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Human lymphocytes stored at 4 C either as leukocyte concentrates (LCs) in citrate-phosphate-dextrose (CPD) or as whole blood anticoagulated with CPD show a rapid and marked decrease in the relative and absolute numbers of thymus derived (T) lymphocytes. Determinations were made on cells recoverable on a Ficoll-Hypaque (F-H) gradient. In evacuated LCs, the relative percentage of T cells dropped to less than 10 per cent within 72 hours with a concomitant increase in the relative percentage of bone marrow derived (B) cells to 80 per cent or more. LCs opened to the air and subsequently stored at 4 C displayed an even more precipitous decline in the relative percentage of T cells, reaching a 10 per cent level within 72 hours. The relative percentage of T cells in CPD-anticoagulated whole blood samples stored at 4 C displayed similar decreases, reaching 20 per cent levels within 24 hours. The change in the relative percentage of T cells at the Ficoll-Hypaque interface was shown to reflect a decrease in the total numbers of T cells placed on the F-H gradient with time, since determinations of T and B cell numbers in NH4Cl-treated whole blood showed a 65 to 80 per cent decrease in the numbers of T cells within 24 hours in anticoagulated whole blood held at 4 C. Thus, it may be inferred that the T cell decrease is mediated via some interaction of anticoagulant, storage time, and some component(s) present in both LCs and whole blood.

The exposure of mosquito larvae (Aedes aegypti L.) to LC(50) concentrations of DDT for various periods of time resulted in a selective increase in the alanine level of a DDT-resistant strain after 4 to 8 hours' contact with the insecticide, whereas the concentration of this amino acid in a susceptible strain remained comparatively low.