Priscilla Johanesen; Week 7 MED1011; Microbiology
Innate defences are antigen non-specific, adaptive is antigen specific. Innate immunity is broad spectrum, responses occur immediately or over several hours, no memory or lasting protective immunity, limited repertoire of recognition molecules, responses are phylogenically ancient. Anatomical barriers are skin (physical barrier), mucous membranes (line body cavities open to the exterior). Mechanical barriers are cilia and mucus, coughing and sneezing, vomiting and diarrhoea, physical flushing. Antimicrobial/chemical factors are fatty acids on skin, gastric acids and pepsin, lysosyme, anti-microbial substances which directly destroy microorganism such as cryptidins and defensins, cytokines and chemokines, complement (circulate in proenzyme state, activated by a variety of mechanisms, 3 pathways: classical, alternative and lectin).
Classical pathway is antigen/antibody complexes on pathogen surfaces, MB-lectin pathway binds mannose on pathogen surfaces, alternative pathway is on pathogen surfaces. Targets them for destruction by phagocytes, creates donut pores called membrane attack complexes.
Innate immune has cellular components such as WBC which have phagocytic cells, cells that release inflammatory mediators, NK cells. Macrophages engulf pathogens and circulate in blood/lymph/ECF, neutrophils are most abundant WBC and ingest microorganisms and destroy them creating pus. NK cells attach and kill host cells that have been invaded, as well as potential cancer cells.
Inflammation is indicated by redness, heat, swelling, pain, loss of function, is a non-specific response. Provides early protection by restricting tissue damage to the site of infection. Occurs when pro-inflammatory enzymes signal to endothelial cells to make them leaky to fluid and sticky for WBC. Can also be triggered by complement or coagulation system. Fever often accompanies inflammation, is natural reaction to a number of illnesses. Is body temperature above 37 degrees, associated with sweating, hypertension and vasodilation. Allows faster recovery.
Normal flora lives on tissues without causing harm, can be resident flora or transient. Normal flora is very complex, each person has their own individual flora which changes continously throughout life. More microorganisms are present than human cells at any one time. Normal flora prevents colonisation (skin takes up space and nutrients, produces fatty acids) (gut ferments unused energy substrates, produces bacteriocins and colicins, synthesises and secretes vitamins, trains the immune system) (vaginal lactobacilli secrete acid).
Host-parasite relationship can be symbiotic; mutualism is two organisms living together for mutual benefit such as E coli in the colon which produces K and some B and breaks down waste; commenalism is where one benefits and other is not harmed; parasitism is where one benefits and other is harmed. Normal flora are only parasitic where they cause infection. Chronic carriers of microorganisms can have multiplication and shedding at low levels, absence of symptoms, capable of transmitting infection.