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Immunology Flashcards

1
Q

Describe the processes behing bacterial pyoderma

A
  • Staphylococcus intermedia most common
  • Can be superficial (epidermis and hair follicles) or deep (dermis/deep dermis)
  • Pus in skin
  • Bacterial cause
  • Pustules not always obvious
  • Neutrophils lead to pyogenic efect
  • Cytokines recruit neutrophils, engulf bacteria end up with chronic disease
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2
Q

Describe the lymph of the skin

A
  • Afferent lymph deep to epidermis
  • Gives rise to cells surveying tissue e.g. T lymphocytes and toehr dendritic cells
  • Allows mobile populations of cells as well as static
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3
Q

Where are mast cells located?

A

At all points of interface with environment

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4
Q

Describe the actions of Langerhans cells

A
  • Epidermis
  • Phagocytose pathogens
  • Act as exceptional APCs
  • Precursors of dermal dendritic cells
  • Migrate into dermis during maturation, become dermal dendritic cell
  • Make was as APC to initiate and maintain immune responses
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5
Q

Describe macrophages of the dermis

A
  • Phagocytose and kill pathogens

- Good APCs

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6
Q

What are the different types of hypersensitivity reactions?

A
  • Type I: immediate, IgE
  • Type II: IgG
  • Type III: IgG/immune complex
  • Type IV: T cell
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7
Q

Describe Type I hypersensitivity

A
  • Immediate (30 mins)
  • Mast cel degranulation
  • IgE mediated
  • IgE bound to receptors on mast cells and basophils (Fc Epsilon RI)
  • Degranulation via antigen contact with antigen specific IgE on mast cell/basophil
  • Leukocyte stimulation/migration
  • Esp. eosinophils
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8
Q

Give examples of type I hypersensitivity

A
  • Allergy

- Asthma

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9
Q

Describe type II hypersensitivity

A
  • IgG mediated
  • Antibody-dependent cell mediated cytotoxicity
  • 5-10h
  • Ab recognises self antigen on host cell or tissue
  • Or recognises small molecule bound to cell or tissue
  • Cell opsonised and phagocytosed by innate immune cells
  • Or innate immune cells engage antibody produced cell toxins e.g. NK cell killing
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10
Q

Describe an example of type II hypersensitivity

A
  • Pemphigus vulgaris
  • Dogs and cats most common
  • Phagocytes destroy epithelium = epidermal lesions
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11
Q

Describe type III hypersensitivity

A
  • Immune complexes, soluble antigen, deposits on vessel wals (e.g. joints, kidney) = inflammatory reaction and destruction of tissue
  • Complexes escape normal clearance
  • Antigen solube, not attached to organ involved
  • May be from exogenous source e.g pathogen
  • Or endogenous
  • Complexes deposit in tissue to allow receptors on mast cells to bind
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12
Q

Give an example of a localised Type III reaction

A
  • Arthus reaction

- Vasculitis in skin e.g. to injected antigen

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13
Q

Describe tissue destruction in type II hypersentitivity

A
  • Bound to tissue
  • Mast cell binds to antigen
  • Leads to degranulation
  • Vasodilation
  • Increased recruitment of neutrophils
  • Leads to tissue destruction
  • e.g. Discoid lupus (chronic skin condition)
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14
Q

Describe type IV hypersensitivity

A
  • T cell mediated
  • Delayed (24-72h)
  • Dendritic and primed T cells
  • T cells recruit and activate mononuclear cells e.g. monocytes and tissue macrophages
  • Inflammation at site of DC/T cell interaction occurs not at draining lymph node
  • Accumulation of T cells and bacteria
  • Granuloma formation
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15
Q

What are the 3 claassifications of type IV hypersensitivity?

A
  • Contact
  • Tuberculin
  • Granuloma
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16
Q

Describe contact type IV hypersensitivity

A
  • Reaction time 48-72h
  • Eczema appearance
  • Lymphocytes followed by macrophages
  • Oedema of epidermis
  • Antigen site is epidermis
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17
Q

Describe tuberculin type IV hypersensitivity

A
  • Reaction time 48-72h
  • Local induration appearance
  • Lymphocytes, monocytes, macrophages
  • Intradermal antigen site
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18
Q

Describe granuloma type IV hypersensitivity

A
  • Reaction time 21-28 days
  • Hardened appearance
  • Macrophages, epitheloid and giant cells, fibrosis
  • Persistent antigen or foreign body presence
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19
Q

Compare primary and secondary skin infection

A
  • Primary: pathogen is direct cause
  • Secondary: infection results from underlying disease e.g. allergic disease leading pruritus and thus skin damage through which infection can occur
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20
Q

Give examples of immune medaited skin diseases

A
  • Flea allergy dermatitis (FAD) and Atopic dermatitis (AD)

- Pemphigus, discoid lupus-

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21
Q

Describe pemphigus

A
  • Blistering autoimmune disease
  • Auto-antibodies to desmoglein
  • Antibodies unglue cells (acantholysis), leading to bliserting
  • Treated with oral steroids
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22
Q

Describe discoid lupus erythematosus

A
  • Mainly chronic skin condition
  • Inflamed skin patches
  • Scaling and crusty
  • Lighter centre area
  • Autoimmune disease - antibodies attacking healthy cells
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23
Q

How is type IV hypersensitivity used in TB testing?

A
  • Single intradermal comparatice cervical tuberculin test
  • If positive will react to injection of M bovis antigen as T cells already primed
  • Measure skin thickness to establish granuloma formation
  • Indicates previous infection
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24
Q

What are atopic dermatitis and flea allergic dermaititis examples of?

A
  • Type I allergic reactions

- Immune mediated, with IgE hypersensitivity

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25
Q

Describe flea allergic dermatitis

A
  • Pruritic condition of dogs and cats
  • Most common skin disease
  • Reaction to flea saliva peptides
  • Produce histamines in response
  • Erythema, papules, pustule, crusts
  • Sensitised animals intermittently exposed to fleas have increased reaction
  • Lessened reaction if constantly exposed
  • Mainy Type I, many also show type IV
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26
Q

Describe type I hypersensitivity in FAD

A
  • Mast cells and IgE in skin
  • Migration of eosinophils into skin
  • Basophils sensitive to allergens in flea saliva
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27
Q

Describe atopic dermatitis

A
  • Pruritic skin disease
  • Cause often undiagnosed
  • IgE
  • Atopy is genetic tendency to develop allergic disease
  • WHWT and boston terries more susceptible
  • Occurs when in contact with allergen e.g. house dust mite, capet fibres etc
  • Th2 response: cytokines, eosinophils and mast cells etc in tissue
  • Th1 cytokines in chronic lesions
  • Tolerance associated with anti-inflammatory cytokines TGF-beta and IL-10 rather than switch from Th2 to Th1
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28
Q

Outline treatments for FAD and AD

A
  • Anti-inflammatories
  • Glucocorticoids often with antibiotics
  • Removal of fleas in FAD
  • Avoidance of possible allergens
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29
Q

Describe the structure of Gram +ve

A
  • One cell membrane
  • Thick cell wall
  • Stain able to get stuck
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30
Q

Describe the structure of Gram -ve

A
  • 2 cell membranes
  • Thin cell wall
  • Stain cannot get in
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31
Q

Describe the structure of acid fast bacteria and explain their stainign properties

A
  • Mycolic acids in cell walls
  • Peptidoglycan layer linked to arabinogalactan, furhter linked to high molecular weight mycolic acids
  • Resist decolourisation by acid-alcohol, remain stained red colour of first stain in acid fast staining
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32
Q

Describe the structure of mycoplasma and explain their staining properties

A
  • Do have cell membrane but no cell wall
  • Hence do not stain Gram +ve
  • No distinct structural morphology
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33
Q

Describe the microscopic appearance of Streptococci

A
  • Long chains of cocci
  • Gram +ve
  • Acid fast
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34
Q

Describe the microscopic appearance of Staphylococci

A
  • Bunches of cocci

- Gram +ve

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35
Q

Describe the microscopic appearance of Diplococci

A
  • Join up as pairs
  • Cocci
  • Gram -ve
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36
Q

Describe the microscopic appearance of E. coli

A
  • Rod shaped

- Can be motile with flagella

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37
Q

Describe the microscopic appearance of Malassezia

A
  • Yeast appearance

- Snowmen

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38
Q

Describe the microscopic appearance of Actinomyces

A
  • Rod shaped, but clump to appear hyphal
  • Gram +ve
  • Non-acid fast genera of Actinomycetes
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39
Q

Describe the microscopic appearance of filamentous fungi

A

Hyphae containing multiple nuclei

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40
Q

Describe the microscopic appearance of Clostridium

A
  • Rod shaped
  • Endospores bottle shaped
  • Gram +ve
  • Endospores stained by malachite green
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41
Q

List some causes of skin disease

A
  • Parasitic
  • Bacterial
  • Viral
  • Fungal
  • Neoplastic
  • Nutritional
  • toxic
  • Physical
  • Congenital
  • Combination of above
42
Q

How does the keratin layer of skin protect against colonisation?

A
  • Not live cells
  • Dry, inhospitable
  • pH poor for bacteria
  • Shedding also sheds bacteria
43
Q

What feature of hair follicles allows them to be more easily colonised?

A
  • Secretions from glands

- Bacteria prefer to be bathed in serous fluid as contains nutrients beneficial to them

44
Q

Describe the normal skin flora

A
  • Sin and hair not sterile
  • Have normal resident flora incl bacteria and yeasts
  • Aid exlusion of pathogens but may also contribute to disease
45
Q

Give some examples of normal skin microflora

A
  • Bacteria: Micrococcus spp, Staphylococcus, Propionobacterium acnes, Bacilus, Clostridium (Gram +ve all)
  • Yeasts: Malassezia
46
Q

Outline how disease may occur in the skin

A
  • When virulent pathogens overwhelm defences
  • When resident flora are disadvantaged by local conditions
  • Opportunistic infection by commensals e.g. through trauma
47
Q

What is the effect of elevated temperature with humidity on bacterial population?

A

Substantial increases in aerobic and anaerobic bacterial populations

48
Q

What factors influence the colonising ability of microorganisms?

A
  • Temperature and humidity of skin
  • Occluded areas
  • Exposure to UV light
  • Diet impacting skin turnover
  • Hormonal changes altering gland activity and keratinisation
  • pH, salinity, nature of lipids
  • Defences present e.g. antimicrobial peptides (defensins) in sweat
49
Q

What are the colonisation niches based on?

A
  • Local secretions
  • Local pH
  • Contamination from local structure, mouth, prepuce and anus
  • Moisture etc
50
Q

List normal skin bacteria of the dog

A
  • Micrococcus spp.
  • Coagulase -ve Staphylococci
  • S. epidermidis, S. xylosus
  • beta-haemolytic Streptococci
  • Clostridium spp
  • Propionobacterium acnes
  • Acinetobacter spp.
51
Q

List normal hair bacteria of the dog

A
  • Bacillus spp
  • Micrococcus spp
  • Gram -ve aerobes
  • Staphylococcus pseudintermedius
52
Q

List normal hair follicle bacteria of the dog

A
  • Micrococcus spp
  • Propionbacterium acnes
  • Staphylococcus pseudintermedius
  • Bacillus spp
53
Q

List transient skin bacteria of the dog

A
  • Staphylococcus pseudintermedius, S. aureus
  • E. coli
  • Proteus mirabilis
  • Cornyebacterium spp.
  • Bacillus
  • Pseudomonas
54
Q

List normal skin bacteria of cats

A
  • Micrococcus spp.
  • Staphylococcus siimulans
  • beta-haemolytic streptococci
  • S. aureus
  • S. pseudintermedius
  • Acinetobacter spp
55
Q

List transient skin bacteria of cats

A
  • beta-haemolytic streptococi
  • E. coli
  • Proteus mirabilis
  • Pseudomonas spp
  • Alcaligenes spp,
  • Bacillus spp.
  • Staphylococcus spp.
56
Q

Describe Staphylococcus species as skin commensals

A
  • Gram +ve, pairs, tetrads or clusters, catalase positive
  • At least 30 species
  • Opportunistic pathogens
  • Colonies white, opaque
  • Some coagulase -ve are pigmented
  • Facultatitve anaerobes
57
Q

Describe Staphylococcus pathogenicity

A
  • Pyogenic
  • Minor trauma can predispose to disease
  • Number of virulence factors
  • Include: coagulase, lipases, elastase, proteinA inhibiting opsonisation, range of toxins
58
Q

Describe Malassezia

A
  • Commensal and opportunistic pathogen of cats and dogs
  • M. pachydermatitis
  • Breed dispositions
  • Common concurrent infection with Staph pseudintermedius
59
Q

What dog breeds are pre-disposed to higher levels of Malassezia?

A
  • Basset
  • Dachshunds
  • Cocker spaniels
  • West highland white terriers
  • genetic predispostion not sex linked
60
Q

What factors contribute to infection with Malassezia?

A
  • Hypersensitivity disorders
  • Keratinisation defects
    Hot, humid weather
61
Q

Describe Pseudomonas

A
  • Rod, Gram -ve, one or more polar flagella, aerobic, non-spore forming
  • Catalase and oxidase +ve
  • Readily found in environment
  • Wide range of opportunistic infections
  • Capsules of slime, sticky biofilms
62
Q

What species of Pseudomonas is most associated with opportunistic infections?

A

Pseudomonas aeruginosa

63
Q

Define resident microorganism

A

Can replicate on skin and can persist

64
Q

Define nomad microorganism

A

Organisms that colonise and reproduce on skin for short periods of time, do not stay long as are poorly adapted

65
Q

Define transient microorganism

A

Cannot replicate so only stay for shor periods

66
Q

List some non-immune defence mechanisms of the skin

A
  • Physical barrier
  • Desquamation
  • Poor conditions (dry, low pH)
  • Competition by normal flora
67
Q

List some innate immune factors of the skin

A
  • Keratin layer
  • Antimicrobial peptides
  • Protective substances such as mucus
  • Soluble complement proteins
  • Phagocytic cells
  • Intraepithelial lymphocytes and NK cells
  • Mast cells
  • Cytokines and chemokines
  • Inflammation
68
Q

List mechanisms by which microbes can avoid host defences

A
  • Antigenic variation
  • Inhibition of antigen processing
  • Inhibiting of complement activation
  • Resistance to phagocytosis
  • Inactivation of reactive oxygen species
  • Escape from phagolysosome following being engulfed
  • Production of cytokine receptor homologues
69
Q

Describe the overactivation by some Staphylococci and superantigens

A
  • Stimulation by superantigens e.g. Staphylococci spp
  • Superantigens over activate T-lymphocyte, bypassing normal process
  • Activation by binding MHC and lymphocytes, not through protein binding cleft
  • Can lead to cytokine production and inflammatory response
  • Uncontrolled immune response contibuting to pathology
  • Single protein by bacteria stimulating hypersensitivity reaction leading to responses in skin allowing further colonisation
70
Q

List factors impacting on cutaneous environment

A
  • Moisture/humidity
  • Damage
  • Normal tissue maintenance
  • Washing
  • Behaviour
  • Health
  • Physical breaches of barrier
71
Q

List the factors predisposing to proliferation of commensals

A
  • Hypersensitivity
  • Systemic disease
  • Damage/compromise of defence
72
Q

Compare colonisation and infection

A
  • Colonisation amy occur without infection e.g. commensals

- Infection will always require colonisation

73
Q

Give the most common skin infections for dogs, cats, cattle, pigs, sheep, horse

A
  • Dog: Staphyloccus pseudintermedius
  • Cat: subcutaneous abscesses (bites)
  • Cattle: dermatophytosis (ringworm)
  • Pig: greasy pig disease (Staphylococcus hyicus)
  • Sheep: sheep scab (parasite)
  • Horse: mud fever (Dermatophilus)
74
Q

Give examples of viral skin infections

A
  • Distemper

- Papilloma virus

75
Q

How can mastitis be described as a skin disease?

A
  • Surface colonisation of teats

- But also internal udder infection

76
Q

name the causative agent of Dermatophilosis

A

Dermatophilus congolensis

- Actinomycete

77
Q

Describe the structure of Dermatophilus congolensis

A
  • Gram +ve filamentous bacterium
  • Non-acid fast
  • Facultative anaerobe
  • Motile zoospore activated to form mycelium
  • 2 forms: filamentous hyphae and motile zoospores
78
Q

Describe infection with Dermatophilus congolensis

A
  • Wide host range
  • Causes exudative dermatitis with scab formation
  • Cattle goats and horses: cutaneous streptothrichosis
  • Horses: mud fever
  • Sheep: lumpy wool
79
Q

Describe the pathogenesis of Dermatophilus congolensis

A
  • Zoospore attracted to sites on skin
  • Germinate
  • Produce hyphae that penetrate into living epidermis
  • Spread from focal point in all directions
  • Penetration causes acute inflammatory reaction
  • Acute or chronic infections
  • Acute: filamentous invasionceases 2-3 weeks, lesions heal spontaneously
  • Chronic: affected follicles and scabs are sites from which intermittent invasions of non-infected hair follicles and epidermis occur
80
Q

Compare superficial, intermediate and deep mycological infection

A
  • Superficial: hair, skin, calws, limited to surface epidermis and outer layers of hair and claws
  • Intermediate: infections of dermis and subcutaneous tissues
  • Deep: subcutaneous and systemic infections
81
Q

List factors critical to establishment of mycological infection

A
  • Exposure to organisms
  • Critical mass/time of infective material
  • Ineffective grooming
  • Warm, humid environment
  • Pre-existing skin conditions
  • Poor immune status
82
Q

Give the anamorphic genera of Dermatophytes

A
  • Microsporum
  • Trichopyton
  • Epidermophyton
83
Q

Gives esxamples of yeasts and yeast-like organisms that can infect skin

A
  • Candida
  • Malassezia
  • Trichosporon
84
Q

Outline the pathogenicity of mycologicl infection

A
  • Grow on skin
  • Secrete enzymes
  • Break down cells
  • Use products of breakdown for own growth
85
Q

Describe dermatophytes

A
  • ~40 species
  • Septate, filamentous fungi
  • Initial infection, slow growing, radial, penetrate skin then grow out
  • 3 anamorphic genera
  • Grow exclusively in non-living tissue of skin, nails and hair (keratinised areas only)
86
Q

How are dermatophytes differentiated?

A

Features of their conidia

87
Q

Describe the appearance of Trichophyton dermatophytes

A
  • Macroconidia up to 50um long
  • Thin smooth walls
  • Microconidia ~4um
88
Q

Describe the appearance of Epidermophyton dermatophytes

A
  • Macroconidia up to 15um
  • Thin smooth walls
  • Microconidia absent
89
Q

Describe the appearance of Microsporum dermatophytes

A
  • Macroconidia up to 125um long
  • Thick rough walls
  • Microconidia ~4-7um
90
Q

Describe cattle ringworm

A
  • Mostly Trichopyton verrucosum
  • Less common T. mentagrophytes
  • Common in young stock, adults also affected
  • Close animal contact is risk factor
  • Affects animal and hide value
91
Q

Describe reservoirs for cattle ringworm

A
  • Spores can survive many months
  • Contaminated environment
  • Soil
  • Infected animals
  • Fomites
  • Asymptomatic canine adn feline carriers
92
Q

Describe the pathology of cattle ringworm

A
  • Incubation period 1 week
  • Fungus invades anagen hairs
  • By digestion of keratin
  • Hyphal growth only as far as keratinisation of hair takes place
  • Hair breaks = alopeca
  • Inflammatory response
93
Q

Describe deep mycoses

A
  • Infections invading deep into skin, many produce skin lesions secondary to systemic infections
  • Direct inoculations, ingestion or inhalation of spores
  • Can be divided into subcutaneous and systemic infections
94
Q

Give an example of a deep mycosis

A
  • Cryptococcus neoformans in cats
  • Cats with FIV increased risk
  • Anamorphic yeast producing capsules
95
Q

Describe bovine papilloma virus

A
  • Warts
  • Infectious disease of young cattle
  • Contact and minor abrasions
  • Usually self limiting
  • 5 strains, each different preferred infection site
96
Q

List key diagnostic techniques in dermatology

A
  • Examination of coat with lens
  • Flea combing
  • acetate tape prep
  • Cytology
  • richogram
  • Skin scrapings
  • Wood lamp examination
  • Fungal culture dermatophytes
  • Mckenzie toothbrush culture
  • bacterial culture and susceptibility testing
  • Skin biopsies
97
Q

Describe fungal culture for dermatophytes

A
  • Select broken hairs or those along edge of alopecic lesions
  • Toothbrush collection where pooly defined lesion
  • Common medium: dermatophyte test medium (DTM)
98
Q

Describe Wood’s lamp examination

A
  • For Dermatophytes
  • 50% of strains produce metabolites following hair invasion that fluoresce an apple-green colour when illuminated by lamp
  • Inexpensive
  • But poor sensitivity
99
Q

Describe trichograms for examination of Dermatophytes

A
  • Microscopic examination of plucked hair
  • Aim to get bulb and not fracture shaft
  • Immersed in mineral oil, coverslip, examine at X40
100
Q

Describe skin scrapes for examination of Dermatophytes

A
  • Scalpel blade coated with mineral oil scraped along skin

- Materal then placed on slide, coverslip, examine at X40 or X100

101
Q

What stain is commonly used for fungal examination?

A

Lactophenol cotton blue

Endo (30 decks)

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