Detection of intracellular lipocortin 1 in human leukocyte subsets

Lipocortin 1, a putative mediator of the antiinflammatory actions of glucocorticoids, is present intracellularly in a variety of tissues including human peripheral blood leukocytes. We investigated the presence of lipocortin 1 in human leukocyte subsets using permeabilization flow cytometry. Constitutive lipocortin 1 was detected in U937 myelomonocytic leukemia cells, and lipocortin 1 was increased by treatment with PMA or PMA + IFN-γ (P < 0.05) but not by dexamethasone. Lipocortin 1 was present in all leukocyte subsets except B lymphocytes (CD19/20⁺, P < 0.001). Lipocortin 1 content was maximal in monocytes and polymorphonuclear neutrophils and least in lymphocytes (P < 0.001). Monocyte lipocortin 1 was strongly associated with surface expression of CD14 and HLA-DR. Among non-B lymphocytes, a range of lipocortin 1 fluorescence was observed. Lipocortin 1 fluorescence was greatest in natural killer cells (CD56+, P < 0.001) and CD57⁺ cells, but T cell subset markers did not otherwise discriminate variations in lipocortin 1. Induction of lymphocyte proliferation by PHA, anti-CD3, Con 4 superantigen, and SAC was not associated with significant shifts in lipocortin 1 content. Dexamethasone (10^-10-10^-6 M) did not induce increases in PB leukocyte lipocortin 1. We conclude that lipocortin 1 content in human leukocytes varies significantly among phenotypic subsets. This has significance for the investigation of inflammatory disease where certain cell types predominate.