1Host Defense Mechanisms(non-specific)BIO162 Microbiology for Allied HealthChapter 15Page BaluchHost Defenses• Resistance– Ability to ward off disease– Varies among organisms and individuals within the same species• Immunity - mechanisms used by the body as protection against microbes and other foreign agents; self vs. non-self• Nonspecific immunity (innate, natural, inborn– Defenses against any pathogen• Specific immunity – Resistance to a specific pathogenHost Defenses2First line of defense – physical & chemical barriersFirst line of defense – physical & chemical barriers• Intact, unbroken skin (Broken skin = port of entry)• Almost all bacteria are incapable to penetrate a few helminths (hookworm & schistosoma) may• skin predominantly inhabited by Staphylococcus epidermidis• How? • Dryness• temperature• Low pH (acidic) of skin; • bacteriocidal secretion by the sebaceous glands • Desquamation – sloughing of epithelium• Perspiration (sweat contain lysozymes – attack bacterial cell wall)• Exception: Staphylococcus aureus in moist area• Eyes– Blinking of eyelids– Tears containing lysozymes• Outer ear canal– Wax contains antibacterial componentsFirst line of defense – physical & chemical barriers3• Mucus membranes – layers of mucosal cells that line body cavities that open to the outside (digestive, genitourinary and respiratory tracts)– Mucus is produced by the mucosal cells• Contains antimicrobial substance such as lysozymes, lactoferrin (sequester iron) • Mucosal cells are rapidly dividing  flush out of body along with attached bacteriaFirst line of defense – physical & chemical barriers• Digestive tract– Mouth and lower digestive tract – lots of bacteria (mostly anaerobes e.g. Bacteroides, anaerobic streptococci [Streptococcus mutans in mouth] and Clostridium in colon )– How?• Mucus• Saliva (contains lysozyme)• Bile (alkaline) in small intestine• Stomach acids• Defecation (feces contains up to 50% bacteria !)• Mucus contain antibacterial agents, antibodies and immune cells called phagocytesFirst line of defense – physical & chemical barriers• Genitourinary tract– Urinary tract is sterile in a health person except the distal urethra – How?• Urination• Secretion (vaginal and seminal fluid)• Low pH of vagina (presence of several Lactobacillus sp., Candida albicans)First line of defense – physical & chemical barriers4First line of defense – physical & chemical barriers• Respiratory tract– Nose - nasal hair, mucus secretions (phagocytes and antibacterial enzymes), irregular chambers – ciliated epithelium (nasal cavity, sinuses, bronchi and trachea)– Cough reflexes– Alveolar macrophages • Microbial antagonism– Normal flora vs. invaders• Compete for colonization sites• Compete for nutrients• Produce bacteriocins– Administration of broad spectrum antibiotics may kill only certain members of the normal flora, leaving the others to overgrow  superinfectione.g. yeast in vagina – yeast vaginitisClostridium difficile in colon – diarrhea and colitisFirst line of defense – physical & chemical barriersSecond line of defense• Once beyond the protective outer barrier of the body, the invading microbes will encounter a series of nonspecific cellular and chemical defense mechanisms• Mechanisms:– Inflammation – a series of events that removes or contain the offending agent and repair the damage– Chemotaxis – movement of cells toward a chemical influence (chemokines or chemotatic agents)– Phagocytosis – process in which cell ingest foreign particulate matter e.g. microbes• Many are carried out by the white blood cells in blood5Blood Components• Fluid portion– Serum: liquid portion of clotted blood– Plasma: liquid portion with clotting factors– “Plasma can clot; Serum cannot”– Contains antibodies & other proteins• Clotting factors (proteins)– Fibrinogen– Prothrombin• Formed elements– Erythrocytes – red blood cells (RBC) – carry oxygen and carbon dioxide; no nucleus– Leukocytes – white blood cells (WBC) - defense– Platelets – thrombocyte particles – clotting; no nucleusMonocytes(marcophage)LymphocytesNeutrophilsEosinophilsBasophilsErthrocytes(RBC)PlateletsSecond line of defense – formed element in bloodWright’s stain of the peripheral blood cells can identify granulocytes based on properties of the granules. It contain two dyes:• Eosin dye stains basic cell components  reddish• Methylene blue dye stain acidic cell components  blue-ishFormed Elements In Blood6Formed Elements In BloodWandering or Fixed Can you identify these leukocytes?erythrocyteplateletGranulocytesNeutrophils (aka polymorphonuclear cells or PMN)• Most common leukocytes in the blood. Granules unstained.• mobile cells and can pass through capillaries and engulf bacteria by phagocytosis• secrete a fever inducing agent called pyrogenwhich also helps the body fight infection. Eosinophils• the granules of cytoplasm are stainable with eosin (red) • The exact function of eosinophils has been a mystery for many years, but research has pointed to its role in allergy, asthma and parasitic (helminth) infection; some phagocytosis. Basophils• rarest WBC in normal blood• Blue granules contain histamine• play a role in immediate hypersensitivity reactions and in some cell-mediated delayed reactions, such as contact hypersensitivity in humans, skin graft or tumor rejections7Monocyte (Macrophage)Monocytes (the blood form) • the largest WBC's normally found in blood • horseshoe or "U" shape nucleus, or it may be folded• travel to different tissue to mature into specific macrophageMacrophage• As it developed from monocytes, its size can increase 2-3 times• Wandering – motile and travel in bloodstream; found throughout body• Fixed (histiocytes)– attached and remain in the tissue• Removal and engulfment of foreign particles and useless body cells/materialLymphocytes• The lymphocyte nucleus is usually round to slightly indented with a sharply defined edge, and deep, dense purple. Cytoplasm may be scant or form a narrow rim around the nucleus.• Cornerstone of the immune system: antibodies production & cell-mediated immunitySecond line of defense• Acute phase proteins– set of plasma proteins whose level increases during infection to enhance host defense mechanisms – e.g. complement proteins, coagulating