Zn²⁺-dependent activation of β₂-integrins and adhesion to endothelial cells. (A) Human myelomonocytic HL60 cells were incubated in the absence or presence of 100 μmol/L Zn²⁺ for 20 minutes at room temperature, and surface expression of an activation-dependent epitope (MoAb 24) on β₂-subunit was quantitated by fluorescence-activated cell sorter (FACS) analysis (filled curves). For comparison, quantitative cell surface expression of β₂-subunit was analyzed using MoAb 2LPM19c, which recognizes an epitope irrespective of the activation state of the integrin. Nonspecific fluorescence was determined using an isotype-matched mouse-IgG (open curves). The figure shows one of three representative experiments. (B) Differentiated HL60 cells, preincubated for 30 minutes in the absence or the presence of 100 μmol/L Zn²⁺, 0.5 mmol/L Mn²⁺, or 10 ng/mL PMA as indicated, were allowed to adhere to confluent endothelial cell monolayers in the absence (▩) or presence (▨) of MoAb 60.3 against β₂-integrin. Data represent the mean ± SD (n = 3) of a typical experiment. Similar results were obtained in three separate experiments.