Thymic stromal alterations in mice undergoing a chronic graft-versus-host reaction.

Graft-versus-host induced immunosuppression has previously been shown to be accompanied by severe morphological changes in the thymus; furthermore chronic GvH could become acute by grafting a normal syngeneic thymus, suggesting a functional defect in the autologous thymus. In this work, we monitored the changes occuring in two biologically active thymic stromal fractions during a state of chronic GvH reaction. It was thus observed that a soluble thymic factor (STF), normally found in the reticuloepithelial cells, was lost, and that an insoluble thymic fraction (ITF) found in a double basement membrane surrounding medullary blood vessels, became markedly hypertrophied. These changes are interpreted as being possibly related to the state of immunosuppression by interfering with normal T cell differentiation and traffic through the thymus.