Ch 43: The Immune System

Nicole FerranteBen Fewkes

Jenny Menendez

• Innate immunity:– first major kind of defense – effective from time of birth– non-specific

• Acquired (adaptive) immunity:– Second major kind of defense– Exposure after induced agents– Highly specific

Innate Immunity

• External Defense– Skin– Mucous Membrane– Secretions• Lysozyme- a secretion from skin and mucous

membranes

Innate Immunity Cont.

• Internal Defense– Phagocytosis

• Bind via surface receptors not on human blood cells• Phagocyte engulfs microbe…forming a vacuole with a lysosome• Destroyed by…

– Nitric oxide and other toxic forms of oxygen in lysosome poison microbes– Lysozyme and other enzymes degrade microbial components

Internal Defense• Phagocytic cells

– Neutrophils• Enter infected tissues, engulfing/destroying microbe• Self- destruct in phagocytosis and average life span is a few days

– Macrophages (“Big eaters”)• Large, long-lives, develop into monovytes• 5% of curculating White Blood Cells• Circulate in blood stream fcor several hours • Some migrate throughout the body others reside permanently in organs

– Eosinophils• Low phagocytic activity• Crucial to defense against multicellular parasites• Don’t engulf they discharge destructive enzymes that damage the invader

– Dendritic• Can ingest microbes• Stimulate the development of acquired immunity

• Inflammatory Response– Histamine: active chemicals in Inflammatory

Response • Trigger dilation and increase permeability of capillaries• Results in promoting blood flow to injured site

– Mast Cells• Connective tissues

– Natural Killer Cells• Patrol body and attack virus-infected cells and cancer cells

– Apoptosis: programmed cell death

Acquired Immunity

– Antigen: any foreign molecule that is specifically recognized by lymphocytes and elicits a response from them • Large molecules, either proteins or polysaccharides

– Epitope: small, accessible portion of an anitgen• Induce a response from lymphocytes

Antigen Recognition

• B Cell Receptors– “y” shaped– 4 polypeptide chains

• 2 heavy chains, 2 light chains

• T Cell Receptors: consists of 2 different polypeptide chains (α&β)– Antigen presentation: MHC molecule binds with a fragment of protein within

the cell and brings it to the cell surface– Class I MHC Molecules:

• Bind peptides derived from foreign antigens that have been synthesized in the cell• Represented in the subgroup of T cells: Cytotoxic T Cells

– Class II MHC Molecules• Dendriticcells, macrophages and Bcells known as anitgen-presenting cells• Bind peptides derived from foreign materials that have been internalized and fragmented

through phagocytosis or endocytosis

Humoral vs cell-mediated

• Humoral immune response: involves the activation and clonal selection of B cells, resulting in production of secreted antibodies that circulate in the blood and lymph

• Cell-mediated immune response: activation and clonal selection of cytotoxic T cells, which directly destroy certain target cells

T Cells

• Helper T cell: stimulates the activation of nearby B cells and cytotoxic T cells

• CD4: Helps bring the Class 2 MHC molecules with the Helper T

• CD8: Enhances interaction between a target cell and a cytotoxic T cell

Active and Passive Immunization

• Active Immunity: Depend on action of person’s own lymphcyte and the resulting memory cells specific for the invading pathogens

• Immunization/Vaccination• Passive Immunity: doesn’t depend on person’s lymphocytes

– Provides immediate protection

Blood Groups

Autoimmune Diseases

Immune system loses tolerance for self and turns against certain molecules of the body.

Example:– Systematic lupus erythematosus (lupus), generates antibodies against

the bodies natural defense (histones and DNA released by the normal breakdown.)

– Rheumatoid arthritis, damage and painful inflammation of cartilage and bone of joints.

– Insulin-dependent diabetes mellitus, insulin-producing B cells of the pancreas are targets of autoimmune cytotoxic T cell

– Multiple Sclerosis, T cells infiltrate the central nervous system and destroy the mycelin sheath that surrounds some neurons

Immunodeficiency Diseases

• Inborn (primary): result from defects in the development of various immune system cells or defects in the production of specific proteins– Severe combined immunodeficiency: both humoral and cell-mediated branches of

acquired immunity fail to function• Gene Therapy • Bone Marrow Transplants

• Acquired (secondary):an immune dysfunction that develops later in life can be caused by exposure to a number of agents. – Acquired ImmunoDeficiency Syndrome (AIDS)

• More chances for infectious diseases– HIV (Human Immunodeficiency Virus), retrovirus that causes AIDS