Antisyntaxin 2 and 4 antibodies inhibit lysosome secretion.

Panel A: SLO-permeabilized platelets were incubated with increasing amounts of antibodies against syntaxin 2 (pp2), 4, 7, and a nonspecific rabbit IgG (0-0.24 mg/mL). The release of hexosaminidase was measured and normalized to the control (buffer alone). Panel B: SLO permeabilized platelets were incubated on ice for 30 minutes with buffer (control), or with 30 μg/mL antisyntaxin 2 antibody (pp2) or 50 μg/mL antisyntaxin 4 antibody alone or after preincubation with either recombinant syntaxin 2 (200 μg/mL) or syntaxin 4 (200 μg/mL) as indicated. Permeabilized platelets were also incubated on ice with the recombinant syntaxins (2 and 4), preimmune rabbit IgG, or a combination of antisyntaxin 2 and 4 antibodies (30 μg/mL pp2 and 50 μg/mL antisyntaxin 4). Platelets were activated with 10 μmol/L Ca⁺⁺ and the release of hexosaminidase was measured and normalized to the control group.