Impairment of splenic B and T lymphocytes in the early period after severe thermal injury: immunohistochemical and electron microscopic analysis.

Immunocompetent cells, such as lymphocytes and macrophages are easily damaged after severe thermal injury. In the present study, we investigated structural changes in splenic lymphocytes in the early period after a full skin thickness burn of 30% of the body surface area in rats. At 2h after thermal injury, numerous B lymphocytes had accumulated in the markedly expanded marginal zone of the splenic white pulp. Electron microscopy showed a small number of apoptotic cells in the marginal zone of the white pulp. After 5h, B lymphocytes in the marginal zone as well as in the lymphoid sheath and follicles were markedly decreased in number with an increase of tingible bodies and tingible body macrophages. The number of apoptotic cells had increased not only in the marginal zone, but also in the lymphoid sheath and follicles. After 12h, the splenic white pulp became atrophic with the appearance of a small number of large blastic cells and mitotic figures. After 24h, the splenic white pulp was still atrophic with a decrease in the number of lymphocytes, especially B lymphocytes. On the other hand, the large blastic cells and mitotic figures increased in number. Apoptotic cells decreased in number in the white pulp. After 48h, the lymph follicles were slightly enlarged and a small germinal centre occasionally appeared. A small number of T lymphocytes were observed in the splenic white pulp of the normal rats. However, the T lymphocytes almost disappeared shortly after thermal injury. A recovery in T cell number was observed only after 48h. These findings indicate that severe impairment of both B and T lymphocytes, circulating and in the lymphoid organs, occurs shortly after thermal injury and continues for several days. This severe damage to the lymphocytes is considered to be closely related to severe immune suppression after thermal injury.