22. Immunity and Immunodiagnosis of Bacterial Infections

Question 1

What type of immune response predominates with extracellular antigens?

Answer 1

Humoral response via T helper 2

Question 2

What are the potential consequences of exposure to a pathogen?

Answer 2

1. No infection
2. Infection and recovery
3. Overwhelming infection/death
4. Carrier state
5. Host pathology

Question 3

List some examples of nonspecific defenses against bacterial infections.

Answer 3

1. Physical barriers - skin and mucous membranes
2. Chemical barriers - lysozyme (in tears, saliva)
3. Mechanical barriers - coughing, sneezing
4. Inflammation

Question 4

What types of antigens are recognized by toll-like receptors (TLRs)?

Answer 4

• antigens commonly found on many different pathogens

- ex: Lipopolysaccharide (LPS), Flagellin, Peptidoglycan

Question 5

What type of hypersensitivity is involved in the cell-mediated defense against bacterial infections?

Answer 5

Intracellular by Delayed-type hypersensitivity. TH1 secretes INF-gamma which activates macrophages

Question 6

How are antibodies produced in a humoral response protective against bacterial infection?

Answer 6

• opsonization
• direct complement activation
• agglutination
• ADCC
• Toxin neutralization

Question 7

What role do antibodies play in post-streptococcal sequelae?

Answer 7

Acute rheumatic fever = Abs or cell-mediated response cross-reacts with cardiac tissue

Glomerulonephritis = Ab-strep Ag complexes deposited in glomeruli of kidney

Question 8

How was anti-streptolysin O (ASO) traditionally detected in serum?

Answer 8

Traditional test based on the ability of the Abs to neutralize streptolysin, keeping it from lysing RBCs

Question 9

Antigens from what bacterial species are used in the Weil-Felix test for the diagnosis of Rickettsia infection?

Answer 9

Ag from Proteus species

Question 10

What antibodies are measured in nontreponemal tests for T. pallidum infection (syphilis)?

Answer 10

Abs against cardiolipin - not specific for syphilis

Question 11

What does a positive nontreponemal test result signify in conjunction with a negative treponemal test?

Answer 11

False positive - other condition such as hepatitis, SLE, infectious mononucleosis

Question 12

How do the titers of treponemal and nontreponemal antibodies compare over the course of syphilis disease?

Answer 12

Nontreponemal - becomes positive in 1-4 weeks after primary stage

Treponemal - peaks early, about primary stage. Stays reactive for life

Question 13

Explain the confirmatory test used to detect anti-B. burgdorferi antibodies in serum.

Answer 13

Western blot
- B.burgdorferi antigens electrophoresed on a gel and then blotted onto nitrocellulose paper
- Pt serum incubated of paper (primary Ab)
- After washing, enzyme-labeled anti-human Ig incubated on paper (secondary Ab)
- After washing, enzyme’s substrate added to allow for visualization
Postive Ab = visible band
IgM = 2/3
IgG = 5/10