2.2 - Innate Immunity Flashcards
Definition: pathogenesis
The ability of an organism to drive disease. Due to two factors:
- Infectivity
- Virulence
The outcome of the host-pathogen relationship is also determined by the state of the immune system
Definition: infectivity + virulence
infectivity The ability of a pathogen to establish itself on/in a host
virulence the ability to drive tissue damage
What are the groups more vulnerable to greater risk of infection
Naturally immune supressed:
- Pregnant women
- Elderly (over 65)
- Children below the age of 5
At particularly high risk due to co-morbidities
- Asplenic + hyposplenic patients (need to give vaccination against encapsulated bacteria)
- Patients with damaged or prosthetic heart valves
- Patients with previous infective endocarditis
Definition: immune system
Cells and organs (lymphoid organs, eg spleen) that contribute to immune defences against infection sand non-infectious conditions (self vs non-self)
Definition: infectious disease
When the pathogen succeeds in evading and/or overwhelming the host’s immune defences
Roles of the immune system
- pathogen recognition cell surface and soluble receptors (if cell invades cell → produces complimentary antibodies). We are all born with proteins + structures to recognise microbes that haven’t been encountered yet
- containing/eliminating the infection killing in clearance mechanisms, to try to make sure the infection doesn’t go systemic
- regulating itself so that when the infection is gone, the immune system stops → minimum damage to host (resolution). If this mechanism doesn’t work = auto-immune disease
- remembering pathogens to prevent the disease from recurring
Innate vs adaptive immunity
innate provides immediate protection
- Fast (within seconds)
- Lack of specify (so not specific to virus/bacteria etc)
- Lack of memory
- No change in intensity
- Eg skin or phagocytosis
- Death occurs with highly virulent pathogens that don’t give enough time for adaptive immunity to kick in
adaptive provides long-lasting protection
- Slow (days)
- Specificity
- Immunologic memory
- Changes in intensity (better response with repeated exposure to the pathogen)
- Eg past B-cell proliferation (B-memory cells) produce plasma cells → antibodies
What are the different elements that make up innate immunity
BARRIERS: these are the first lines of defence: factors that prevent entry + limit growth of pathogens
- Physical barriers
- Physiological barriers
- Chemical barriers
- Biological barriers
PHAGOCYTES + CHEMICALS: second line of defence
These contain + eliminate the infection
Innate immunity: physical barriers
- skin (eg eczema will increase risk of patient having cellulitis)
- mucous membranes eg mouth (candida), respiratory tract (COVID-19), GI tract (E.Coli) + urinary tract (UTIs)
- bronchial cilia (disease effecting cilia, such as cystic fibrosis, will increase risk of infection)
☞ Barrier damage can be caused by anything that is disrupting the integrity of the barrier
Eg: drugs, smoking, localised disease (eg eczema, psoriasis)
Innate immunity: physiological barriers
the point of these are to expel the microbe out of the body ☞ however, these are also used by the microbe to spread the disease further, such as diarrhoea
- Diarrhoea
- Vomiting
- Coughing
- Sneezing
Innate immunity: chemical barriers
low pH
Have this in skin, stomach and vagina
antimicrobial molecules
- IgA (antibody produced by mucosal surfaces, tears and in saliva ☞ binds to the microbe + prevents it from attaching to the cell surface, and therefore stops it entering the host)
- Lysozyme (sebum, perspiration, urine ☞ non-specific enzymes)
- Mucus (mucus membranes ☞ trap the microbes so that cilia can expel)
- Beta defensins (epithelium ☞ anti-microbial properties against microbes)
- Gastric acid + pepsin (acidic)
Innate immunity: biological barriers
normal flora
- Non pathogenic microbes (as long as they stay where they are, otherwise become pathogenic)
- Strategically located: eg nasopharynx, mouth, throat, skin, GI tract, vagina
- They are absent in the internal organs
benefits
- Compete with pathogens for attachment sites and resources
- Produce antimicrobial chemicals
- Synthesise vitamins (K, B12, other B vitamins)
- Contribute to immune maturation
What are the encapsulated bacteria
if splenectomy, at much higher risk of these
These are bacteria covered with a polysaccharide capsule eg
- Streptococcus pneumoniae
- Haemophilus influenzae
- Neisseria meningitidis
(there are others but these 3 are the most important)
Examples of normal flora that inhabit the skin, mouth and nasopharynx, and the gastrointestinal tract – these can become pathogenic if displaced from their normal location (know a couple of examples from each)
the skin
- Staphylococcus aureus
- Staphylococcus epidermis
- Streptococcus pyogenes
- Candida albicans
the mouth and nasopharynx
- Streptococcus mutans
- Streptococcus pneumoniae (encapsulated bacteria)
- Haemophilus species (EB)
- Neisseria meningitidis (EB)
the gastrointestinal tract
- E.coli
Normal flora – clinical problems start when…
normal flora is displaced from its normal location to sterile location
- By breaching the skin integrity (ie skin loss, surgery, IV lines, skin diseases, injecting drugs, tatoos)
- Faecal-oral route (ingestion, eg foodborne infection)
- Faecal-perineal-urethral route (eg urinary tract infection)
- Poor dental hygiene/dental work (dental extraction, gingivitis, brushing + flossing) as these form easy haematogenous transmission (blood-borne pathways)
normal flora overgrows + becomes pathogenic when host becomes immuno-compromised
- Eg diabetes (infection risk high due to excess glucose in blood)
- Eg AIDS, malignant diseases and chemotherapy
when normal flora in mucosal surfaces is depleted by antibiotic therapy
- Eg in intestine → severe colitis
- Eg in vagina → thrush
