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