Human Host Defense Mechanisms Flashcards
Two types of Host defenses
Inborn (Innate) and Acquired
Characteristics of Inborn host defenses
Inborn defenses are: Natural, Non-specific and represent the first line of defense.
Characteristics of Acquired Immunity
Specific, long term and memory, T and B cell mediated. Can be active or artificial (via vaccines)
Examples of natural barriers
Skin, mucous membranes, respiratory tract, mouth, GI tract, genitourinary tract. (Combinations of mechanical barriers, chemical barriers, enzymes and flushing actions)
Characteristics of Skin
- Several outer levels of keratin (water development).
- The dermis contains tightly woven CT.
- Tough, dry, salty, oily, thick.
- Sweat glands secrete salt/fatty acid mixture (antimicrobial)
- Normal flora provides competitive inhibition to pathogens
Characteristics Mucous membranes
Bathed in antimicrobial secretions of IgG and IgA that prevent attachment
Mucociliary Escalator
Lining epithelium of mucous membranes contain cilia and mucus with IgA that propels organisms to be either sneezed or coughed. (Neutralized and eliminated out of the body)
Natural barriers of Respiratory tract
- Turbulant ariflow in nose forces particles and microbes onto mucous lining.
- Mucociliary Escalator
- Alveolar macrophages (Dust cells) can destroy pathogens that reach the alveoli.
Natural barriers in GI tract
- Acid pH of stomach
- Pancreatic enzymes, bile and intestinal secretions
- Peristalsis
- Bowel flora
Natural barriers of Genitourinary tract
- Length of male urethra
- Kidneys produce/excrete mucoproteins to bind and excrete bacteria
- Acid pH of vagina due to lactobacillus
- Constant outward flow of mucous of vagina
Natural chemical barriers
- Lysozymes in tears and saliva
- Acidic pH of skin, stomach, vagina
- Mucous secretions (IgG & IgA)
- Sebacous secretions
Function and location of: Lysozyme
Degrades peptidoglycans
Found in tears, saliva, blood and phagocytes
Function and location of: Peroxidase
Breaks down hydrogen peroxide to produce ROS. Found in saliva, body tissues and phagocytes
Function and location of: Lactoferrin
Sequesters iron from microorganisms (essential for growth).
Found in saliva, blood/tissue fluids and some phagocytes.
Function and location of: Defensins
Antimicrobial peptides inserted into microbial membrane.
Found on mucous membranes and in phagocytes.
Describe the lymphatic system
Drainage system of tissues that removes extracellular fluid or drain-off of an inflammatory response. Waste filled lymph (ECF) is shuttled through lymph capillaries to lymph vells and through lymph nodes back to the blood via the thoracic duct. Lymph always travels towards the heart.
Function of the lymphatic system
Renders surveillance, recognition and protection against foreign material.
Lymphatics and cancer
The lymphatic system carries cancer cells to other parts of the body. Called metastasis. Instead of processing and killing the cancer cells they remain in the lymph nodes and can further spread via lymphatics to other parts of the body.
Cytokines
- Bind to surface receptors on inflammatory cells.
- Induces change in cell (growth, differentiation, movement or cell death)
- Act locally, regionally or systemically
5 types of cytokines
- Interleukins
- TNF-alpha
- Chemokines
- Colony Stimulating Factors
- Interferons
Macrophages and cytokines
Pivotal cells in directing tissue inflammatory responses via their production of cytokines
IL-1 and TNF-alpha
- Produced by macrophages and develop/amplify inflammation.
- Activate endothelial cells to release more cytokines, chemokines and express adhesions of leukocytes.
- Mediate fever, catabolism of muscle and hemodynamic effects associated with inflammatory states.
Interferon-gamma
- Produced by NK and a subset of T cells.
- Potent stimulus for macrophage activation and cytokine production that helps in viral killing.
- Amplify immune response in viral and bacterial infections.
Chemokines
- Chemotactic cytokines direct cell migration of inflammatory cells to injury/infection.
2 types of chemokines
- Inflammatory chemokines
2. Homing chemokines
Inflammatory chemokines
Produced in response to bacterial toxins and inflammatory cytokines. Recruits leukocytes during host inflammatory responses.
Homing chemokines
Expressed and upregulated during disease states. Functions to direct traffic and homing of lymphocytes to lymphoid tissues during an immune response.
Colony-Stimulating Factor
Secreted glycoproteins that stimulates the production of blood cells by binding on surface of hematopoietic stem cells.
3 major Colony-stimulating factors
- CSF-1: macrophage colony-stimulating factor
- CSF-2: granulocyte macrophage colony-stimulating factor (GM-CSF)
- CSF-3: granulocyte colony-stimulating factor (G-CSF)
Gram - Sepsis and Cytokines
- LPS is a potent activator of macrophages, endothelial cells and neutrophils.
- LPS binds to a serum LPS-binding protein
- Stimulates production/release of TNF-alpha and Interleukins (1,6,8,12) which modulates endothelial cell-leukocyte adhesion, leukocyte recruitment and other immune functions.
