stimulate B cells to produce antibodies that bind to the antigens and stimulate nonspecific agents to destroy the antigens
Third line of defense
Specific but slower
Adaptive Defenses of the B-Lymphocytes
Humoral Response
Activated when antigens bind to its surface receptors
Clonal selection is the process of the B cell growing and multiplying to form an army of cells that are capable of recognizing the same antigen
Plasma cells are the antibody-secreting cells of the humoral response; most clonses develop into plasma cells
Clones that do not become plasma cells develop into memory cells
B-lymphocytes
Made in bone marrow
Matures in bone marrow
Passive Humoral Immunity
Occurs when a person is given preformed antibodies
Vaccines
Active Humoral Immunity
Occurs when the body mounts an immune response to an antigen
Infected body cells
Immunological Memory
Primary immune response occurs on first exposure to a particular antigen with a lag time of 3-6 days
Secondary immune response occurs when someone is re-exposed to the same antigen. It is faster, more prolonged, and more effective
Pathway
B-cells recognize antigens or pathogens that are circulating in the lymph or blood
Antigens bind to B cells
Interleukins or helpter T cells costimulate B cells. Antigen and a costimulator are required to activate a B cell and initiate B cell profileration.
B cells proliferate and produce plasma cells. The plasma cells bear antibodies with identical antigen specificity as the antigen receptors of the activated B cells. The antibodies are released and circulate through the body, binding to antigens.
B cells produce memory cells. Memory cells provide future immunity.
Specific but slower
Cellular innate defenses
Second line of D-defense
Phagocytes
White blood cells
Macrophages
Derive from Monocytes that leave the blood stream and enter the tissues and develop into macrophages
"Big Eaters"
"Clean up crew that stays longer"
Eosinophils
Targets parasites
Degranulate and release enzymes and other substances that are lethal to the parasite
Heavy artillery that "takes on the big guy"
Neutraphils
Most abundent
First to arrive at site of infection
"Foot Soldiers"
Pierce the pathogen's membrane by using defensins
Basophils
Reside in the blood
Increase fluid movement. Release histamines which increases vasodilation and capillary permeability
"Engage in chemical warfare"
Natural Killer (NK) Cells
"Police" the body in blood and lymph
Lyse and kill cancer cells and virus-infected body cells
and serves as security gaurd that seeks and destroys
Mature in lymphoid tissue
Engulf pathogens by phagocytosis
Engulf and destroy pathogens that breach surface membrane barriers
Tissue Injury
Inflammatory response
Release o f inflammatory chemicals
Histamine
Granules of mast cells and basophils.
Promotes vasodilation of local arterioles. Increases permeability of local capillaries, promoting formation of exudate
Kinins
Plasma protein
Same as for histamine. Also induces chemotaxis of leukocytes and prompt neutrophils to release lysosomal enzymes
Prostaglandins
Fatty acid molecules produced from arachidonic acid found in all cell membranes
Same as for histamine. Also induce neutrophil chemotaxis. Induce pain.
Complement
A group of bloodborne proteins that, when activated, lyse microorganisms, enhance phagocytosis by opsonization, and intensify inflammatory and other immune responses
Cytokines
Iterferons
Proteins released by virus-infected cells and certain lymphocytes; act as chemical messangers to protect uninfected tissue cells from viral takeover; mobilize immune system
Promote apoptosis by directly attacking virus-infected or cancerous body cells; recognize general abnormalities rather than specific antigens; do not form memory cells
Leukocytosis
Margination
Diapadesis
Chemotaxis