1 / 54

HUMAN DEFENSE MECHANISMS

HUMAN DEFENSE MECHANISMS. Categories of Defense Mechanisms. Physical barriers Skin and mucous membranes Chemical factors Mechanical factors Microbiological factors Innate immunity Adaptive immunity. Physical Barriers of Defense - Skin . Stratified squamous epithelium

avonaco
Download Presentation

HUMAN DEFENSE MECHANISMS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. HUMAN DEFENSE MECHANISMS

  2. Categories of Defense Mechanisms • Physical barriers • Skin and mucous membranes • Chemical factors • Mechanical factors • Microbiological factors • Innate immunity • Adaptive immunity

  3. Physical Barriers of Defense - Skin • Stratified squamous epithelium • Chemical factors • Sebum (fatty secretion from sebaceous glands) • Lysozymes (perspiration produced by sweat glands) • Mechanical factors • Desquamation • Perspiration • Microbiological factors • Normal flora

  4. Physical Barriers of Defense – Mucous Membranes • Columnar to squamous epithelium • Chemical factors • Lysozyme in tears, saliva and nasal secretions • Enzymes and HCl in stomach secretions • Defensins in small intestine • Mechanical factors • Lacrimal apparatus • Mucociliary clearance mechanism • Microbiological factors • Normal flora

  5. Normal Flora of Skin and Mucous Membranes • Population of microorganisms that may at any time be found residing on skin and mucous membranes of human host in the absence of disease • Skin • Staphylococcus epidermidis • Propionibacterium acnes • Corynebacterium species

  6. Normal Flora of Mucous Membranes • Nasal mucosa • Staphylococcus aureus • Methicillin-susceptible (MSSA) • Methicillin-resistant (MRSA) • Nasopharyngeal mucosa • Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis • Buccal mucosa • Viridans streptococci, Neisseria species, Haemophilus species, Lactobacillus species, Prevotella species, Porphyromonas species, Fusobacterium species, Peptostreptococcus species

  7. Normal Flora of Mucous Membranes • Colon mucosa • Bacteroides fragilis group, Clostridium species, Escherichia coli and other Enterobacteriaceae, Enterococccus species, Lactobacillus species, Candida albicans • Vaginal mucosa • Lactobacillus species, Gardnerella vaginalis, Mobiluncus species, Prevotella species, Porphyromonas species

  8. PROBIOTICS • Definition • Food and Agriculture Organization of UN (FAO) and WHO • ‘live microorganisms which when administered in adequate amounts confer a health benefit on the host’ • Microorganisms • Bifidobacterium species • Lactobacillus bulgaricus • Lactobacillus casei • Streptococcus thermophilus

  9. The Innate Response to Bacterial Pathogens Complement activation via alternative pathway Phagocytosis of pathogens by Macrophages Long-lived cells Secrete cytokines in innate and adaptive immunity Function as professional APC’s Neutrophils Historically called “microphages” Enter infected tissues in high numbers Short-lived cells

  10. Activation of Tissue Macrophages • Activated macrophages initiate inflammatory response by secreting • Cytokines • Inflammatory mediators • Cytokines (chemoattractant cytokines / chemokines) • IL-1, IL-6, IL-8, IL-12 and TNF-alpha • Inflammatory mediators • Prostaglandins, leukotrienes, plasminogen activator, platelet-activating factor (PAF)

  11. Figure 8-15

  12. The Innate Response to Viral Pathogens • Virus infection of healthy cells results in production of • Interferon-alpha (IFN-alpha) • Interferon-beta (IFN-beta) • IFN-alpha and IFN-beta are type 1 interferons • Type 1 interferons • Inhibit virus replication • Activate natural killer (NK) cells • Increases expression of MHC-1 molecules

  13. Figure 8-25

  14. Natural Killer (NK) Cells • Large granular lymphocytes that circulate in blood • Functions • Killing infected cells (cytotoxic) • Secretion of cytokines • Activation by • Type 1 interferons • Infected cells • Stimulates cytotoxic function • IL-12 and TNF-alpha • Macrophages • Stimulates cytokine secretion

  15. Natural Killer Cells • Activated NK cells release IFN-gamma which activates • Macrophages • Release IL-12 • Positive feedback system for NK and macrophages • Differentiate infected from uninfected cells • NK cells express receptors for MHC class I molecules • Binding of NK cells to MHC class I molecules turn off NK cells • NK cells provide innate immunity to intracellular pathogens

  16. Adaptive Immune Response • Environment for starting provided by innate immune response • Consists of • Primary immune response • Follows initial exposure to antigen • Naive B and T cells • Establishment of memory • Secondary immune response • Follows second exposure to antigen • Memory B and T cells • Utilization of memory

  17. Primary Immune Response • Begins with T cell activation and differentiation in secondary lymphoid tissue • CD4 TH1, CD4 TH2 and CD8 • Directed by cytokines • IL-12 and IFN-gamma (TH1) • IL-4 and IL-6 (TH2) • Continues with B cell activation in secondary lymphoid tissue • Cognate interaction with CD4 TH2 specific for same Ag

  18. Role of T Cells in Primary Immune Response • Effector TH1 cells • Leave 2nd lymphoid tissue for infected tissue • Activate destruction of extracellular pathogens by macrophages • Effector CD8 cells • Leave 2nd lymphoid tissue for infected tissue • Kill infected cells • Effector TH2 cells • Remain in 2nd lymphoid tissue • Stimulates B cell differentiation into plasma cells

  19. Role of B Cells in Primary Immune Response • Differentiation into plasma cells and antibody production • Locations for differentiation following CD4 TH2 cognate interaction • Medullary chords of lymph nodes • First wave of antibody secretion • Primary lymphoid follicles • Formation of germinal centers then migration to • Medullary chords of lymph nodes • Bone marrow • Second wave of antibody secretion

  20. Secondary Immune Response • Adaptive immune response following second antigen exposure • Response is stronger and more rapid than primary • Classification • Short term (False) • 4 months or less following primary infection • Antibodies and effector T cells from naive lymphocytes • Long term (True) • 4 months or more following primary infection • Antibody and effector T cells from memory lymphocytes

  21. Secondary Immune Response • No activation of naive B and T lymphocytes with specificity for pathogen • Mechanism for naive B cells • Suppression by • Immune complex (IC) of pathogen and IgG • IC’s bind to naive B cell • Receptor • Inhibitory Fc receptor (Fc-gammaRIIB1)

  22. Clinical Application of Memory B Cell Activation • Prevention of • Hemolytic disease (anemia) of newborn • Hemolytic disease of newborn • Rh- mother with Rh+ fetus • Fetal RBC enter maternal circulation • No intervention • Maternal antibody against fetal RBC • Intervention with Anti-Rh, IgG (Rhogam) • No maternal antibody against fetal RBC

  23. Immunological Memory and a Variant Pathogen • Infection with Influenza viruses • Influenza A and B viruses mutate surface antigens • Antigenic drift (A and B) • Antigenic shift (A) • Viral strategy • Erosion of protective immunity • Strategy of immune system • Respond to strains with epitopes previously encountered • IM limited to epitopes shared by infecting and original strain

More Related