2DefinitionsImmunity: 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.
3HistoryDocuments 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.
4Edward Jenner noticed that milkmaids were generally immune to smallpox Edward Jenner noticed that milkmaids were generally immune to smallpox. Jenner proposed that cowpox can be used to immunize children against small pox virus (small pox vaccine). On 14 May 1796, Jenner tested his hypothesis by inoculating an eight-year-old boy by pus from cowpox blisters on the hands of a milkmaid who had caught cowpox from a cow. The boy was later challenged with small pox material and showed no sign of infection.
5nIn 1876; Robert Koch transmitted anthrax from in vitro culture to animals; he proved that the microbe is the causative agent of disease.Louis Pasteur (1881), developed the first three veterinary attenuated vaccines: chicken cholera, anthrax and rabies.In 1883, Metchnikoff observed the phagocytosis of fungal spores by leukocytes and advanced the idea that immunity was due to WBCs.
6Tissues And Organs Of The Immune System Primary lymphoid organs (development & education) Bone marrow Thymus.Secondary lymphoid organs (sites where immune cells make contact with each another) Spleen Lymph nodes Mucosal associated lymphoid tissues (MALT) e.g. tonsils.
8Barriers to infection: Human body has several barriers:Physical barriersChemical barriersBiologic barriersThese barriers provide the first line of defense against the entry of microbes.The Physical Barriers:Skin and Mucus membranesRespiratory tractUrinary tractGIT.
9Skin: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.
11The epithelium of 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.n
12The mucus trap invading microbes. Urinary Tract: The flashing action of urine (urination) washes away pathogens and prevent urinary tract infections.Respiratory Tract:The mucus trap invading microbes.The hair-like rhythmically beating cilia of the epithelia lining the respiratory tract passages remove the secretions.Alveolar macrophages play an important role in defence against microbes.GIT: intestinal peristalsis.n
14The chemical barriers: SkinGastrointestinal Tract (GIT)Respiratory Tract and Lacrimal Secretions.
15Skin: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.Several antimicrobial peptides e.g. α & β defensins which are induced by skin damage, inhibit microbial growth causing lysis.The fatty acids and sebum (lipids) have antimicrobial action.
16The 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.Respiratory tract and lacrimal secretions:In respiratory tract: β defensin and IgA has antimicrobial activity.Production of tears; which contain IgA and lysozymes (protect the eye from pathogens).
17The Biologic Barriers: Commensal Microbes (normal flora): Microorganisms that exist in a symbiotic relationship with the body. How do commensals inhibit pathogenic colonization?Production of bacteriocins (antibiotics).Competitive depletion of essential nutrients.Production of toxic products (vaginal lactic acid PH 4).Stimulation of natural antibodies.
18Examples of common commensal Bacteria Body AreaCommon CommensalStaphylococcus speciesStreptococcus (alpha hem.) Neisseria species.Bacteroides and Escherichia coli.Lactobacillus speciesSkinUpper respiratory tract, mouth, and throat.Intestinal tractGenital tract
20Establishment of Infection: Infectious diseases occur when a pathogenic organism invades human body barrier.This can be related to the following factors:The microbial virulenceThe pathogenic dose.The port of entry.The host immunity.
21nPathogenic 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.
22Ports of Entry:Ingestion.InhalationDirect penetrationExamples:Ingestion:Bacteria: Salmonella.Parasites: Entamoeba histolytica.Viruses: Hepatitis A.