APS, primary antiphospholipid syndrome; AUC, area under the curve; Ab, autoantibody; Autoantibodies; Autoimmune diseases; CCP, cyclic citrulinated peptide; CXCL10, C-X-C motif chemokine 10; F, female; FLC, free light chains; Free light chains; HC, healthy controls; IFN, interferon; Interferon signature; M, male; MCTD, mixed connective tissue disease; MDA, malondialdehyde; NK, natural killer; PC, phosphorylcholine; RA, rheumatoid arthritis; RF, rheumatoid factor; RNP, ribonucleoprotein; ROC, Receiver Operating Characteristics; SAD, systemic autoimmune diseases; SD, standard deviation; SLE, systemic lupus erythematosus; Scl, systemic sclerosis; SjS, Sjögren's syndrome; TH1, T helper type 1; TNF-R1, tumor necrosis factor receptor 1; UCTD, undetermined connective tissue disease; VAS, visual analogical scale; κ, kappa; λ, lambda