A B6 mouse (H-2b haplotype) was crossed with a CBA mouse (H-2k haplotype) to generate F1 progeny. The following skin transplant experiments were then performed:
A. Graft from B6 mouse to CBA mouse
B. Graft from F1 mouse to B6 parent
C. Graft from F1 mouse to CBA parent
D. Graft from F1 mouse to F1 mouse
E. Graft from B6 mouse to F1 mouse
Which one of the following options represents all recipients in which the graft is tolerated?

Correct option is D

Correct Answer
(d) E
Explanation:
The F1 mouse expresses both H-2b and H-2k MHC haplotypes and is therefore immunologically tolerant to antigens from either parent. When a graft from a B6 mouse (H-2b) is transplanted into an F1 recipient, the graft is accepted because all donor MHC molecules are recognized as self by the F1 immune system. Other graft combinations involve MHC mismatch that leads to rejection.
Information Booster
· F1 hybrids express MHC molecules from both parental strains
· Parent → F1 grafts are tolerated due to shared MHC antigens
· F1 → parent grafts are rejected because the parent recognizes the non-shared haplotype as foreign
· Skin graft rejection is primarily mediated by T-cell recognition of MHC differences
· This principle is fundamental in transplantation immunology experiments
Additional Knowledge
A is incorrect because B6 (H-2b) grafts are rejected by CBA (H-2k) mice due to complete MHC mismatch.
B and C are incorrect because F1 grafts express an additional MHC haplotype not present in the parent, leading to rejection.
D represents a syngeneic (genetically identical) graft and is tolerated, but it is a trivial control and not the informative transplant outcome tested by the options.