The immune system of thymectomized and lethally irradiated (A × B) F₁ mice (H-2ᵃ/ᵇ) were reconstituted by grafting thymus from Strain B mice (H-2ᵇ) and with (A × B) F₁ bone marrow cells. These mice were then infected with lymphocytic choriomeningitis virus (LCMV). The CD8⁺ cytotoxic T lymphocytes from the reconstituted mice were then co-cultured with the following target cells in vitro:

A. Uninfected fibroblast cells from (A × B) F₁ mouse
B. Uninfected fibroblast cells from strain-A mouse
C. Uninfected fibroblast cells from strain-B mouse
D. LCMV infected fibroblast cells from (A × B) F₁ mouse
E. LCMV infected fibroblast cells from strain-A mouse
F. LCMV infected fibroblast cells from strain-B mouse

Which of the options below indicate the cells that will be lysed by the CD8⁺ cytotoxic T lymphocytes from the reconstituted mice?

Correct option is C

Explanation-

A. Uninfected fibroblast cells from (A × B) F₁ mouse
Infection status:  Not infected (no viral peptide)
MHC type:  H-2ᵃ/ᵇ → includes H-2ᵇ
Interpretation: No viral antigen → CD8⁺ T cells have nothing to recognize.
Conclusion:  Not lysed

B. Uninfected fibroblast cells from strain-A mouse
Infection status:  Not infected
MHC type:  H-2ᵃ only
Interpretation: No infection AND lacks H-2ᵇ → not a match for CTLs.
Conclusion:  Not lysed

C. Uninfected fibroblast cells from strain-B mouse
Infection status:  Not infected
MHC type: H-2ᵇ
Interpretation: Although MHC matches (H-2ᵇ), there’s no viral peptide presented.
Conclusion:  Not lysed

D. LCMV-infected fibroblast cells from (A × B) F₁ mouse
Infection status:  Infected with LCMV
MHC type:  H-2ᵃ/ᵇ → includes H-2ᵇ
Interpretation: Viral peptides presented on H-2ᵇ → matches MHC restriction of CTLs
Conclusion: Lysed

E. LCMV-infected fibroblast cells from strain-A mouse
Infection status:  Infected
MHC type:  H-2ᵃ only (no H-2ᵇ)
Interpretation: Although infected, the MHC class I does not match T cell education (H-2ᵇ)
Conclusion:  Not lysed (CTLs can’t “see” the peptide)

F. LCMV-infected fibroblast cells from strain-B mouse
Infection status:  Infected
MHC type:  H-2ᵇ
Interpretation: Viral peptides presented on H-2ᵇ → matches CD8⁺ T cell’s restriction
Conclusion:  Lysed

Only D and F cell types meet both criteria:
               1.   Infected with LCMV (they present viral antigen).
               2.   Express H-2ᵇ MHC I (which the CD8⁺ T cells are restricted to).

So, the correct answer is option c - D and F only.