Rolipram, a phosphodiesterase type 4 inhibitor, can markedly down-regulate antigen-driven T cell proliferation and suppress TNF-α production in vitro and in vivo. Here we report the effects of Rolipram on experimental autoimmune neuritis (EAN), which can be induced by immunization with myelin components of the peripheral nervous system (PNS) combined with Freund's complete adjuvant (FCA), and which represents a CD4+ T cell-mediated animal model for human Guillain-Barré syndrome. EAN induced in Lewis rats by inoculation with the PNS P2 protein peptide 57–81 and FCA was strongly suppressed by Rolipram administered twice daily intraperitoneally from day 9 post immunization (p.i.), i.e. after onset of clinical EAN. Suppression of EAN was associated with down-regulated myelin antigen-induced T cell responses as well as down-regulated IFN-γ and TNF-α production. A relapse of clinical EAN occurred upon treatment of a short duration (7 days), while prolongation of treatment resulted in the prevention of clinical EAN relapse. There was no relationship between clinical EAN relapse and high levels of TNF-α. The immunomodulatory effects of Rolipram call for further research into the potential role of drugs acting on the immune system in the treatment of autoimmune diseases.

Interleukin‐6 (IL‐6) is a multifunctional cytokine with a broad range of activities and can affect a variety of target cells or systems in multiple ways. However, there is currently no consensus on how IL‐6 directly affects the peripheral nervous tissue. We performed histopathological and immunohistochemical analyses to investigate the direct effects of recombinant rat IL‐6 (rrIL‐6) following its intraneural injection into the sciatic nerve of adult Lewis rats. One day after injection, a large number of macrophages, major histocompatibility complex (MHC) class II positive cells, and CD4+ and CD8+ T cells appeared within the perineurium and endoneurium. From day 4 to day 7 after injection, we observed a gradual increase of inflammation and demyelination. On day 7, demyelination affected more than 80% of nerve fibres. In contrast, in the sterile phosphate‐buffered saline (PBS)‐injected control group, lower inflammation and fewer demyelinating nerve fibres were observed on days 4 and 7. Thus, intraneural injection of rrIL‐6 into the sciatic nerve induces high inflammation and severe demyelination. This study improves our understanding of the effector mechanisms underlying inflammation and demyelination and identifies IL‐6 as an essential mediator of inflammation and demyelination in the peripheral nervous system after local administration.

Inflammatory cytokines appear to be involved in damage to Schwann cells, myelin and axons, although the exact role of the different cytokines is uncertain. The direct injection model offers a new and simplified way of examining the mechanisms of early inflammation in the peripheral nervous system. The present study was performed to assess the direct effects of interleukin (IL)‐12 on rat sciatic nerves injected with recombinant mouse IL‐12. Histological and immunohistochemical examination 24 h after injection showed early inflammation as well as demyelination within the injected nerve fibres. By 4 days the inflammatory and demyelinating changes were significantly increased. Seven days after injection, the endoneurium still contained significant numbers of inflammatory cells and the demyelination was even more severe. Control rats injected with sterile phosphate‐buffered saline exhibited no such inflammatory and demyelinating response. These changes are similar to those seen in inflammatory and demyelinating disorders of the peripheral nervous system and suggest that IL‐12 could be relevant to the pathogenesis of demyelinating diseases such as Guillain–Barré syndrome.

Experimental autoimmune neuritis (EAN) is a CD4+ T‐cell‐mediated demyelinating disease of the peripheral nervous system (PNS) and serves as experimental model for human immune‐demyelinating neurophathies, especially the Guillain–Barré syndrome. In this study, we examined the effect of recombinant rat interleukin‐6 (rrIL‐6) on chronic EAN in Lewis rats induced by immunization with P2 peptide 57‐81 and Freund’s complete adjuvant (FCA). Nasal administration of rat rIL‐6 (1 μg/rat/day) beginning in the initial phase of EAN as a therapeutic agent, decreased the severity and the duration of clinical EAN. Low‐grade inflammation and suppression of regional demyelination within the sciatic nerves were seen in rrIL‐6‐treated rats. Hyporesponsiveness of lymph node T cells, down‐regulation of serum tumour necrosis factor‐α (TNF‐α) and increased levels of P2‐specific immunoglobulin G1 (IgG1) antibodies document that nasal administration of rrIL‐6 was effective systemically. However, because of the non‐specific nature of the treatment and multiple effects of IL‐6, more experience and great caution are needed, before nasal administration of IL‐6 can be considered as a treatment of human autoimmune demyelinating neurophathies.