Thymic vasopressin (AVP) transgene expression in rats: a model for the study of thymic AVP hyper-expression in T cell differentiation.

The peptide arginine vasopressin (AVP) is present within tissues of the immune system and has been implicated in T cell differentiation. We have investigated the expression and production of AVP in the thymus of rats which carry a rat AVP transgene. A 100% increase in thymic AVP immunoreactivity (ir) was detected in transgenic (TG) animals compared to age-matched wild-type (WT) controls. When tissues from TG and WT thymuses were subjected to reversed-phase high-performance liquid chromatography, ir-AVP eluted as a single peak which co-eluted with the standard. Immunocytochemical staining identified the presence of AVP in large epithelial cells within the thymic cortex in both WT and TG animals. The AVP precursor product neurophysin was also detected in epithelial cells in WT and TG thymuses. In situ hybridisation histochemistry using a probe specific for transgenic AVP mRNA revealed that the AVP transgene was expressed in TG thymic cells with a similar morphology and distribution to those which expressed endogenous AVP peptide in WT animals. These results demonstrate that the cellular location and immunoreactive form of AVP expressed in TG animals are similar to that found in WT controls. Thus the TG rat appears to be a model of true physiological, rather than ectopic, over-expression of AVP in the thymus. The hyper-expression of AVP in the thymic epithelial cells of TG animals provides a model in which can be studied the influence of AVP on T cell development and differentiation within the thymus.