• Chapter 43 – The Body’s Defenses

Vertebrate lines of defense• Innate immunity –

broad defense• Acquired Immunity –

specific defense

Innate – Phagocytic Cells• Phagocytosis: the ingestion of

invading microorgansims by certain types of white blood cells (phagocytes)

• Neutrophils: most abundant, function work inside tissues, self destruct during phagocytosis

• Macrophages: large, long lived, work inside tissues, permanently found in spleen and lymph tissue,

• Eosinophils: defense against multicellular parasitic invaders, secrete enzymes that damage invader

Innate – antimicrobial proteins • Interferons: provide defense against viral

infections• Secreted by viral infected cells which

stimulate other cells also produce interferons – shut down viral replication

• Multiple types:(α, β and γ)but not virus specific

Inflammatory response1. Tissue injury, trigger mast cells to release chemical signals

(histamine) that cause capillaries to dilate and increase permeability

2. Antimicrobial proteins and clotting elements are delivered to the injured area

3. Release chemokines (small proteins), direct migration of phagocytes to injured area

4. Phagocytes remove pathogens allowing tissue healing

Innate – NK cells• Natural Killer (NK)

cells – patrol body attacking virus-infected body cells and cancer cells

• Releases a chemical to trigger apoptosis or programmed cell death

Acquired - lymphocytes• B cells and T cells: circulate the blood and

lymph, concentrated in spleen and lymph tissue, recognize antigens with specific receptor proteins

• Both originate from pluripotent stem cells in bone marrow but T cells finish development in the thymus gland

• Antigen: any foreign molecule that is specifically recognized by a lymphocyte

Clonal Selection• Antigens bind to specific receptors,

activates a small/specific fraction of lymphocytes, will give rise to thousands of clone cells to eliminate the antigen

• Effector cells: short-lived cells that combat the antigen

• Memory cells: long-lived cells that bear receptors for the antigen

ClonalSelection

Overview of acquired immune response

• 2 branches– Humoral immune response – activation and clonal selection of B

cells, results in production of antibodies in blood and lymph– Cell mediated immune reponse – activation and clonal selection

of cytotoxic T cells, directly destroy target cells• Helper T cells: respond to nearly all antigens, when activated

secrete cytokines that stimulate lymphocytes, promote both humoral and cell mediated responses (figure 43.15)

• Cytotoxic T cells: eliminate body cells infected by viruses and other intracellular pathogens as well as cancer cells and transplanted cells (figure 43.16)

• B cells: antigen/antibody interaction to proteins and polysaccharides on the surface of cells (figure 43.17)

Helper T Cells

Cytoxic T Cells

B Cells

Classes of Antibodies• Classes of

Antibodies• Ig stands for

immuno-globulin (another name for antibody)

Antibody-Mediated Disposal of Antigens

• Phagocytosis– Viral neutralization: binding of antibodies to viral

surface proteins, blocks binding to host and increases phagocytosis

– Agglutination of antigen-bearing particles– Precipitation of soluble antigens: aggregates of body

fluid dissolved antigens• Cell Lysis

– Membrane attack complex (MAC): forms a pore in cell surface, ions and water rush in, causing cell to lyse

Antibody-Mediated Disposal of Antigens

Antibodies

Immunity – health and disease• Immunizations

– Active immunity (vaccination): depends on person’s own lymphocytes

– Passive immunity: transferring antibodies from someone who is immune to someone who is not, lasts only as long as antibodies last

Immune system problems• Allergies: exaggerated responses to antigens

called allergens; allergen binding to mast cells causes histamine releases, causes vascular system changes leading to allergy symptoms, take antihistamines to reduce symptoms

Immune system problems• Autoimmune diseases: where the body

turns on its own cells– Rheumatoid arthritis– Multiple sclerosis

• Immunodeficiency diseases: can be inborn (SCIDS) or acquired (AIDS)