*****Read article in Scientific American and handout on Evolution of Immuity

Pathogenic substances--NON-SELF

• microorganisms, parasites, toxins, somatic mutations
• other concerns: metamorphosis, colony forming animals

Phylogentic Restriction

Race against time

Basic Mechanisms of Immunity/Defense

• recognize non-self
• mark or tag the organism
• aggregate organism
• mobilize cells to site of infection
• chemical messages: chemotaxins --- cytokines
• destroy and remove pathogen

Types of Defense Systems

• Non-specific--innate--native: generic response to foreign particles, resistance NOT improved by repeated challenge
• Specific-Immunity - adaptive- acquired
  resistance improved by repeated infection

Defense Mechanisms

• 1st line of defense---physio-mechanical barriers
• 2nd line of defense--Non-specific humoral and cellular components
• 3rd line of defense----Specific Immunity (antibodies and T-cells)

Review of phyla of animal kingdom

• invertebrates---depend on non-specific immunity as they lack specific immunity
• vertebrates--use both non-specific and specific immunity

(echinoderms questionable on antibody formation)

1st line of defense

• external body membrane
• mucous membranes
• secretions
  lysozymes ---enzyme specific for digestion of protein coat of bacteria and fungi

2nd line of defense--

Humoral

• agglutinins (lectins)-
  • -plasma proteins that cross link cell surface carbohydrates
  • sequester and opsonize particle for phagocytosis
• Complement--plasma proteins-- lysis of bacteria
• prophenoloxidase- (invertebrates)
• interferons--small anit-viral proteins

Cellular

• Phagocytic cells--
  phagocytosis-recognize, attach, ingest, digest and kill microorganism
  • invertebrates= coelomocytes, haemocytes, amoebocytes
  • vertebrates=macrophages, neutrophils
• Natural Killer cells (vertebrates)

E. Metchnikoff--Russian Zoologist observed and named phagocytes

Leukocytes--White Blood Cells (WBC)

• Neutrophils--phagocytic
• Monocytes--macrophages1*
• Eosinophils--target parasitic worms
• Basophils--release histamines

1. -antigen specific (clonal selection)
2. -systemic
3. -has "memory"

Humoral- antibody production by plasma cells (B-cells)

Cellular- T-cells (helper-T, killer-T, suppressor-T)

Lymphatic System

• found in all animals with a closed circulatory system
• blinded ended tubes with one-way flow of fluid to venous system

function-drain excess fluid from interstitium

contains water, ions, small proteins, pathogens, cellular debris

lymphocytes and macrophages

lymphatic tissue

• lymph nodes--lymph "filters", trap foreign particles, T & B-cells reside in node
• spleen
• thymus--T-cells differentiation occurs here
• aggregates of lymphatic tissue found in the gut tract and respiratory tract

compare across vertebrates--in general, as physiology became more sophisticated the lymphatic tissue became more discrete and well defined

only mammals have lymph nodes

Antibodies--

different regions bind antigen, complement and macrophages

• IgG-monomer,
• IgA-dimer, heavy chain =*
  • found in body secretions--saliva,sweat,intestinal fluid, milk
  • prevents attachment of pathogen to epithelial cell surfaces

Comparison across vertebrates

greater antibody diversity in mammals than in fish