Updated FTP location. In this study, we first analyzed the serological repertoire of anti-GM-CSF autoantibodies in a patients serum with autoimmune pulmonary alveolar proteinosis, using the trapped ion mobility spectrometry coupled with quadrupole time-of-flight (timsTOF) Pro mass spectrometry. The timsTOF Pro identified peptides that partially matched sequences in up to 96 percent of cDNA clones. Complementarity-determining region 3 (CDR3), is the most diverse in terms of sequence, was fully and partially detected in nine and 132 clones, respectively. Moreover, we confirmed one unique framework region 4 (FR4) and at least three unique across CDR3 to FR4 peptides via de novo peptide sequencing. This new technology may thus permit the comprehensive identification of polyclonal autoantibody structure.