Immunocompromised mice are mice with weakened or deficient immune systems. These mice are often used in biomedical research because their lack of immune response allows for the study of certain diseases, or the testing of potential treatments, in a way that wouldn’t be possible in an immune-competent organism.

There are various types of immunocompromised mice, which are deficient in different aspects of the immune system. For instance:

1. Nude Mice: These mice have a genetic mutation that prevents them from developing a thymus, a key organ for T cell development. As a result, they lack functional T cells and have impaired immune responses. Nude mice are often used in cancer research, including the creation of xenograft models.
2. SCID Mice: SCID stands for “severe combined immunodeficiency.” SCID mice have a genetic mutation that impairs the development of both T cells and B cells, the two main types of immune cells. This makes them even more immunodeficient than nude mice.
3. NSG Mice (NOD scid gamma mice): These are a specific strain of SCID mice that also lack functional NK cells due to a deficiency in the IL-2 receptor gamma chain. They are one of the most immunodeficient types of mice and are frequently used in xenograft models.

The use of immunocompromised mice allows researchers to study human diseases in a whole-organism context, but it also comes with challenges. For example, because these mice lack a fully functional immune system, they must be carefully protected from infections. In addition, while they allow for the study of human diseases, the lack of an immune response can also limit the types of questions that can be answered in these models.