In an experiment, FITC-CD4 and PE-CD8 were used to stain thymocytes. The cells were then run through a flow cytometer and the data were plotted as CD4 vs CD8. The results are shown in the figure below and the following statements are made:A. Rearrangement of TCR-β locus is initiated in cells included in the quadrant containing 3.58% of the population. B. TCR-α locus rearrangement occurs in cells included in the quadrant containing 87.5% population. C. FITC-CD4 and PE-CD8 cannot stain the same cells. D. Rearranged TCR-γδ receptor is expressed on 7.06% population of cells.Which one of the following options represents the combination of all correct statements?

Correct option is A

Explanation:

A is correct: The double negative (CD4⁻CD8⁻) thymocytes (~3.58%) are early progenitors where TCR-β gene rearrangement begins.
B is correct: The double positive (CD4⁺CD8⁺) thymocytes (~87.5%) undergo TCR-α locus rearrangement and express the mature TCR-αβ receptor.
C is incorrect: FITC-CD4 and PE-CD8 can stain the same cells (double positive cells).
D is incorrect: TCR-γδ expressing cells are typically within the double negative or single positive CD8 populations, not the CD4 single positive (7.06%) population.

T cell development progresses from double negative (DN) → double positive (DP) → single positive (SP) stages.
TCR-β rearrangement is an early event in DN cells; successful rearrangement leads to DP stage with TCR-α rearrangement.
Flow cytometry with dual staining identifies these developmental stages based on CD4/CD8 surface markers.
TCR-γδ cells develop separately and are minor populations within thymocytes.