16/6-idiotype expressing antibodies induce brain inflammation and cognitive impairment in mice: the mosaic of central nervous system involvement in lupus

Abstract

Background: The 16/6-idiotype (16/6-Id) of the human anti-DNA antibody was found to induce experimental lupus in naïve mice, manifested by production of autoantibodies, leukopenia and elevated inflammatory markers, as well as kidney and brain involvement. We assessed behavior and brain pathology of naive mice injected intra-cerebra-ventricularly (ICV) with the 16/6-Id antibody.

Methods: C3H female mice were injected ICV to the right hemisphere with the human 16/6-Id antibody or commercial human IgG antibodies (control). The mice were tested for depression by the forced swimming test (FST), locomotor and explorative activity by the staircase test, and cognitive functions were examined by the novel object recognition and Y-maze tests. Brain slices were stained for inflammatory processes.

Results: 16/6-Id injected mice were cognitively impaired as shown by significant differences in the preference for a new object in the novel object recognition test compared to controls (P = 0.012). Similarly, the preference for spatial novelty in the Y-maze test was significantly higher in the control group compared to the 16/6-Id-injected mice (42% vs. 9%, respectively, P = 0.065). Depression-like behavior and locomotor activity were not significantly different between the16/6-Id-injected and the control mice. Immunohistochemistry analysis revealed an increase in astrocytes and microglial activation in the hippocampus and amygdala, in the 16/6-Id injected group compared to the control.

Conclusions: Passive transfer of 16/6-Id antibodies directly into mice brain resulted in cognitive impairments and histological evidence for brain inflammation. These findings shed additional light on the diverse mosaic pathophysiology of neuropsychiatric lupus.See related Commentary article: http://www.biomedcentral.com/1741-7015/11/91.

Figure 1

16/6-Id injected mice displayed impaired performance in the novel object recognition test. Results are presented as the proportion of time spent near the old and new objects by the 16/6-Id (gray bars) and IgG control (black bars) injected mice. The control mice (IgG) significantly preferred the new object (64% vs. 36% for the proportion time near the new vs. old objects respectively; P = 0.01), while the 16/6-Id injected mice had no significant preference to either objects (56% vs. 44% new vs. old; P = 0.5). Results presented as mean ± SEM. * Statistically significant (P <0.05).

Figure 2

16/6-Id injected mice displayed impaired spatial memory in the Y-maze test. Results are presented as the proportion of time (mean ± SEM) spent in the new arm introduced by the 16/6-Id (gray bars) and IgG control (black bars) injected mice. In the figure it is shown that the control group (IgG injected) spent more time in the new lane as compared to the 16/6 injected group. They have recognized the old lane as known and preferred exploring the new lane, which means that their spatial memory is conserved. There was a significant difference in additional time spent in the new lane between the 16/6 and IgG group (0.46 vs. 0.09, P = 0.02 respectively). * Statistically significant (P <0.05).

Figure 3

Increased brain inflammation (activated microglia) in 16/6-Id mice in the hippocampal regions (CA1, CA3). Staining of activated microglia (green, white arrows) was more prominent in the 16/6-Id injected mice brains (A, C) compared to control mice brains (B, D) in the hippocampal regions CA1 (A, B) and CA3 (C, D). Hoechst nucleus staining – blue, GFAP staining – red. Magnification ×40.

Figure 4

Increased brain inflammation (astrocyes) in 16/6-Id mice in the hippocampal region (CA3). Staining of astrocytes (red) in the hippocampal CA3 region was more prominent in the 16/6-Id injected mice brains (A) compared to control mice injected with commercial IgG (B). Hoechst nucleus staining - blue. Magnification ×40.