PLS1 and periodontitis: In this study, there also were some proteins decreased or absent in SS samples and in common only in periodontitis cases (OP and NP groups), for instance, ATP-dependent RNA helicase DDX55; 12 isoforms of Immunoglobulin (Immunoglobulin heavy constant mu, Immunoglobulin heavy variable 3-23, 3-30, 3-30-3, 3-30-5, 3-33, 3-53, 3-66, 3-74, Immunoglobulin kappa variable 3-11, 3D-11, Immunoglobulin mu heavy chain); Mucin-2; Plastin-1; and Submaxillary gland androgen-regulated protein 3B (Tables S1 and S3).