Anti-MS4a4B antibody recognizes both native and retrovirus-expressed MS4a4B. (A) Western blot of MS4a4B in tissues. Tissue samples from mouse liver, spleen, and thymus were lysed, blotted, and probed with rabbit anti-MS4a4B antibody. Blots were stripped and reprobed with anti-β-actin as a loading control. The position of MS4a4B is shown with an apparent MW of 24 kDa. (B) Lysates from thymus were immunoprecipitated by anti-MS4a4B antibody (or rabbit Ig control)-coated Protein A-Sepharose 4B. The bound proteins were eluted and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and blotted by anti-MS4a4B antibody as described under “Materials and methods.” Expected positions of MS4a4B protein and Ig light chain are shown. The lanes are as follows: (1) total spleen protein (no immunoprecipitation), (2) IP with MS4a4B, (3) IP with control rabbit IgG, (4) MS4a4B IP blocked with MS4a4B immunizing peptide, (5) MS4a4B IP blocked with control MCC peptide. (C) NIH 3T3 cells were infected by MS4a4B retroviral vector or MIGR (empty vector) control. Staining and flow cytometry were performed as described in “Materials and methods.” The results are shown as fluorescence intensity of MS4a4B (solid heavy line) or rabbit IgG control (light line, shaded) in gated GFP⁺ populations. Results shown are representative of 2 experiments.