Identification of specific proteins in different lymphocyte populations by proteomic tools

The solubilized proteins of purified CD19+ (B), CD8+ (T) as well as CD4+ (T) lymphocytes were separated by high resolution two‐dimensional polyacrylamide gel electrophoresis, and the gels were analyzed using Melanie 3.0. Nine gels were studied, three for each lymphocyte population. After image analysis, 1411 ± 73 spots (mean + SD) were detected. The protein pattern of B lymphocytes segregated from the one of T lymphocytes by ascendant heuristic clustering analysis. In addition, computer analysis separated CD8+ from CD4+ lymphocytes. When a search was performed in order to detect subsets of specific spots (presence vs. absence), a group of three spots, detected in the area of the protein maps corresponding to isoelectric point (pI) of 5.2 to 5.4 and molecular weight (Mr) of 50 to 51 kDa, were found in both CD8+ and CD4+ cells, but not in CD19+ cells. Mass spectrometry analysis revealed that these spots were associated with several proteins such as vimentin, tubulin, desmin and cytokeratin. Two spots, located in the area of the gel corresponding to pI of about 5.0 and a Mr of 30 kDa, appeared as CD8+ cell associated. Mass spectrometry analysis showed that the two spots were related to the same non‐identified protein. Moreover internal peptides sequences matched with two human expressed sequence tags: gi|9759776, gi|12798420. No spots were found as only B cell associated.