Neutrophil depletion affects Dark Agouti Experimental Autoimmune Encephalomyelitis

Objective: Neutrophils have been shown to own several immunoregulatory properties. Nevertheless few attention has been given to their contribution to both Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis (EAE) etiopathogenesis and progression. We aim to investigate the potential role of neutrophils during EAE sensitization and chronic phase in Dark Agouti (DA) EAE. Methods: Chronic EAE was induced in DA rats by intrafootpad injection of syngenic spinal cord homogenate in incomplete Freund's adjuvant. Neutrophils were depleted by means of intraperitoneal injection of anti-rat neutrophil serum (aNEU) at different disease time course, i.e. either during the sensitization and the chronic phase of the disease. The animals were weighted weekly and aNEU effect was first evaluated on clinical score while deeper analysis were performed on blood formula, spleen morphology and spinal cord cytokine, chemokine and myelin basic protein expression. Results: aNEU had no effect on clinical score when neutrophil depletion was performed during the chronic phase, i.e. from 14 to 35 days post EAE induction (dpi). When aNEU was administered during the EAE sensitization phase up to 8dpi, no difference in mean clinical score could be revealed between EAE and aNEU-treated EAE rats up to the disease peak, i.e. 14 dpi. However a significant improvement in clinical condition could be reported soon after the disease peak so that a chronic course was transformed into an acute/ monophasic one. aNEU treatment induced a faster body weight gain while it did not affect blood formula changes related to EAE course. Moreover while aNEU treatment did not counteract EAE effects on both spleen microscopic morphological changes and Treg (FoxP3) content, it mainly affected the expression of both pro- and anti-inflammatory cytokines in the three main spinal cord traits (cervical, thoracic, lumbar) while relative low effect was observed on both MCP-1 and myelin basic protein expression. Conclusions: Neutrophil depletion transformed a chronic EAE model into an acute/monophasic one and resulted in cytokine expression changes in spinal cord mainly referred to the cervical trait. Acknowledgment: This project was supported by FISM — Fondazione Italiana Sclerosi Multipla cod 2009/R/22. We wish to thank Mr. Oggioni for his support in animal management.