Prac Quiz 1

Question 1

ELISA (Enzyme-Linked Immunosorbent Assay)

Answer 1

Detects specific antibodies (e.g., IgG, IgM, IgA) or antigens related to infections like HIV, hepatitis, or COVID-19.

Question 2

Flow Cytometry

Answer 2

Measures the presence and quantity of specific immune cells (e.g., CD4+ T cells in HIV infection).

Question 3

Western Blot:

Answer 3

Confirms the presence of specific proteins (e.g., HIV proteins) after ELISA screening.

Question 4

PCR (Polymerase Chain Reaction):

Answer 4

Detects viral or bacterial DNA/RNA, highly sensitive for diagnosing infections like TB or COVID-19.

Question 4

• Indirect ELISA:

Answer 4

• Process: Antigen is coated on the plate, followed by a primary antibody from the sample and a secondary enzyme-linked antibody.
  
  • Use: Commonly used to detect antibodies in serum, such as in HIV testing.

Question 5

Immunological Basis of the Mantoux Test

Answer 5

is used to diagnose tuberculosis (TB) infection. The test involves intradermal injection of purified protein derivative (PPD), which is derived from Mycobacterium tuberculosis.

Immune Response: If the person has been exposed to TB, their immune system will recognize the PPD and mount a delayed-type hypersensitivity (DTH) reaction. T cells release cytokines that recruit macrophages and other immune cells, leading to induration (a raised, hardened area) at the injection site.
* Interpretation: A positive test indicates past or current TB exposure, but does not differentiate between active TB and latent infection.

Question 6

• Direct ELISA:

Answer 6

Process: Antigen is directly coated onto the plate, and an enzyme-linked antibody is applied for detection.
* Use: Detects the presence of antigens like viral proteins

Question 7

Sandwich ELISA:

Answer 7

• Process: A “capture” antibody is first coated on the plate, followed by the antigen, then a second enzyme-linked detection antibody.
  
  • Use: Highly specific, used for detecting specific proteins or antigens like cytokines.

Question 8

Competitive ELISA:

Answer 8

• Process: Antigen in the sample competes with labeled antigen for binding to the antibody.
  
  • Use: Often used when the antigen is small or difficult to measure directly, like hormone levels.

Question 9

4. Steps of a Sandwich ELISA

Answer 9

1. Coat Plate: A capture antibody specific to the target antigen is coated onto the ELISA plate.
   
   2. Block Plate: Non-specific sites on the plate are blocked to prevent false positives.
   3. Add Sample: The sample containing the antigen is added; the antigen binds to the capture antibody.
   4. Add Detection Antibody: A second antibody, which is enzyme-linked and specific to a different epitope on the antigen, is added.
   5. Add Substrate: An enzyme substrate (like TMB) is added, leading to a color change.
   6. Stop Reaction and Measure: The reaction is stopped with acid, and absorbance is measured at 450 nm to quantify the antigen.

Question 10

Quantiferon-Gold test

Answer 10

an ELISA-based assay used to diagnose latent tuberculosis infection (LTBI).

*	Principle: Blood samples are incubated with TB-specific antigens (ESAT-6, CFP-10). If the patient has TB infection, their T cells will release interferon-gamma (IFN-γ).
*	Detection: IFN-γ is then measured using ELISA, where a higher level indicates TB infection.
*	Use: It’s preferred over the Mantoux test as it doesn’t require a follow-up visit and is not affected by prior BCG vaccination.

Question 11

Interpreting and Discussing ELISA Results

Answer 11

• Positive Result: A higher absorbance reading compared to the control indicates the presence of the target antigen or antibody in the sample.
  
  • Negative Result: A low or baseline absorbance similar to the negative control suggests the absence of the target antigen or antibody.
  • Control Importance: Positive and negative controls are crucial for validating the assay and ensuring the results are reliable.

Question 12

Comparison of Diagnostic Tests for Tuberculosis

Answer 12

• Mantoux Test (TST):
  
  • Advantages: Simple, low-cost, widely available.
  • Disadvantages: Requires two visits, false positives due to BCG vaccination, cross-reactivity with non-TB mycobacteria.
  • Quantiferon-Gold ELISA:
  • Advantages: Single visit, unaffected by BCG vaccination, more specific for TB.
  • Disadvantages: More expensive, requires laboratory facilities, and a blood draw.
  • PCR (e.g., GeneXpert):
  • Advantages: Rapid, specific for TB DNA, detects rifampicin resistance.
  • Disadvantages: Expensive, requires specialized equipment, cannot distinguish between live and dead bacteria.

Question 13

• Q: How does an ELISA detect the presence of an antigen or antibody?
  *

Answer 13

A: Through enzyme-linked antibodies that catalyze a color change when the substrate is added.