Similarity of autoimmune diseases based on the profile of immune complex antigens.

Since immune complexes (IC) are a direct product of immune response through the binding between antigen and antibody, the profile of antigen-associated ICs may depend on each autoimmune disease. In this report, we examined the similarity of four neurological autoimmune diseases, Alzheimer's disease and healthy donors, and seven connective tissue diseases based on the profiling of IC-associated antigens which were previously or recently identified by immune complexome analysis of cerebrospinal fluid (CSF) or serum samples. The similarity between each pair of two diseases was assessed by correlation coefficients as distance matrix with the use of detection frequency (i.e., the percentage of patients who were positive for a certain antigen in each disease) of each IC-associated antigen in a certain disease. Among 15 pairs of five diseases and healthy control examined by the analysis of CSF samples, only 1 pair of neuropsychiatric systemic lupus erythematosus and multiple sclerosis corresponds to the higher correlation value (r = 0.73) than 0.7. On the other hand, among seven connective tissue diseases examined by the analysis of serum samples, 12 of 21 pairs show high correlation value (r > 0.70). Our finding suggested that the profile of IC-associated antigens identified by immune complexome analysis of CSF samples can be useful for evaluating the similarity of neurological autoimmune diseases; however, not by that of serum samples.