Immunology Lecture: First Line of Host Defense 2023 PDF

Immunology (First Line of Host Defense) Prof. Ashraf M. Ahmed Department of Bacteriology, Faculty of Veterinary Medicine Kafrelsheikh University Egypt Summary of the major components of the host defenses...

Immunology (First Line of Host Defense) Prof. Ashraf M. Ahmed Department of Bacteriology, Faculty of Veterinary Medicine Kafrelsheikh University Egypt Summary of the major components of the host defenses 2  First Line of Host Defense 1. Mechanical (physical or anatomical) barriers a- Skin b- Mucous membrane 2. Chemical (physiological) barriers 3. Biological (Microbiome) 4. Genetic (heredity) barriers 3 First Line of Host Defense 4  1. Mechanical barriers a. Skin – Outermost layer – Hair follicles – Skin glands – Seat grands b. Mucous membrane 1. Digestive 2. Urogenital 3. Respiratory 4. Eye 5  a. Skin 1. UNBROKEN Skin provides a continuous layer that protects almost the whole body. Very Few Pathogens can penetrate the layers of dead cells at the skin's surface. 2. Oil and sweat glands at the surface of the skin produce a salty an acidic environment that kills many bacteria and other microorganisms. Saliva, tears and nasal secretion contain lysozome (an enzyme that destroys bacterial wall causing cell lysis).  b. Mucous Membranes Several microorganisms are capable of penetrating mucous membranes: Treponema pallidum Enteroinvasive E. coli Brucella spp. (Conjunctiva) Lacrimal apparatus: Tears make continual washing and prevent microbes from settling on the eye surface. Saliva: Washes microbes from teeth and mouth mucous memb Mucus: Thick secretion that traps many microbes. Nose Hair: Coated with mucus filter dust, pollen, and microbes. Mucociliary Escalator: Cilia on mucous membranes of lower respiratory tract move upwards towards throat at 1-3 cm/hour.  F The trachea contain cilia that entrap and propel particles out of the respiratory tract 8  b. Mucous Membranes Coughing and sneezing: Expel foreign objects. Epiglottis: Covers larynx during swallowing. Urination: Cleanses urethra. Vaginal Secretions: Remove microbes from genital tract.  2. Chemical Barriers Acidic pH of skin: High lactic acid & electrolyte concentration in sweat Sebum: Oily substance produced by sebaceous glands that forms a protective layer over skin. Contains unsaturated fatty acids which inhibit growth of certain pathogenic bacteria and fungi. Lysozymes: In Saliva, tears and nasal secretion contain Lysozymes destroys mainly Gram-positive bacterial wall causing cell lysis HCl in stomach Acidic pH of vagina: Normal flora like Lactobacillus Urine: Correlated with high concentrations of urea and ammonia. Defensins (Antimicrobials) in respiratory & GI 10  3. Biological Barriers (Microbiome) The microbiome is the collection of bacteria, viruses, fungi, and other microorganisms that live in and on human body, including the gut, skin and other mucosal surfaces with mutually beneficial coexistence. Microbiota have been linked to multiple immune functions, including the production of cytokines, maintenance of homeostasis, T cell production, and regulation of the immune system The immune system benefits from the microbiome as it provides pathogen colonization resistance. Antibiotics decrease the level and diversity of the microbiota, reducing the efficacy of the immune response 11 12  4. Genetic barriers Some hosts are genetically immune to the diseases of other hosts Some pathogens have great specificity Why? Some pathogens have a narrow host range Possible Explanations - Absence of receptor on host cell - Absence of a particular cell or tissue - Inappropriate temperature for growth - Missing nutritional requirement - Missing target for toxin Age, sex, stress, diet/malnutrition, trauma or other disease may predispose the host to infection. 13  3. Genetic barriers Examples: – Shigellosis (human not animals) – Tuberculosis (high in Negros and red Indians) – Leprosy (human not monkey) – Fungal infections 14