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General Med 1 > Path - Immu and Diagnostics - Exam 3 > Flashcards

Path - Immu and Diagnostics - Exam 3 Flashcards

1
Q

What are the general immune defects seen in children? And the elderly?

A

Children: Immature immune systems:

  • suboptimal antibody responses to bacterial infections and polysaccharide vaccines
  • allergic disease

Elderly: Immunosenescence:

  • suboptimal antibody responses to infections and vaccines
  • low CD8 T cell responses
  • cancer
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2
Q

How does the mother pass on antibodies to the child?

A
  • baby exposed to IgG in the placenta

- baby exposed to dimeric IgA in breast milk

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3
Q

What are the key differences in immune cells and antibodies between infants compared to adults?

A

a) neutrophils – higher blood count, BUT they are less responsive to chemokines
b) dendritic cells – lower stimulation of T cells
c) CD4 T cell helper function – skewed towards Th2 until 12 months old
d) CD8 T cell response – lower until 9-12 months old
e) IgG and IgA antibodies – higher in IgG1 and IgG3, but lower in IgG2, IgG4 and IgA until 13 years old.

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4
Q

Why do children have transient low IgG levels around 6 months?

A

The passively transferred maternal IgG has been greatly reduced and the baby is not producing much of its own IgG antibodies yet.

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5
Q

Why are babies particularly susceptible to encapsulate bacteria?

A

They are low in IgG2, which is the dominant IgG antibody response against encapsulate bacteria (polysaccharides). IgG2 and IgG4 reach adult levels slower than IgG3 and igG1.

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6
Q

Why is B cell activation by polysaccharides less efficient in babies? How can we get around this?

A

B cell activation by polysaccharides is enhanced by T cell activation, however they don’t have many active helper t cells yet.

Antibody responses against bacterial polysaccharides can be enhanced via:

a) protein conjugation of the capsular antigens of bacteria
- pneumococci
- H. influenzae B (Hib)
- meningococci
b) multiple recombinant protein antigens
- meningococci

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7
Q

Why do the elderly also have increased susceptibility to pneumococcal disease?

A

Lower opsonophagocytic antibody responses to pneumococcal polysaccharide vaccines.

Low opsonophagocytic antibodies is strongly correlated with low IgG antibody avidity.

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8
Q

What causes defects in B cell responses at both extremes of age?

A
  1. Naïve B cells
    a) Babies:
    - decreased expression of cell-surface receptors. They have lots of naïve B cells but they don’t do much yet.

b) elderly:
- decreased production of naïve B cells

  1. Germinal centers and memory B cells
    a) babies:
    - impaired germinal center function
    - relatively lower numbers of memory B cells compared with naïve T cells

b) elderly:
- impaired germinal center function

  1. Bone marrow and plasma cells
    A) babies – N/A

b) elderly – decreased access to plasma cell niches in bone marrow. Lots of fat deposits. Therefore relatively low number of naïve cells, and accumulation of memory and plasma B cells (but they are not necessarily controlled well, i.e. they could be monoclonal)

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9
Q

What is the difference between the thymus gland in a baby vs an elderly person?

A
  • baby: very large as they are generating lots of naïve cells
  • elderly: thymus gland atrophies around the age of 30.
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10
Q

The proportion of circulation CD8 T cells is increased in the elderly. What are they doing?

A

Reacting to infections such as CMV that have remained in their bodies.

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11
Q

Why is the cellular immune response affected by immunosenescence in the elderly?

A
  • decreased number of naïve T cells and T cell receptor diversity
  • increased number of memory CD4+ and CD8+ T cells, BUT…
    - decreases T cell receptor diversity
    - impaired function
  • decreased number and function of NK and dendritic cells
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12
Q

What immunizations should be received after the age of 65?

A
  • pneumococcal polysaccharide (PcP) vaccines
  • seasonal flu vaccine
  • VZV vaccine
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13
Q

What is one immune factor that contributes to increased cancer in the elderly?

A

Mechanisms of tumour control. In younger people the immune system might recognize and kill tumors. CD4 and CD8 T cells are very important in this. Tumors land up escaping the immune system in the elderly.

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14
Q

What are examples of pre-analytical, analytical and post analytical errors?

A

a) Pre-analytical – 60%
- wrong test required
- blood sampled from IV line
- wrong tube, incorrectly filled out
- labeling errors, wrong patient
- potassium issues
- MINIMIZE by using a phlebotomist

b) Analytical – 15%
- lab equipment malfunction
- failure to detect shifts or drifts in quality control
- sample mix-up
- sample contamination

BUT low rates due to:

  • strict quality control
  • internal and external quality control
  • 2 level validation and authorization

c) Post analytical – 25%
- errors in validation
- transcription error
- failure in reporting/interpretation
- excessive turnaround time
- delay in acting on the results (phone calls)

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15
Q

/What could cause elevated potassium levels?

A

a) leakage of K from cells:
- haemolysis
- excessive tourniquet use
- excessive first clenching
- clotting
- increased WBCs
- increased platelets
b) delayed separation
c) Sampled from a line
- K infusion

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16
Q

*What is a reference limit and reference interval?

A

A value where it is expected that a stated proportion of patients will lie in.

Reference Interval is the space between two reference limits.

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17
Q

How can we determine if a result is normal?

A
  1. Cumulative view of the results:
    - have they changed?
    - is the change significant?
  2. Repeat the test – is it reproducible?
  3. Does the RI for this test give a good indication of a particular patient’s ‘normal’ range? (i.e. they might be an exception)
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18
Q

Why do analyte values change?

A
  1. Normal bio variation – CVi
  2. Analytical variation – CVa.
    - generally the goal of analysis is to ensure CVa
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19
Q

What is the reference change value used for?

A

RCV = the difference required to state two test results are different.
For 95% confidence, Z=1.96.
See flashcard

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20
Q

What is the 95% CI? What is CV?

A

+/-1.96 x SD

SD = CV (coefficient variation) x mean

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21
Q

How can you tell whether two sub-populations are different and require their own reference interval?

A

The difference between the means of the two sub-populations is greater than 25% of the RI.

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22
Q

Define sensitivity in the setting of diagnostic testing.

A

Sensitivity – probability of those with the disease correctly detected by the rest

  • the true positive ‘rate’
  • high sensitivity = few people are missed
  • ΣTP/Σcondition present = a/a+c
  • if high, negative result will ‘rule out’ disease
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23
Q

Define specificity in the setting of diagnostic testing

A

Specificity – probability of those without the disease correctly excluded by the test

  • the true negative ‘rate’
  • high specificity = rarely test positive when person doesn’t have disease
  • ΣTN/Σcondition absent = d/b+d
  • if high, positive will rule in disease
24
Q

Define PPV of a test.


A

Positive Predictive Value

  • given a positive test, probability that the patient ahs the disease
  • ΣTP/ΣAll Positives = a/a+b
25
Q

Define NPV of a test.

A

Negative Predictive Value

  • given a negative test, the probability that the patient doesn’t have the disease
  • ΣTN/ΣAll Negatives = d/c+d
26
Q

Demonstrate an understanding of the effect of disease prevalence on PPV and NPV of a test.

A

As the prevalence increases, the PPV increases and NPV decreases.

27
Q

How are likelihood ratios calculated and what do they mean?

A

LR positive test = sensitivity/1-specificity
- i.e. probability of +ve test in a person with D/prob +ve test in person without D

LR negative test = specificity/1-sensitivity
- i.e. probability of -ve test in a person without D/prob -ve test in person with D

The “positive likelihood ratio” (LR+) tells us how much to increase the probability of disease if the test is positive. On the other hand, the “negative likelihood ratio” (LR-) tells us how much to decrease it if the test is negative.

LR+ >10 or LR-

28
Q

*What tests are available for diagnosis of some common immune disorders?

A
  • SLE (lupus):
  • ANA Testing
  • confirm with positive ENA
  • low C3 and C4
  • Coeliac disease:
    HLA typing
  • Allergy:
    allergen-specific IgE levels
  • CVID (common variable immune deficiency) vs specific antibody deficiency:
    immunoglobulin measurement
  • HIV:
    western blot and blow cytometry
29
Q

How does an ANA test work?

A
  • hep-2000 cells
  • test reported by titre and pattern, not specific
  • need to confirm positive ANA results with second (specific) assay
  • sensitive but not specific

a) homogenous
- SLE
- drug induced lupus
- autoimmune hepatitis

b) speckled
- SLE
- sjorgens syndrome
- mixed CT disorder

c) membrane
- anti-phospholipid syndrome

d) nucleolar (homogenous nucleus)
- systemic sclerosis

e) cytoplasmic
- mytosis

f) centromere
- CREST syndrome

30
Q

What would you expect to see in histology for coeliac disease?

A

Hypersensitivity to cereal proteins results in abnormal mucosal lining of intestines – vili covered in immune cells. Snowed over.

31
Q

How is coeliac disease tested for?

A

HLA typing – Human leukocute antigen
Identified with EIA - enzyme immuno assay.

  • assay of auto-antibodies to tTg and/or anti-gliadin – high sensitivity and specificity
  • HLA DQ2 and DQ8 are useful to exclude CD if not there
  • Neg IgA anti-tTg and neg DQ2 and DQ8 make CD very unlikely
  • If DQ2 or DQ8 positive, CD not excluded
  • If IgA anti-tTg is high, CD very likely
  • Gold standard – biopsy
32
Q

What are the main symptoms of anaphylaxis and what mediates it?

A
  • bronchoconstriction
  • hypotension
  • rash

Mediated by allergen specific IgE antibodies.

33
Q

How are allergies diagnosed?

A
  1. Immunoassay (allergen specific IgE levels)
    - not influenced by medication
    - not influenced by skin disease
    - does not require expertise
    - quality control possible
    - expensive
  2. Skin Prick Test
    - higher sensitivity
    - immediate results
    - requires expertise
    - cheaper
34
Q

In what situations would you perform an allergen specific IgE levels in preference to a skin prick test and why?

A
  • recent antihistamine use and eczema
  • history of anaphylaxis – may have severe reaction
  • young children – distressing
  • persistent severe/unstable asthma
  • if they are on beta-blockers (just incase of anaphylaxis)
35
Q

/How would you interpret Ig results in terms of CVID and specific antibody deficiency?

A
  1. CVID probable:
    - >2 years
    - serum IgG and IgA low for age
    - poor response to vaccines
  2. CVID possible:
    - one Ig isotype is low
  3. Specific Antibody deficiency:
    - recurrent infections with low IgG subclass only AND impaired response to vaccination
  4. Excluded:
    - isolated IgAD or IgG subclass deficiency with normal vaccine response
36
Q

/How is flow cytometry performed for HIV?

A
  • method to measure size, granularity and phenotyping at individual cell level
  • cell markers (are antigens normally found on cell surface) used to differentiate
  • I.e. CD3, CD4, CD8 (very low if HIC), CD19 (B cells)
  • Fluorochrome conjugated to specific antibodies to stain specific cells
  • Flow through cytometer with light detectors
37
Q

*Outline the broad categories of tests used in the diagnostic microbiology laboratory

A
  1. microscopy
  2. culture
    - bacterial
    - viral
    - fungal
  3. detection of microbial components
    - antigen detection
    - detection of nucleic acid
  4. serology – detection of specific antibodies in serum
38
Q

*Describe the types of microscopy and their typical uses

A

a) bright field
- H&E
- gram stain
- wet prep of vaginal epithelial cells
b) dark field
- T. pallidum
c) phase contract
d) fluorescence
i. non-specific fluorophore
ii. Can be made specific with fluorophore labeled monoclonal antibodies
- legionella DFA
- Rickettsiae
e) electron
- HSV
- adenovirus
- influenza
- pox

39
Q

Explain the advantages and disadvantages of culturing microorganisms

A

Advantages:
- antibiotic susceptibility testing

Disadvantages:

  • need to know most likely pathogens as particular conditions will not suit all pathogens – nutrition, gaseous atmosphere, temperature, incubation time
  • fungus is very labor intensive:
  • dependent on morphological features
  • most grow slowly – sometimes weeks
  • doesn’t work with viruses
  • doesn’t work with everything – some can’t be visualized with routine stains, are too small, too slow, too difficult to grow or tests aren’t sensitive enough.
40
Q

Explain in broad terms the range of identification tests used in the diagnostic laboratory, from the simple to the high-tech.

A

Bacterial Identification:

  • catalase test
  • coagulase test
  • oxidase test
  • many more
  • Kit form of biochemical reactions, i.e.
  • i) API system. Pos or neg reactions given a numerical score, combined to give ID code, compared to database.
  • ii) Vitek Card
  • iii) MALDI-TOF – steel plate – laser – unique protein spectrum compared on extensive database
  • iv) 16s ribosomal RNA gene analysis – this gene has highly conserved regions (common among all bacter) and highly variable. Universal PCR primers can enable amplification of hyper variable regions, which are sequences and databased.

Fungal Identification:

  • yeasts - often identified using biochem reactions, i.e. API 20C
  • moulds – generally visual:
  • colony appearance
  • microscopy of mycelia and conidia
  • features can take weeks

Detection of microbial compontents:

  • Antigens:
  • IFA
  • EIA
  • Radioisotope
  • Particle agglutination
  • PCR test (nucleic acid amplification)

Serology:
- titre

41
Q

Describe antigen detection and how it provides rapid detection/identification

A
  • monoclonal antibodies against microbial agents produced in lab animals
  • antibodies can be labeled to enable detection:

a) IFA = immunofluorescent assays (IFA)
- fluorophore – shine UV to reflect visible fluorescence
- antibodies attach to infected cells so they fluoresce

b) EIA = enzyme immunoassay
- enzyme – colorless substrate converted to colored dye
- prepared in microtitre plates
- wells coated with antibody specific to pathogen being tested
- if antigen present, it is captured by antibodies.
- wells washed
- enzyme labeled antibody solution added, sticking to trapped antigens
- wells washed
- solution with enzyme’s colorless substrate added
- enzymes act on substrate and it develops color - +ve
- intensity read on spectrophotometer

c) radioisotope – detectable radioactivity
d) Particle agglutination

42
Q

Describe the principles of the PCR test and its advantages.

A

Nucleic acid amplification

Must know part of genetic sequence of pathogen being sought, and must choose target within that sequence that:

a) is not shared with other microorganisms
b) present in all strains of pathogens

PCR test:
Number of copies of the target = 2^n, where n = number of cycles.

a) Conventional gel-based PCR:
- Amplicons (piece of DNA or RNA that has been amplified) detected
b) Real time PCR
- each amplicon produced a light single. As amplicon number increases, intensity peak.

Advantages:

  • shorter window period – can detect during incubation period
  • detects low levels of viral RNA or DNA
  • can detect mutants
  • highly sensitive and specific
43
Q

Describe the antibody response to infection and how this is applied to diagnostic testing.

A

First exposure:
- IgM class antibody specific to the pathogen appears in several days to ~1 week
- persist for several months
- IgG class antibody appears in 1st or 2nd week
- persists for decades to life
Second exposure:
- IgM response absent or small
- Brisk IgG response, may be enough to prevent symptomatic infection

Therefore:

  • if IgM detected – must have been infected within last several months (prone to false positives and varies from pathogen to pathogen)
  • if IgG – has been infected some time in the past
  • Seroconversion – significant increase in IgG titre between acute and convalescent (recovering)
44
Q

Explain the meaning of an antibody titre.

A
  • 8 wells, each with 50uL of dilutent
  • add 50ul serum to first (pre diluted to 1:5) and mix
  • take 50ul from 1 and add to 1. Continue.
  • Result: ratio starts at 1:10, ends 1:1280, doubling each well
  • Therefore, if antibody present in serum, its concentration will diminish progressively
  • Test each well for antibody (many different tests) – each well either + or –
  • Some use RBCs as indicators, i.e. RBC pellet at bottom = +
  • 96 well microtitre plate can test 12 specimends
  • If same patient goes up 2 spots over a time period, there has been a 4x increase in titre, therefore recent infection.
  • Other tests give ‘detected’ or ‘not detected’ results, but this gives titre
45
Q

Explain the meaning and role of acute and convalescent antibody testing.

A

Acute – person has infection
Convalescent – person is recovering from infection

Seroconversion – significant increase in IgG titre between acute and convalescent (recovering)

46
Q

What is the difference between passive versus active immunity?

A

Active immunity:
Protection produced by person’s own immune system.
Usually lasts long.

Passive immunity:
Protection transferred from another person of animal as antibody.
Usually short lived.

47
Q

What are the sources of passive immunity?

A
  • heterologous hyperimmune serum
  • maternal antibodies (only IgG)
  • homologous pooled human antibody
    - IV Ig
  • homologous human hyperimmune globulin
    - VZV Ig
    - Hb Ig
48
Q

What is the general aim of vaccination?

A

Aim:
To provoke specific:
- humoral immunity (antibody)
- cell mediated immunity (T cells)
- immunological memory for LT protection (B and T cells)
That will provide protection against infectious disease.

The more similar a vaccine

49
Q

What is the mechanism of action for the ideal vaccine?

A
  1. Taken up by antigen-presenting cell
  2. Activates both T and B cells to give effector 
and memory cells
  3. generate Th and Tc cells to several epitopes
  4. persistence of antigen to continue to recruit B memory cells and produce antibody
  5. Results in sterilizing immunity
  6. Generates long-lived plasma cells that 
produce persistent antibody
  7. Does not result in excessive inflammation or affect response to other vaccines i.e. safe
50
Q

What are live vaccines?

A
  • attenuated (reduced in virulence) organism which replicates in the vaccine/host
  • act as natural infection
  • high levels of neutralizing antibody on re-exposure
51
Q

What are inactivated vaccines?

A

Killed microorganisms, their virulence determinants or their toxins

i) Whole cell:
- suspensions of killed organisms

ii) Fractional Vaccines:
- contain one or a few components of organism important in protection

  • Cannot replicate
  • Antibody responses related to quantity and potency of vaccine
  • Often needs adjuvant
  • Given in divided doses
  • Local reactions common
  • Duration of immunity variable
52
Q

What are the differences between live attenuated and inactivated vaccines (in terms of advantages and disadvantages)?

A
  1. LIVE:

Advantages:

  • good response to single dose
  • full range of B and T cell responses to many different epitopes
  • local and systemic immunity
  • long lasting immunity
  • better antibody persistence

Disadvantages:

  • reversion to virulence
  • may cause disease in immunosuppressed
  • interference by passive maternal antibody
  • more likely to cause disease like symptoms
  • stability – sensitive to heating
  1. INACTIVATED:

Advantages:

  • minimal interference from circulating antibody
  • wont revert to virulence
  • less likely to cause disease like symptoms

Disadvantages:

  • generally not as effective
  • generally require >1 dose
  • mostly humoral immune response
  • antibody titre falls over time
  • Given in divided doses
  • Local reaction common
  • Duration of immunity variable
53
Q

Discuss polysaccharide vaccines

A

a) pure polysaccharide
- most important virulence factor
- produce T-cell independent antibody response
- poor antibody responses in young children, immunocompromised and elderly
- antibodies low avidity and lack functional activity
- do not induce immunologic memory
- antibody persistence is poor
- may induce immunological hyporesponsiveness to subsequent dose

b) conjugate polysaccharide – i.e. bacterial meningitis
- polysaccharide attached to carrier protein
- presentation of protein peptides recruits T-cell help for polysaccharide specific B-cell
- T cell-dependent antibody response
- High avidity antibody with functional activity
- Induce immunologic memory

54
Q

What are the benefits of combined vaccines?

A
  • less visits to GP
  • less injections

Combining different antigens may affect immune responses:

  • epitope suppression
  • degradation of antigen
  • different time frame of immune responses
  • may enhance immune response
55
Q

What are adjuvants?

A

Adjuvants: substances used to improve the immune system’s response to antigens (amplification of immune response)

They result in:

  • earlier immune response
  • improve magnitude of response
  • induce appropriate immune response
  • increase length of response

Examples:

  • Iscomatrix (CSL)
  • MF59 (Novartis)
  • *ASO4 (GSK)
56
Q

Describe the difference between an adjuvant and a conjugate in vaccination

A

A conjugate vaccine is created by covalently attaching a poor (polysaccharide organism) antigen to a carrier protein (preferably from the same microorganism), thereby conferring the immunological attributes of the carrier on the attached antigen.

An adjuvant is a substance that is formulated as part of a vaccine to enhance its ability to induce protection against infection. Adjuvants help activate the immune system, allowing the antigens— pathogen components that elicit an immune response—in vaccines to stimulate a response that leads to long-term protection.

General Med 1 (24 decks)

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