The Nude Mouse

The nude mouse gets its name because it has no hair. But far more interesting, it is also born without a thymus. These traits result when the mouse is homozygous for a recessive mutant gene designated Foxn1.

The photo (courtesy of Jackson Laboratory) shows a nude mouse (Foxn1^−/−) and its phenotypically normal heterozygous (Foxn1^+/−) littermate.

Because it lacks a thymus, nude mice cannot generate mature T lymphocytes. Therefore they are unable to mount most types of immune responses, including:

antibody formation that requires CD4⁺ helper T cells
cell-mediated immune responses, which require CD4⁺ and/or CD8⁺ T cells:
- delayed-type hypersensitivity responses (require CD4⁺ T cells);
- killing of virus-infected or malignant cells (requires CD8⁺ cytotoxic T cells);
- graft rejection (requires both CD4⁺ and CD8⁺ T cells)

The absence of functioning T cells prevents nude mice from rejecting not only allografts, but they cannot even reject xenografts; that is, grafts of tissue from another species.

These six photographs (courtesy of Dean D. Manning) show 6 different skin xenografts surviving on nude mice.

A. Human (mammal) skin after 60 days.
B. Cat (mammal) skin at 51 days.
C. Chicken (bird) at 32 days; the feathers were already present when the graft was made.
D. Chameleon (reptile) at 41 days.
E. Fence lizard (reptile)at 28 days.
F. Tree frog (amphibian) at 40 days.

Not only have nude mice answered many questions in immunology, but their ability to maintain human tissue have made them useful tools for investigating, for example, the properties of human cancers [Link].

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14 June 2011