Homozygotes are deficient in both B and T cell function. Their spleen cells do not respond to either B or T cell mitogens and they are unable to reject skin grafts. They lack detectable B cells and pre-B cells. In spite of the small thymus and lack of functional T cells, the Thy1 marker is present on a majority of cells recovered from the thymus, and T cell lymphomas occur in 10 per cent or more of affected mice. Prkdc^scid specifically impairs differentiation of stem cells into mature lymphocytes. Myeloid cell differentiation is not affected. The basic defect in these mice appears to be in the lymphoid stem cells and not in the cellular environment, since functional T and B cells are found in mice reconstituted with normal bone marrow (J:30980, J:7343). However, full reconstitution of the immune deficiency occurs only after irradiation of the recipients, indicating that Prkdc^scid/Prkdc^scid mice may have normal numbers of a radiation-sensitive stem cell that has defective proliferative capacity (J:8299).

The rearrangements of immunoglobulin and T cell receptor genes that normally occur in B and T lymphocytes are not found in homozygous Prkdc^scid mice. However, in Abelson leukemia virus-transformed B cells of these mice and in their occasional T cell lymphomas, rearrangements, most of which are abnormal, are found. This suggests that scid may act through an effect on the recombinase system catalyzing the assembly of immunoglobulin and T cell receptor genes, and that lymphocytes with these defects are not able to develop further (J:8420).

Although most Prkdc^scid homozygotes fail to produce immunoglobulin and functional T-cell receptor, some produce these products at low levels, with an occasional mouse with nearly normal levels of serum immunoglobulin, the criterion usually used tomeasure the effects of Prkdc^scid. This phenomenon is referred to as "leakiness" of the VDJ recombination defect (J:4610).Homozygous Prkdc^scidmice are fertile and, under specific pathogen-free conditions, may survive a year or more(J:6958).

The Prkdc^scid mouse has been widely used in studies of the immune system, in particular of VDJ recombination in T and B lymphocytes. Its lack of immunocompetence has made it useful in transplantation studies, particularly transplantation and development of metastasis in human tumors. The interaction of infection, immunity, and disease processes have been studied with these mice. Poole (J:31292) offers a brief review of the nature and usefulness of the Prkdc^scid mouse, with key references to the very extensive literature.

Mutant mRNA does not appear to differ from wild type although protein expression is reduced more than 10-fold. Mutant protein is defective for nuclear association but exhibits normal DNA-binding ability.

NOD.Cg-Prkdc^scid B2m^tm1Unc mice lack mature lymphocytes and serum Ig, are MHC class I deficient, B and T cell deficient, C-5 deficient (Hc⁰), and have low NK cells. These mice display accumulation of iron in the liver and rapid clearance of human IgG1.

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