Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN

Mice and rats account for over 90% of the animals used for biomedical research. The proper care of these research animals is critical to the outcome of experiments. There are general procedures that apply to the majority of these mice and rats, but some of the animals, such as the immunocompromised ones, require additional steps to be taken to sustain them for experimentation.

Commonly used immunocompromised mice include those that have naturally occurred in inbred mice and those that have been created through genetic engineering. The first immunocompromised mice used in research were "nude" mice. The BALB/c Nude (nu) mouse was discovered in 1966, within a BALB/c colony that was producing mice lacking both hair and a thymus. These athymic mice have an inhibited immune system that is devoid of T cells. The value of this animal was soon discovered for the use in studies of microbial infections, immune deficiencies, and autoimmunity. Although not as commonly used as the nude mouse, there is also a nude rat. The nude rat is T cell deficient and shows depleted cell populations in thymus-dependent areas of peripheral lymphoid organs. Another naturally occurring immune deficient mouse is the severe combined immunodeficiency mouse (SCID). These mice have a defect that impairs the production of functional B and T cells. With the inability to mount an adequate immune response, these mice can serve as host recipients for transplants of human cells. Several genetically-modified mouse strains with immune deficiencies are commercially available.¹ The severity of the deficiency varies with the genetic modification; however, all of the immunocompromised mice and rats are handled similarly.

This manuscript will describe the care of both immunocompetent and immunocompromised animals. The housing, diet, environmental requirements, and handling will be discussed for both groups of animals.

1. Handling immunocompetent (conventional) mice

It has been demonstrated that immune disorders of mice are very similar to those in humans.² As these animals have limited immunological capabilities, procedures in the handling and care of these animals have been designed to minimize the risk of infectious disease through the use of engineering controls, personal protective equipment for the animal care staff, and standard operating procedures; these mitigate contamination of caging and

The proper care and handling of animals used in biomedical research is crucial to the outcome of the experiments. Regulations and established guidelines dictate many of the practices used. However, additional measures are required for mice and rats that have immune deficiencies to mitigate accidental exposure to opportunistic pathogens. When practices adhere to established procedures, the health and wellbeing of the experimental animals is enhanced, and better experimental resulted are attained.