Immunohistochemical study of tyrosine phosphorylation signaling in the involuted thymus

Thymic involution has been reported to be an important parameter of the deg ree and duration of child abuse. In the present study, we assessed the stat us of tyrosine phosphorylation signaling, which is known to play a key role in the physiological function of the thymus, in involuted thymuses of abus ed children through immunohistological studies performed with anti-phosphot yrosine antibodies. We found that tyrosine-phosphorylated proteins were pre sent in high amounts in Hassall's corpuscles (HC) in the medulla of control thymuses. In involuted thymuses of abused children, expression of tyrosine -phosphorylated proteins was reduced with accompanying morphological change s of HC, such as reduction in size or calcification. These findings lead us to the suggestion that tyrosine phosphorylation signaling is reduced in in voluted thymuses of abused children and that reduction of the signaling may be associated with morphological changes of HC as observed in involuted th ymuses of abused children. In order to certify the suggestion, we investiga ted expression of tyrosine-phosphorylated proteins in involuted thymuses of stressed rats as well as in control thymuses. Immunohistochemistry reveale d that tyrosine-phosphorylated proteins were expressed in control thymuses, more abundantly in the medulla, and reduced remarkably in involuted thymus es of stressed rats. Further, immunoblot analysis also showed that expressi on of phosphotyrosine-containing proteins was reduced in thymus extracts of involuted thymuses of stressed rats, thus supporting the suggestion. Our r esults also raise the possibility that components of tyrosine phosphorylati on signaling could be a molecular marker for thymic involution. (C) 2000 El sevier Science Ireland Ltd. All rights reserved.