chapter 43: the immune system. lymphocytes: specialized white blood cells : two types: b lymphocytes...
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Chapter 43:The Immune System
Lymphocytes:
Specialized White Blood Cells:
Two Types:B LymphocytesT Lymphocytes
Lymphocytes:
B cells:
Formed and mature in red bone marrow
Named for Bursa of Fabrica (birds)
T Cells
Formed in red bone marrow
Mature in Thymus
Lymphocyte Action:
Primary lymphatic organs:Red bone marrow
Thymus
Secondary lymphatic organs:Lymph tissue, nodule and nodes
Spleen
Tonsils
Interacts with APC, antigens and other lymphocytes
Lymphocyte Activation:
1. Antigen recognitionEpitope- antigenic determination
Specific sites on the antigen that is recognized by lymphocyteMany different determinants on each antigen
2. Proliferation and destruction
Antigen Receptors:
B cell receptorsY shape
2 heavy chains
2 light chains
Disulfide linkages
Anchored to cell
Variable region acts as specific antigen binding site
T cell receptors
Two chainsα- chain
β- chain
Disulfide linkages
Anchored to cell
Variable region acts as specific antigen binding site
Major Histocompatibility Complex: MHC
MHC complexes present antigen particles to the surface of the host cell
Necessary for immune response
Two Types Of MHC:
MHC IFound on all nucleated cellsWill display to cytotoxic T cells
MHC IIFound on all APC’s, including:
B- cellsMacrophagesDendritic cells
Will display to helper T cells
Cytotoxic T cells: • Cell Mediated Immune Response• Viruses, Cancer and other
intracellular pathogens• Associated with MHC I• CD8 surface protein• Enhances interaction between cytotoxic
T cell and APC
• Activation is stimulated by cytokines from helper T cells
Cytotoxic T Cells:Once Activated cytotoxic T cells release:
Perforins- create pores in the cell membrane of the host cellUse proteolytic enzymes to initiate apoptosis
Helper T Cells:Cell Mediated and Humoral Immune Response
Activated by:APC
Cytokine released by macrophage
Associated MHC II
CD4 surface proteins-enhance interaction between helper T cell and APC
Releases cytokines:Interferons
interleukins
Cytokine Action:Interferons:
Prevent viral replication
Activates macrophages and NK cells
Secreted by virus infected cells, fibroblasts, macrophages and B cells
Interleukins:
Costimulation of T and B cells
Prostaglandin production
Inflammatory response
Activates macrophages and NK cells
Produces eosinophils
Secreted by B cells, macrophages and fibroblasts
Clonal Selection:Antigen binding to receptor
Lymphocyte proliferation forming clones of identical cells
Cells bearing same receptors
Differentiation: Effector cells- fight off primary infectionMemory cells- rapid response upon secondary exposure of same antigen
Induction of Immune Response
Primary immune response
Selective proliferation and differentiation of lymphocytes from first exposure
10- 17 day peak response time
Secondary immune response
Fast response time to secondary exposure of same antigen
2-7 days peak response time.
Types of Immune Response:
Humoral Immunity
B cell activation
Production of antibodies
Defense against bacteria free in the lymph and blood plasma, incompatible tissues, pollen and bee venom (extracellular pathogens)
Cell- Mediated Immunity
T cell activation
Binds to and/or lyses cells
Defend against intracellular pathogens, including; viruses, bacteria, fungi, protozoa, parasites and cancer cells
Antibody Structure and
Function: Epitope: region on antigen surface recognized by antibodies
2 heavy chains and 2 light chains joined by disulfide bridges
Antigen-binding site (variable region)
Structure of an antibody:
5 classes of Immunoglobins
IgM: 1st to circulate; indicates infection; too large to cross placenta
IgG: most abundant; crosses walls of blood vessels and placenta; protects against bacteria, viruses, & toxins; activates complement
IgA: produced by cells in mucous membranes; prevent attachment of viruses/bacteria to epithelial surfaces; also found in saliva, tears, and perspiration
IgD: do not activate complement and cannot cross placenta; found on surfaces of B cells; probably help differentiation of B cells into plasma and memory cells
IgE: very large; small quantity; releases histamines-allergic reaction
Antibody- mediated Antigen Disposal:
Opsonization: antibody binds to and blocks antigen activity-coats antigen surface enhancing macrophage activity
Agglutination: antigen clumping- antibodies contain at least two antigen binding sites
Precipitation: cross-linking of soluble antigens- forms immobile aggregates that are disposed of by phagocytosis
Viral Neutralization: antibodies bind to certain proteins on the surface of a virus blocking its ability to infect a host cell
Immunity in Health & DiseaseActive immunity
Depends on persons own lymphocytes
natural: conferred immunity by recovering from disease
artificial: immunization and vaccination; produces a primary response
Passive immunity
transfer of immunity from one individual to another
natural: mother to fetus; breast milk
artificial: rabies
Transfer of antibodies from rabid(immune) animal to non-rabid (non-immune) animal
Blood Groups:
Why is blood type AB the universal recipient and blood type O the universal donar?
Tissue and Organ Transplant
MHC’s responsible for rejection of tissue and organ transplant
No two individuals have exact same MHC’sExceptions???How do doctors compensate for this???
Abnormal Immune Function:
Allergies (anaphylactic shock): hypersensitive responses to environmental antigens (allergens); causes dilation and blood vessel permeability
Allergy symptoms can be diminished with antihistamines
The hormone epinephrine counter acts this allergic reaction
Self/Nonself Recognition:
Self-tolerance: capacity to distinguish self from non-self
Autoimmune diseases: failure of self-tolerance; multiple sclerosis, lupus, rheumatoid arthritis, insulin-dependent diabetes mellitus
Immune Deficiencies:
Inborn (primary):• defects in the development of various
immune system cells and or proteins• SCID- severe combined
immunodeficiency
No cell-mediated immune response
Requires bone marrow transplant
Acquired (secondary)AIDS: Acquired Immunodeficiency Syndrome
HIV virus (Human Immunodeficiency Virus)
Retrovirus
Uses CD4 receptor to enter cell
Causes loss of helper T cells