Fig. 2

Elevated IL-6 in MRL/lpr mice correlates with learning and memory dysfunction. A To identify potentially pathogenic molecules in NPSLE, high-throughput proteomic screening of MRL/lpr serum and CSF relative to MRL/mpj samples was performed using RayBiotech 1308-plex mouse protein microarrays. The serum findings (previously published and reproduced here with the permission of the Journal of Autoimmunity) indicated that interleukin-6 (IL-6) is significantly increased in the serum of MRL/lpr mice. B Ten to fifteen CSF samples from either mouse strain were pooled to yield a single 100 µl analyte. This process was repeated twice more, so that protein content of six separate pools (three MRL/lpr and three MRL/mpj) was analyzed using the arrays. A volcano plot is shown, depicting the CSF proteomic array results. Significantly different proteins, including IL-6, are highlighted in red and summarized in the table (left). Of note, neural apoptosis-regulated convertase, GAPDH, and succinic semialdehyde reductase have each been linked to neurotoxicity. Inflammatory cytokines with known roles in human lupus, including IL-3, IL-6, IL-17, MCP-1, and TNF-α, were increased as well (bold, underlined). C Increases in IL-6 previously found on the protein array were validated by measuring IL-6 in the serum of independent cohorts of MRL/mpj vs MRL/lpr mice using ELISA. D–F Using Spearman rank correlations, array-measured serum IL-6 levels from individual MRL/lpr mice were assessed for relationship with performance on object placement (OP, D learning and memory deficits), Porsolt swim (E behavioral despair), and open field (F anxious behavior) tasks. On OP and open field tasks, lower scores were associated with more severe disease. To better represent the correlation between increasing serum IL-6 and worsening disease, the score-based ranks for these tests were plotted in reverse order, with higher ranks representing mice with lower novelty preference/center time (worse performance). *p < 0.05; ***p < 0.0005