L1 The Nature of Host Defenses PDF

1st lecture  Important note: The lectures of immunology as part of microbiology are based on (Foundations in Microbiology –basic principles ) book authors :Kathleen Talaro and Arthur Talaro 2002 1st lecture  Lecture overview The body has a complex overlapping serie...

1st lecture  Important note: The lectures of immunology as part of microbiology are based on (Foundations in Microbiology –basic principles ) book authors :Kathleen Talaro and Arthur Talaro 2002 1st lecture  Lecture overview The body has a complex overlapping series of defenses that protect it against invasion by harmful microbes and other foreign matter. Defenses exist at several levels of development and specificity. First line defenses are inborn physical barriers such as skin, second line defenses are non-specific, protective reactions in the fluid compartments such as phagocytosis. Third line defenses are aimed at a specific pathogen and give a long-term form of protection that will come into play if that pathogen is ever encountered again. 1st lecture  acquired and specific inborn 1st lecture The multilevel, interconnecting network of host protection against microbial invasion is organized into three lines of defense. The first line consists of physical and chemical barricades provided by the skin and mucous membranes. The second line encompasses all the nonspecific cells and chemicals found in the tissues and blood includes inflammation and phagocytosis. The third line, the specific immune response, is customized to react to specific antigens of a microbial invader. This response immobilizes and destroys the invader every time it appears in the host. 1st lecture  FIRST LINE OF DEFENSE The natural, inborn, nonspecific defenses that can be divided into physical, chemical, and genetic barriers that impede the entry of microbes at the site of first contact 1st lecture  Figure 14.2 The ciliary defense of the respiratory tree. (a) The trachea and bronchi are structured to entrap and propel particles upward toward the pharynx. (b) Detail of trachea (5,000X) features tufts of cilia on the surface of epithelial cells that sweep away particles and microbes. (b): Source: Courtesy Charles P. Daghlian. http://www.dartmouth.edu/~emlab/gallery Defenses. Some nonspecific defense barriers that help prevent entry of microorganisms into the host's tissues.  Barriers at the Body’s Surface In the skin (stratum corneum) of the skin is composed of epithelial cells that have become compacted, cemented together, and impregnated with an insoluble protein, keratin. Sebaceous secretions exert an antimicrobial effect The high lactic acid and electrolyte concentrations of sweat and the skin’s acidic pH and fatty acid content Eye Blinking and (lacrimation) flush the eye’s surface with tears and rid it of irritants. Specialized glands such as the meibomian glands of the eyelids lubricate the conjunctiva with an antimicrobial secretion (lysozyme) Lysozyme: an enzyme that hydrolyzes the peptidoglycan in the cell wall of bacteria.  The Digestive Tract The mucocutaneous membranes of the free surface of digestive tract , in addition to saliva secretion (lysozyme) impedes the entry of bacteria The constant flow of saliva helps carry microbes into the harsh conditions of the stomach. - The HCl in the stomach renders protection against many pathogens that are swallowed. - the intestine’s digestive juices and bile are potentially destructive to microbes. - Vomiting and defecation also evacuate noxious substances or microorganisms from the body.  Respiratory tract effective adaptations Nasal hair traps larger particles. Flushing action and copious flow of mucus and fluids that occurs in allergy and colds. The ciliated epithelium (called the ciliary escalator) in the respiratory tree a conveys foreign particles entrapped in mucus toward the pharynx to be removed - Irritation of the nasal passage reflexly initiates a sneeze, which expels a large volume of air at high velocity. - Similarly, the acute sensitivity of the bronchi, trachea, and larynx to foreign matter triggers coughing, which ejects irritants  The genitourinary tract The mucocutaneous membranes of the free surface of genitourinary tract periodic bladder emptying and continuous trickle of urine through the ureters that flushes the urethra. Semen contains an antimicrobial chemical that inhibits bacteria the vagina has a protective acidic pH maintained by normal flora. Non Anatomical barriers like resident flora by creating an unfavorable environment for pathogens like PH in intestine and vagina Some pathogens have great specificity to infect one host species that they are incapable of infecting other species ( e.g. Humans can’t acquire distemper from cats, and cats can’t get mumps from humans) Genetic differences in susceptibility can also exist within members of one species. Humans carrying a gene or genes for sickle-cell anemia are resistant to malaria. ? Q\Why the first line does not considered a true immune response? A\because it does not involve recognition of a specific foreign substance but is very general in action. The importance of first line of defenses is manifested by examples :- 1- Patients with severe skin damage due to burns are extremely susceptible to infections 2- with blockages in the salivary glands, tear ducts, intestine, and urinary tract are also at greater risk for infection Why the first line of defense alone is not sufficient to protect against infection ? Because many pathogens find a way to circumvent the barriers by using their virulence factors.  immune terminology Immunity: the state of protection from infectious disease involving specific and non-specific elements Immunology : is the study of all biological, chemical, and physical events surrounding the function of the immune system. (to react) against infectious microbes (bacteria- viruses- fungi- parasites) and non-infectious foreign substances to eliminate them to protect the body. - The immune system: is a complex collection of fluids and cells that penetrate every organ, tissue space, fluid compartment, and vascular network of the body. - Pathogen : an infectious agent that causes disease - Infectious disease: occurs when microorganism succeeds in evading host defenses to establish a local site of infection and replication. Foreign material : Is something that can be recognized or distinguished as not being a natural part of an organism’s body Surveillance :Is the process of scouting the tissues for foreign molecules and other possibly threatening particles Recognition : Is the process of evaluating and differentiating of the molecules that detect by white blood cells surveillance. Markers : Are molecules that protrude from the cell surface like minuscule signposts announcing that cell or molecule’s identity. - Specificity: A unique configuration that dictates the kinds of immune responses it can elicit. - Receptors: Molecules that bind specifically with complementary molecules in ways that signal, communicate, and trigger reactions inside the cell. - Antigen : A foreign, non self molecule, often a surface marker, that evokes a specific immune response. Search, recognize, and destroy is the mandate of the immune system. White blood cells are equipped with a very sensitive sense of “touch.” As they sort through the tissues, they feel surface markers that help them determine what is self and what is not. When self markers are recognized, no response occurs. However, when non self is detected, a reaction to destroy it is mounted.  The immune system operates first as a surveillance system that discriminates between the host’s self identity markers and the non self identity markers of foreign cells. When it recognizes that a marker or antigen is foreign, or non self, the immune system tailors its response specifically to each different antigen. As far as the immune system is concerned, if an antigen is not self, it is foreign, does not belong, and must be destroyed. THANK YOU