Objectives: To characterize ELFs in the SJL EAE mouse model and to correlate with clinical information.
Methods: Eight female SJL mice were injected subcutaneously with (0.2 mg/mouse) PLP 139–151 peptide (HCLGKWLGHPDKF) in complete Freund’s adjuvant on days 0 and 7, and with pertussis toxin (0.2 µg/mouse) intraperitoneally on days 0, 1, 7 and 8. Clinical disease scores were recorded daily. Four mice were sacrificed at 5 weeks, and four at 15 weeks. Sections of brain and spinal cord were immunostained for B cells (B220; BD Pharmingen), T cells (CD3; Santa Cruz), and follicular dendritic cells (CXCL13; R&D Systems). Spleen was used as a positive control. Sections from two animals were also stained for myelin proteolipid protein (PLP; Serotec) to detect areas of demyelination. Groups of ≥ 5 B220 cells defined clusters. Clusters were classified as ELFs if they contained CXCL13 expressing cells. Clusters and ELFs, along with the numbers of B cells, T cells, and CXCL13+dendritic cells within each, were enumerated.
Results: Six of eight EAE-affected mice displayed ELFs. The two that did not were both sacrificed at the earlier time point of 5 weeks, although each had relapsed. Conversely, ELFs were identified in all four mice sacrificed at 15 weeks including the two mice that did not relapse. Although B cell clusters could be detected intraparenchymally, ELFs were seen only in the meninges or around superficial vessels of the brainstem. A few ELFs were also seen in the spinal cord meninges. Using PLP staining to detect myelin, no demyelination was observed near ELFs. When observed, CXCL13 was identified within B cell aggregations, but not all B cell clusters represented ELFs. More T cells than B cells were present within clusters and ELFs.
Conclusions: We confirmed the development of ELFs in the SJL mouse model of EAE. Based on a limited sample, ELFs appeared to require chronic disease of many weeks for development. ELFs appeared to have a predilection for the ventral meninges of the brainstem, consistent with a previous report. Future work with expanded numbers of mice and further characterization is planned.