LYMPHATIC TISSUE CHANGES IN RATS FLOWN ON SPACELAB-LIFE-SCIENCES-2

Thymus, spleen, inguinal lymph node, and bone marrow specimens from ra ts flown on the 14-day Spacelab Life Sciences-2 mission were Examined after staining of tissue sections. The primary observation was a trans ient retrogressive change in lymphatic tissues in the rats within a fe w hours after landing. There was a diffuse increase in tingible body-c ontaining macrophages in the cortex of the thymus, thymus-dependent ar eas of the splenic white pulp, and inguinal lymph node. This was not o bserved 9 days after recovery. The in situ labeling of fragmented DNA strands catalyzed by exogenous terminal deoxynucleotidyltransferase (T dT) with ApopTag reagents (Oncor, Gaithersburg, MD) inside the tingibl e body-containing macrophages indicated that tile process was one of a poptosis. No increase in tingible body macrophage activity was noted i n thymus and spleen tissue obtained from rats in flight on flight day 13. The reaction to gravitational stress from readaptation to 1 G is t he most likely explanation of the transient retrogressive change in ly mphatic tissues.