Expression of TLT-1 in platelets. (A) Northern analysis of mRNA isolated from mouse peripheral blood (lane 1) or bone marrow leukocytes (lane 2). Probes are as indicated. (B) Northern analysis of mRNA from mouse dendritic cell cultures (lane 1) and platelets (lane 2). (C) Northern analysis of mRNA from human blood platelets (P, either 5 or 10 μg total RNA loaded), PMNs (N), monocytes (M), or unfractionated PBMCs as indicated. Probes were as indicated. (D) Western blot analysis of lysates from HEK293T cells transfected as indicated immunoblotted with anti–TLT-1. (E) Whole cell lysates from murine peripheral blood leukocytes (PBL), PBLs cleared of platelets (PBL-PLT), bone marrow leukocytes (BM), or enriched platelets (PLT) were immunoblotted with anti–TLT-1 (top) followed by antiactin (bottom). (F) A total of 30 μg whole cell lysate from human (H) or murine (M) platelets was resolved by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE). Quadruplicate filters were probed with either antimurine TLT-1 (left panels) or antihuman TLT-1 (right panels). Antimurine TLT-1 was competed with either human IgG or a fusion protein composed of the extracellular domain of TLT-1 fused to the Fc portion of human IgG. The antihuman immunoblot was competed with PBS or the peptide immunogen. All 4 filters with then washed and bound antibody detected using goat antirabbit IgG coupled to horseradish peroxidase (HRP). The same filters were then stripped and reprobed with antiactin to show loading (bottom panels).