The Cytological Study Of Cervical Thymus In Mice

Thymus is the central lymphoid organs, which is the main organ of the occurrence, development and differentiation of T lymphocytes. It plays a central role in cellular immunity, and degenerates after sexual maturity. Terszowski and his colleagues found that there was a second thymus in the neck of BALB/c and C57BL /6 mice respectively. The neck thymus had typical medulla-cortical structure as the the thoracic thymus, and can support T cell development. In order to investigate the exist of the neck thymus in other strain mice and its relationship with the thoracic thymus and lymphoid nodes in neck, the structure of the cervical thymus, thoracic thymus and cervical lymph nodes in Kunming mice was studied by microscopic and EM methods in this paper, The major results were as follows:1. Cervical thymuses were also found in Kunming mice, and their location and number varied from specimen to specimen. It located superficially or concealed under the cervical muscle strings in the ventral necks of mice. Although the cervical thymuses could be found in both left and right side of the neck in mice, there were more in the left. Cervical thymus is oval in shape, ivory in color, and surrounded by connective tissue membrane. By dissection,93.33% Kunming mice were found to have cervical thymus, of them 33.93% mice had one cervical tymus,55.35% had two and 10.71% had three.2. Cervical thymus and thoracic thymus had the similarly basic structure and cell elements in Kunming mice and the structure of cervical thymus is much different from the lymphoid node. Cervial thymus can be divided into two regions as in thoracic thumus:cortex and medulla. On the other hand, Cervical thymus had no lobules as thoracic thymus. Cervial thymic microenvironment also contained the epithelial cells, thymic corpuscle, macrophages, myoid cells and others.3. Although Cervical thymus had the degeneration phenomenon with mice growth as thoracic thymus, the growth and degenerating pattern is different from the later. Cervical thymus increased gradually from 1 week after birth, and reached the largest at 7 weeks, then gradually became smaller and smaller. Its color became from ivory to yellowish. Cervical thymus index was greater in 1 week than 2-3 weeks, reached the maximum at 4 weeks, and then decreased with age. Thoracic thymus reached the largest at 4 weeks, then gradually became smaller and smaller. Thoracic thymus shows yellow in color and irregular in structure at 48 weeks especially. Thoracic thymus index reached the maximum at 3 weeks.