T lymphopenia in genetically obese rats

Although obese animals are more susceptible to infection, the underlying causes are not fully known. In this study, long-term measurements were made of lymphocyte subsets in peripheral blood, spleen, and thymus in genetically obese Zucker (fa/fa) rats. Blastogenic response of splenocytes to mitogens was also examined. fa/fa rats developed obesity, hyperlipidemia, and hyperinsulinemia after 5 weeks of age. Flow cytometric analysis revealed that T cells in peripheral blood, spleen, and thymus were all reduced significantly in obese rats after 8 weeks of age compared to nonobese (Fa/-) littermates. All T-cell subsets examined, including CD4+ and CD8+ T cells, were similarly reduced in spleen and thymus as well as in peripheral blood with advance in age. In addition, proliferative responses of splenocytes to mitogens were significantly low in obese rats. These results indicate that long-term obesity may reduce the size of the T-cell pool and impair the responsiveness of splenocytes in rats.