The hematopoietic form of Slp2a interacts with Rab27a in transfected 293T cells and in primary T cells. (A) The TAP-active (TAP-Rab27aQ) or TAP-inactive form of Rab27a (TAP-Rab27aT) was cotransfected in 293T cells with the hematopoietic form of Slp2a. Cell lysates were immunoprecipitated with IgG beads. Coprecipitated Rab27a TAP mutants and Slp2a-hem were examined using immunoblot analysis with anti-Rab27a and anti-Slp2a. (B) Primary CTLs (LAK-T Co) from a control patient and a GS2 patient 1 (LAK-T P1) were lysed in the presence of phosphatase inhibitors. Cell lysates were immunoprecipitated with the beads alone (LAK-T beads) or with a monoclonal anti-Rab27a. The immunoblots were analyzed using anti-Rab27a, anti-Slp2a, and anti–Munc13-4. (C) Total cell lysates of primary CTLs from a control (Lak-T Co) and a GS2 patient with Rab27a nonsense mutation (Lak-T P2) analyzed by Western blotting. Blot was probed with anti-Rab27a and anti-Slp2a. Western blot analysis of PI3K was used as a loading control. (D) RT-PCR analysis of Slp2a-hem–specific transcript from a control and GS2 patient P2 (Lak-T P2). Actin expression was used for normalization.