This dataset contains peptide identifications derived from immunoprecipitated IgG isolated from mouse serum. Serum samples were obtained from 10 month old Vλ2 315m⁺/⁻ TCR TG⁺/⁻ mice, representing the experimental cohort used to study Ig repertoire composition. A recombinant human IgG3 (hIgG3) expressing mouse VH+VL of interest was processed in parallel and used as a positive control.