Innate and Acquired Immunity

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					Lecture 3

Innate and Acquired Immunity

• Distinction between innate and specific immunity
• Discuss mechanisms of innate immunity
– Barriers – Recognition of invading microorganisms – Phagocytosis

– Inflammation

Innate Immunity

Specific Immunity

Innate Immunity
• Refers to various PHYSICAL, CHEMICAL, and CELLULAR attributes that collectively represent the first line of defense against infectious disease.

Innate Immunity
• Natural Immunity

• Phylogenetically older: Present in all Multicellular Organisms
• Use Proteins Encoded in the Germline (Elements an Individual is born with: Standard EquipmentHard-Wired

Innate Immunity Features
• Preformed: Rapid-Available on Short Notice • No Memory:Not Enhanced by Prior Exposure:

• Broad Specificity
• Dependent on species, strain, sex.

Acquired/Specific Immunity
• Acquired Following Exposure to the Microorganism.

Acquired/Adaptive/Specific Immunity Features
• Specificity

• Memory
• Specialization • Self/Nonself recognition

Innate vs. Acquired Immunity
• Innate/Natural/ Nonspecific – present from birth – operates against any substance – not enhanced by prior exposure • Acquired/Adaptive/Sp ecific – defense mechanisms tailored to individual pathogens – enhanced by prior exposure

Mechanisms/Components of Innate Immunity

• Anatomic barriers • Physiologic barriers • Phagocytic/Cellular Barriers • Inflammatory Barriers

Anatomic Barriers
• External/First line of defenses • Epithelial Barrier
– Skin – Mucous membranes

–Conjunctivae, GI, resp, urogenital tracts

–secretions (saliva, tears, urine, mucus)
–wash/trap/inhibit growth –cilia

Functions of Epithelial Barrier


Physiological Barriers
• Temperature-Fever • pH-Stomach, vagina, and skin

• Normal microflora of GI tract, skin Superinfection
• Chemical Mediators
– Defensins-Secreted by Epithelia
– Hydrolytic enzymes of Saliva – Lysozyme in tears

Physiological Barriers (Contd.)
– Interferons-viral infection


Cellular Barriers

• Following Penetration of Anatomical and Physiological Barriers

• Specialized Cells : Function is to Destroy Invader

Innate Immune Recognition Microbial Nonself Macrophages Missing Self Natural Killer Cells

Recognition of Microbial Nonself
• Depends on recognition of “Pathogen Associated Molecular Patterns (PAMPS)” – Gene products unique to microbes-Molecular Signatures of microbial invaders – Conserved among microbes of a given classInvariant – Essential for microbial survival – LPS (Gram negative bacteria); Peptidoglycan (Gram positive bacteria)

Pattern Recognition Receptors (PRRs)
• Recognize PAMPs • Receptors expressed on macrophages • Signal to induce inflammatory cytokines and activate host defense mechanisms Examples:

Macrophage mannose receptor Macrophage Scavenging Receptor-LPS and Gram neg. bacteria Toll-like Receptors

Receptors of The Innate Immune System


Receptors and Responses of Phagocytes in Innate Immunity


• Eating by Cells • Ingestion/Engulfment and Destruction of Invading Foreign Particles such as Bacteria • 1883: Metchnikoff

Professional Phagocytes

• Neutrophils
• Macrophages

Phagocytosis of Bacteria by Macrophages

• Adherence and Opsonization

• Ingestion
• Destruction

Opsonins and Opsonization

Adherence and Opsonization
• Adherence to Surface Receptors
– Mannose Receptor – Scavenger Receptor

• Opsonins: Greek- “Prepare food for”
– Enhance Phagocytosis – Antibodies-Fc Receptors

– Complement Proteins-Complement Receptors

QuickTime™ and a Cinepak decompressor are needed to see this picture.

Resistant Pathogens
• Brucella abortus

• Listeria monocytogenes-Escape into the cytoplasm • Mycobacterium avium, tuberculosis-cell wall lipid prevents phagolysosome formation • Salmonella typhimurium • Candida albicans

Evasion of Innate Immunity by Microbes

• Infection

• Injury
• Irritants

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