Effects of castration on the lymphocytes of the thymus, spleen and lymph nodes.

It is well known that the thymus plays an important role in the development and maintenance of a competent immune system. The thymus atrophies with age, a process that is accelerated after puberty when there is elevation of serum sex steroid levels. We have used a panel of commercial monoclonal antibodies against various T and B cell surface markers to investigate the post-castration histological alterations in the thymus, spleen and lymph nodes of male Sprague-Dawley rats. Castration of 5-week-old male rats produced a significant increase in thymic weight (P < 0.05) compared to age-matched intact animals. The major observations from the immunohistochemical studies were post-castration elevations in staining for total T cells (MRC OX 19 and W 3/13), CD8 cells (MRC OX 8), B cells (MRC OX 12 and MARK-1) and cells bearing activation markers such as IL-2 receptor (MRC OX 39), transferrin receptor (MRC OX 26) and major histocompatibility class II antigen (MRC OX 6). These data suggest that following castration there is an increase in the ability of lymphocytes to respond to activation. As a result, there are elevated numbers of immature thymocytes within the thymus that undergo differentiation/maturation and consequently produce an increase in peripheral T and B cells.