Antiribosomal P protein antibodies in cerebrospinal fluid are associated with neuropsychiatric systemic lupus erythematosus.

OBJECTIVE: To investigate whether antiribosomal P protein antibodies (anti-P) are present in the cerebrospinal fluid (CSF) of patients with systemic lupus erythematosus (SLE), and if presence of anti-P in CSF is more strongly related to the appearance of neuropsychiatric SLE (NPSLE) than anti-P in serum.
METHODS: CSF and serum samples from 70 patients with SLE were used. Patients were divided into 4 groups: 21 patients with neurologic syndromes of the central nervous system (CNS); 19 patients with diffuse psychiatric/neuropsychological syndromes; 10 patients with complex presentations (neurologic syndromes of the CNS plus diffuse psychiatric/neuropsychological syndromes); and 20 patients without NPSLE based on diagnostic criteria for 19 NPSLE syndromes proposed by the American College of Rheumatology. IgG anti-P in CSF and serum samples were detected by Western blotting using rat liver ribosomes. Inhibition assay was performed using 5 anti-P-positive CSF samples preincubated with synthetic ribosomal P peptide. Western blotting results were compared with those from ELISA with synthetic ribosomal P peptide as antigen. The association of CSF and serum anti-P with NPSLE was analyzed.
RESULTS: CSF and serum IgG anti-P by Western blotting were detected, respectively, in 20 (28.6%) and 32 (45.7%) of 70 patients. The presence of IgG anti-P by Western blotting in the CSF was supported by positive results in the inhibition assay and significant association with CSF IgG anti-P titers by ELISA. The frequency of CSF anti-P by Western blotting in SLE patients with serum anti-P was significantly higher than in SLE patients without serum anti-P (18/32 vs 2/38; p < 0.001). The frequency of CSF anti-P by Western blotting in patients with NPSLE was significantly higher than in patients without NPSLE (19/50 vs 1/20; p < 0.01). The frequency of CSF anti-P by Western blotting in the group with complex presentations (10/10) was significantly higher than in the other 3 groups [neurologic syndromes of CNS (5/21); diffuse psychiatric/neuropsychological syndromes (4/19); and patients without NPSLE (1/20)] (p < 0.001). The frequency of serum anti-P by Western blotting in patients with NPSLE was not significantly higher than in patients without NPSLE (25/50 vs 7/20; p = 0.192).
CONCLUSION: These results suggest that the presence of IgG anti-P in CSF of SLE patients may be involved in the appearance of NPSLE, especially in complex presentations. Measurement of IgG anti-P in CSF by Western blotting may be more useful for diagnosis of NPSLE than measurements in serum.