CD4 SP thymocytes were sorted and unstimulated or stimulated with α-CD3 mAb and α-CD28 mAb for 16 hours. Cells were washed with PBS and lysed in 150 μl of 6 M guanidine-HCl, 100 mM HEPES-NaOH, pH7.5, 10 mM TCEP, and 40 mM CAA. The lysates were dissolved by heating and sonication, followed by centrifugation at 20,000 × g for 15 min at 4 °C. The supernatants were recovered, and proteins were purified by methanol–chloroform precipitation and solubilized in 20 µl of 8 M urea, 50 mM Tris-HCl, pH8.0. After sonication, the protein solutions were diluted 8-fold with 50 mM Tris-HCl, pH8.0 and digested with 1 µg trypsin/Lys-C mix (Promega) at 37 °C overnight. The resulting peptide solutions were desalted using GL-Tip SDB (GL Sciences), evaporated in a SpeedVac concentrator, and re-dissolved in 0.1% TFA and 3% ACN. LC-MS/MS analysis of the resultant peptides was performed on a nanoElute 2 coupled with a timsTOF HT mass spectrometer (Bruker). The peptides were separated on a 75-μm inner diameter × 150 mm C18 reversed-phase column (Nikkyo Technos) with a linear 5%–35% ACN gradient for 0–60 min followed by an increase to 95% ACN for 1 min and a final hold at 80% ACN for 4 min. Data acquisition was conducted in dia-PASEF mode with an MS1 m/z range of 100–1700 and an ion mobility (1/K0) range of 0.6–1.6. The ramp time was set to 100 ms with a 100% duty cycle. The MS2 polygon was manually defined based on the region where peptides were predominantly detected, specifically using the following four vertices: Point 1 (m/z = 300, 1/K0 = 0.64), Point 2 (m/z = 300, 1/K0 = 0.8), Point 3 (m/z = 770, 1/K0 = 0.97), and Point 4 (m/z = 770, 1/K0 = 1.15). Within the defined polygon, a 8 Da isolation window was employed with an overlap of 0.5 Da for each window, resulting in 62 windows per cycle and a cycle time of 3.36 s. Protein identification was carried out in DIA-NN (version 1.9) against a mouse in silico spectral library. Parameters for constructing the library included: trypsin as the digestion enzyme, one allowed missed cleavage, peptide lengths ranging from 7 to 45 amino acids, precursor charges of 2 to 4, and a fragment ion m/z range of 200–1800. Features such as library-free search, deep learning-based retention time and ion mobility predictions, N-terminal methionine cleavage, and cysteine carbamidomethylation were enabled. In the DIA-NN search settings, MS1 and MS2 mass accuracies were set to auto, neural network classifiers were configured for single-pass mode, and the quantification strategy was set to QuantUMS (high precision).