| Objective: To explore the dynamic changes of T lymphocyte in spleen and thymus in hyperoxic lung injury in newborn rats.Methods: 72 newborn SD rats were randomly assigned to a hyperoxic group and a control group ( n = 36 each). The hyperoxic group was exposed to high concentration of oxygen ( FiO2 0.800.85) and induced hyperoxic lung injury. The control group was exposed to room air ( FiO2 = 0.21). The rats were randomly subdivided into groups sacrificed at 1, 4, 7, 14 and 21 days of exposure respectively. Lung tissues were collected and made into 5μm sections and analyzed by histopathologic method. Ratio of CD4+,CD8+ lymphocyte subsets in spleen was measured by flow cytometer(FCM). Functional analysis was performed with "mixed lymphocyte reaction" of splenocyte responder cells with PHA and autologous lung cells as the stimulators. Thymus tissues were collected and made into 5μm sections and analyzed by histopathology. The expression of proliferating cell nuclear antigen (PCNA) and the distribution of CD4+,CD8+ in the tissues was detected by immunohistochemistry.Results: (1).pathological changes of lung tissue. On the 4th day, the pathological findings show congestion, edema in the lung tissue after hyperoxic exposure. After 7 days, compared with control group, inflammatory infiltration was observed besides of the continuous edema. On the 14th day, inflammatory reactions were lighten in the lung tissue, but the interstitium were widen and the fibrocytes were hyperplastic. On the 21th days, the pathological findings as hyperinflated lung segments alternating with regions of atelectasis and fibrosis, characterized by enlarged alveoli with reduced septation and impaired capillary developed.(2).changes of T lymphocytes in the spleen. On the 4th day, the total quantities of spleen lymphocytes in hyperoxic group were higher than that of the control group. After 7 days of hyperoxic exposure, the ratio of CD4+ and CD8+ were significantly higher than that of control groups(P<0.01,respectively). After that the ratio of CD4+ and CD8+ decreased gradually at 14th days. On the 21th day, the ratio and the total quantitives of CD8+lymphocyte were significantly lower than that of control group (P<0.01,respectively). Moreover, from 4th to 7th day, the response of CD4+ lymphocyte to autologous lung cells and PHA were significantly higher than that of control groups (P<0.01,respectively). On the 14th day, the activities of lymphocyte to PHA decreased. After 21 days of hyperoxic exposure, activities of splenocyte responder cells with PHA as the stimulators declined progressively compared to control groups. (P<0.01).(3).changes of T lymphocyte in the thymus.From the 4th to the 7th day of hyperoxic exposure, on routine slide review, both of the index of thymus and PCNA were higher than that of control groups, but decreased gradually from the 14th to the 21th day, and the index of PCNA was significantly lower than that of control group on the 21th day(P<0.01). On the other hand, pathological findings showed the decreased quantities of the CD4+ and CD8+ and distributed regionally.Conclusion: (1).Exposure of newborn rats to 8085% oxygen impairs lung growth as characterized by decreased alveoliar numbers with reduced septation and impaired capillary development, which is similar to the neonatal chronic lung injury.(2).The quantities and activities of CD4+ and CD8+ in the spleen significantly increase in early period of hyperoxic lung injury and significantly decreased lately.(3.)Hyperoxic lung injury may induce the thymus of newborn rats pathological from accelerated maturation to pathological atrophy, which represent in slide that quantities the CD4+ and CD8+ decreased and distributed regionally.(4).The autoreactive T cells participating in the process of hyperoxic lung injury could be due to accelerated thymus maturation.(5).Decline of immunity of organism following hyperoxic exposure may be associated with the abnormal development of thymus and the derangement of quantity and function of lymphocyte.
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