Production of murine leukemia virus in the immunodeficient wasted mutant mouse is associated with the wst allele

Expression of enhanced spontaneous and gamma-ray-induced apoptosis by lymphocytes of the wasted mouse

Mice bearing the autosomal recessive mutation wasted (wst/wst) display a disease pattern including increased sensitivity of lymphocytes to ionizing radiation, neurologic dysfunction, and immunodeficiency. Many of the features of this mouse model have suggested a premature or increased spontaneous frequency of apoptosis in thymocytes. Past work has documented an inability to establish cultured T cell lines, and abnormally high death rate of stimulated T cells in culture, and an increased sensitivity of T cells to the killing effects of ionizing radiations in the wst/wst mouse relative to controls. The experiments reported here were designed to examine splenic and thymic lymphocytes from the wasted and control mouse for signs of early apoptosis. Our results revealed enhanced expression of Rp-8 mRNA (which has been associated with apoptosis) in thymic lymphocytes and to a lesser extent in spinal cord in the wst/wst mouse relative to controls; expression of Rp-2 and Tcl-30 mRNA (also reported to be induced during apoptosis) were not detectable in spleen or thymus. Expression of Rp-2, Rp-8, and Tcl-30 mRNA in other affected tissues of the wasted mouse (brain and liver) were similar in the wasted mouse and controls. Thymus and spleen from the wasted mouse have reduced numbers of viable cells relative to controls. Higher spontaneous DNA fragmentation was observed in lymphocytes from the wasted mouse than in controls; however, gamma-ray-induced DNA fragmentation peaked at a lower dose and occurred to a greater extent in lymphocytes derived from the wasted mouse relative to controls. These results suggest that high spontaneous and gamma-ray-induced apoptosis in T cells of the wasted mouse may contribute to the mechanism underlying the observed lymphocyte and DNA repair abnormalities.

Cytokine and T-cell subset abnormalities in immunodeficient wasted mice

Wasted mice bear an autosomal recessive mutation (wst/wst) that manifests itself in neurologic abnormalities, immunologic deficiency, and faulty DNA repair evident by 21 days of age. The immunodeficiency is characterized by a reduction in the thymus-to-body weight ratio, low levels of IgA plasma cells at secretory sites, and increased sensitivity of T-cells to the killing effects of ionizing radiation. Experiments were designed to examine measures of T-cell activity in wasted mice. The initial experiments established that wst/wst mice have percentages of thymic and splenic Thy1+ cells equivalent to those of control littermates. Further studies of T-cell subpopulations with thymocytes revealed normal percentages of CD4+ and CD8+ cells in wst/wst mice; however, double-labeling experiments showed that CD8+ cells were predominantly CD4- in wst/wst mice, whereas in controls most CD8+ cells also expressed CD4+. Mesenteric lymph node T-cell subpopulations were similar in wasted and control mice. Because cytokines play a significant role in the regulation of the immune response and also interact with a variety of cellular systems, we examined the expression of different cytokine and related genes (IL1, IL2, IL2R, TNF, IL5, gamma-interferon, beta-TGF) in lymphoid tissues from wasted mice as well as from littermate and parental controls. Studies of RNA from lymphoid tissues of wasted mice using dot blot and Northern blot hybridizations revealed a deficiency of IL5 mRNA in thymus and spleen, decreased expression of IL2R in thymus (but not spleen), increased expression of IL1 in spleen (but not thymus), and increased expression of IL2, gamma-interferon, and beta-TGF in both spleen and thymus, relative to controls. Expression of TNF mRNA in lymphoid tissues was unaffected by the wasted mutation. These results suggest a role for cytokine imbalance in the pathogenesis of the immunodeficiency and other abnormalities of wasted mice.