Immunoglobulin sub-class levels define inter-donor plasma variability: a longitudinal dual-lab study.

Advances in mass spectrometry have transformed plasma proteomics, allowing high-throughput analysis of large cohorts. This study utilized the TIMES (Tracking Individuals Monthly for Evaluating Stability) cohort, consisting of 51 healthy participants monitored monthly over 12 months, to evaluate intra- and inter-individual variability in the plasma proteome. Approximately 600 samples were analyzed in two laboratories independently, revealing strong correlations despite methodological differences. The study revealed high stability of the plasma proteome within donors over a year, with larger differences observed between donors. A support vector machine model achieved a 98% median classification accuracy, confirming stable, donor-specific proteomic profiles. Immunoglobulins, often overlooked in plasma proteomics, were found to contribute significantly to donor-specific signatures, showing pronounced inter-individual variability but remarkable intra-donor stability. In contrast, C-reactive protein and other inflammation markers exhibited significant temporal fluctuations from donor-specific baseline levels. This inter-laboratory study highlights the importance of longitudinal sampling for biomarker discovery, the robustness of MS-based proteomic workflows, and provides new insights into immunoglobulin dynamics and variability in human plasma.