IGHM and periodontitis: Numerous genes related to immunoglobulin heavy and light change rearrangement and production (IGHG1, IGHM, IGHV2, IGHV3, IGHV4, IGJ, IGKC, IGKV1, IGLV2, IGLV3, and IGLL1) were substantially upregulated with the highest fold increases in aged animals with periodontitis.