SCYM Flow Cytometry Principles 4 — Questions and Answers
Question 1: What does the acronym 'MESF' stand for in flow cytometry standardization?
- Mean Emission Spectrum Frequency
- Molecules of Equivalent Soluble Fluorochrome (Correct answer)
- Maximum Excitation Signal Factor
- Median Expression Signal Function
Correct answer: Molecules of Equivalent Soluble Fluorochrome
MESF (Molecules of Equivalent Soluble Fluorochrome) is a quantitative unit used to standardize fluorescence intensity measurements across instruments.
Question 2: Which of the following is a consequence of under-compensation in multicolor flow cytometry?
- Populations appear falsely negative in the compensated channel
- Populations appear falsely positive in the channel receiving spillover (Correct answer)
- Scatter plots show increased cell debris
- The instrument acquires cells at a slower rate
Correct answer: Populations appear falsely positive in the channel receiving spillover
Under-compensation leaves residual spillover signal in adjacent channels, making cells appear falsely positive for markers they do not express.
Question 3: Which sample preparation step is critical for accurate immunophenotyping of whole blood?
- Fixing all cells with paraformaldehyde before staining
- Lysing red blood cells to reduce background interference (Correct answer)
- Heating the sample to 56°C to remove complement proteins
- Adding DNase to prevent cell clumping
Correct answer: Lysing red blood cells to reduce background interference
Red blood cell lysis is essential for whole blood immunophenotyping to remove erythrocytes that obscure leukocyte populations.
Question 4: In spectral flow cytometry, how is unmixing different from traditional compensation?
- Unmixing uses a single reference spectrum per fluorochrome across all detectors, while compensation corrects pairwise spillover (Correct answer)
- Unmixing requires more single-stained controls than compensation
- Unmixing is only applicable to viability dyes
- Unmixing replaces scatter parameters with fluorescence data
Correct answer: Unmixing uses a single reference spectrum per fluorochrome across all detectors, while compensation corrects pairwise spillover
Spectral unmixing uses the full emission spectrum of each fluorochrome across all detectors simultaneously, providing more accurate signal separation than pairwise compensation.
Question 5: Why is it important to use the same lot of antibody conjugate for compensation controls as for the experimental sample?
- Different lots may have different fluorochrome-to-protein ratios affecting spillover values (Correct answer)
- Different lots are always from different fluorochrome manufacturers
- Lot variation affects cell viability after staining
- Compensation controls must match the sample's isotype controls
Correct answer: Different lots may have different fluorochrome-to-protein ratios affecting spillover values
Fluorochrome-to-protein (F/P) ratios can vary between lots, altering spectral properties and spillover values, so the same lot ensures accurate compensation.
Question 6: What is the primary use of a viability dye in flow cytometry panels?
- To enhance fluorescence intensity of surface markers
- To identify and exclude dead cells from analysis (Correct answer)
- To permeabilize cells for intracellular staining
- To fix cells for prolonged storage before acquisition
Correct answer: To identify and exclude dead cells from analysis
Viability dyes mark dead cells (which non-specifically bind antibodies) so they can be excluded, ensuring immunophenotyping data reflects only live cells.
Question 7: What does a high event acquisition rate (events per second) risk in flow cytometry?
- Increased laser damage to the PMTs
- Coincident events where two cells pass through the laser simultaneously (Correct answer)
- Reduced fluorescence intensity from individual cells
- Loss of sheath fluid pressure causing cell damage
Correct answer: Coincident events where two cells pass through the laser simultaneously
High event rates increase the probability of two cells occupying the interrogation point simultaneously (coincidence), producing artifactual events.
SCYM Flow Cytometry Principles 4
What does the acronym 'MESF' stand for in flow cytometry standardization?