AL 721: a potent membrane modulating agent of human T-lymphocytes?

This report deals with AL 721, a reputedly potent membrane fluidizing agent. A correlation has been sought between the effects of AL 721 on membrane fluidity and mitogen responsiveness of human peripheral blood lymphocytes. The AL 721-induced increase in membrane "fluidity", as measured by fluorescence polarisation with 1,6-diphenyl-1,3,5-hexatriene, was found to be an artefact arising from lipid uptake by monocytes. Mitogen responses were enhanced by inclusion of AL 721 in the serum-free culture medium. However, this observation is more likely explained by provision of lymphocytes with nutritional lipids required for optimal growth in vitro, than altered responsiveness of "fluidized" lymphocytes.