Download - Introduction to Immunology:
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INTRODUCTION TO IMMUNOLOGY:
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DEFINITIONS
Immunity: resistance to disease, specifically infectious disease and tumors.
The immune system: the collection of cells, tissues, and molecules that mediate resistance to infections.
The immune response: the coordinated reaction of these cells and molecules to infectious microbes.
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HISTORY
Edward Jenner studied the immunity of the farm workers when they carried grease disease; (cowpox) from horses hooves to cow’s nipples.
Jenner proposed that cowpox can be used to immunize children against small pox virus (small pox vaccine)
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Documents show that as early as AD 1000,the Chinese custom existed of making children inhale powders made from the crusty skin lesions of patients recoveringfrom smallpox
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Anthrax was first transmitted from in vitro culture to animals by Robert Koch in 1876 ; he proved that the microbe is the causative agent of disease.
Louis Pasteur (1881), developed the first three attenuated vaccines: chicken cholera, anthrax and rabies.
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In 1883, Metchnikoff observed the
phagocytosis of fungal spores by
leukocytes and advanced the idea that
immunity was due to WBCs.
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TISSUES AND ORGANS OF THE IMMUNE SYSTEM Primary lymphoid organs
Bone marrow. Thymus.
• Secondary lymphoid organs Spleen. Lymph nodes.
• Mucosal - Associated Lymphoid Tissues (MALT)
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THYMUS & BONE MARROW
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BARRIERS TO INFECTION:
Human body has several barriers:
• Physical barriers
• Chemical barriers
• Biologic barriers
These barriers provide the first line of defense against the entry of microbes.
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THE PHYSICAL BARRIERS:
o Skin
o Mucus membranes
o Respiratory tract
o Urinary tract
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SKIN:
• The initial mechanical barrier.
-The outermost layer of epidermis (stratum corneum), is composed of dead tightly layered squamous cells. This layer is an inhospitable dry surface.
- Continuously dividing keratinocytes provides a constant detachment of squamous cells and microbes.
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Mucous Membranes:
• Mucous membranes line the body cavities.
• This epithelium contains goblet cells that secrete mucus.
• Mucus viscosity traps the inhaled microbes.
• In GIT, the mucus protects the epithelial cells and underlying tissue from damage by digestive enzyme.
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Urinary Tract:
The flashing action of sterile urine
(urination) washes away pathogens and
prevent urinary tract infections.
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Respiratory Tract:
oThe hair-like rhythmically beating cilia of the epithelia lining the respiratory tract passages remove the secretions containing trapped microbes.
o The mucus production and alveolar macrophage play an important role in defence against microbes.
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THE CHEMICAL BARRIERS:
o Skin
o Gastrointestinal Tract (GIT)
o Respiratory Tract and Lacrimal
Secretions.
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skin: • The sweat and sebaceous glands
play an important role of natural defense.
• Sweat has slightly acidic PH of 5.5 and contains lysozyme that breaks down the bacterial peptidoglycan.
• The RNAses and DNAses of skin destroy the microbial genetic material.
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• Several antimicrobial peptides e.g. defensins which are induced by skin damage, inhibit microbial growth causing lysis.
• The unsaturated fatty acids and sebum have antimicrobial action.
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The Gastrointestinal Tract:
• The highly acidic environment of stomach (pH of 1 to 3) protects the intestines.
• The secreted antimicrobial molecules (α defensine and cryptidin) of GIT destroy some pathogens.
• The digestive action of the enzymes.
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Respiratory tract and lacrimal secretions:
• In respiratory tract: β defensin has antimicrobial activity.
• Production of tears; which contain IgA and lysozymes (protect the eye from pathogens).
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The Biologic Barriers:
Commensal Microbes (normal flora):Microorganisms that exist in a symbiotic relationship with the body.
Commensals are considered as important part of natural defense because, they protect human body cavities from colonization with exogenous pathogenic organisms.
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Examples of common commensal Bacteria
Body Area
o Skin
o Upper respiratory tract, mouth, and throat.
o Intestinal tract
o Genital tract
Common Commensal
o Staphylococcus species
o Streptococcus (alpha hem.) Neisseria species.
o Bacteroides and Escherichia coli.
o Lactobacillus species
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How do commensals inhibit pathogenic colonization?
o Production of bacteriocins (antibiotics).
o Competitive depletion of essential nutrients.
o Production of toxic products (vaginal lactic acid PH 4).
o Stimulation of natural antibodies.
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Establishment of Infection: Infectious diseases occur when a pathogenic organism invades human body barrier.
This can be related to the following factors:
o The pathogenic dose.
o The microbial virulence .
o The port of entry.
o The host immunity.
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Pathogenic Dose:
It is the minimum number of organisms
required to establish an infection.
Virulence Factors :
Are microbial extracellular structures, proteins
, enzymes and toxins that enable the
microorganism to be a pathogen.
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Ports of Entry:
ingestion.
Inhalation
direct penetration
Examples:
Ingestion:
Bacteria: Salmonella.
Parasites: Entamoeba histolytica.
Viruses: Hepatitis A.
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Inhalation: Bacteria: Mycobacterium tuberculosis Fungi: Histoplasma. Viruses: influenza
Direct penetration: Trauma: Clostridum tetani. Needle stick: hepatitis B. Arthropod bite: Malaria Sexual transmission: Neisseria gonorrhoeae. Transplacental: Rubella virus. Skin penetration: Schistosoma.
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