Studies on cytokine mRNA expression in mononuclear cells in neuroimmunological diseases

Abstract

Background: Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS), characterized by perivascular accumulation of blood mononuclear cells (MNC) and patchy demyelination. High levels of circulating myelin antigen specific T and B cells, with an accumulation in cerebrospinal fluid (CSF), suggest the involvement of cytokines in the pathogenesis of MS. Aseptic meningo-encephalitis (AM) may serve as a relevant control for immunological studies for MS since it is an inflammatory disease of the CNS but with a benign and self-limiting course. Myasthenia gravis (MG) is a neuromuscular disorder mediated by autoantibodies against the nicotinic acetylcholine receptor (AChR) on the postsynaptic membrane of the neuromuscular junction. The production of autoantibodies is regulated by T cells by means of immunoregulatory cytokines. The aim of the study was to investigate whether any specific cytokine profile exists in MS or MG and how cytokine profiles may be altered by immunomodulatory treatment.

Materials and method: Blood MNC were obtained from patients with MS, AM, MG, other neurological diseases (OND) and healthy individuals. In parallel, CSF was taken from patients with MS and AM. In situ hybridization with synthetic oligonucleotide probes was used to detect and enumerate MNC expressing LT-a, TNF-a, IL-6, IL-13, IL-12, perforin, IFN-y, TGF-B and IL-10 mRNA. Results are presented as numbers of cytokine mRNA expressing cells per 100.000 MNC. In some studies ELISA was used to detect plasma levels of cytokines IL-12 and IL-13, and soluble vascular cell adhesion molecule-l (sVCAM-I).

Results: Levels of LT-a, TNF-a, IL-6, IL-12, IL-13 and perforin mRNA expressing blood MNC were similar in patients with MS and AM, and higher than in healthy subjects. In CSF compared to paired blood samples from MS and AM patients higher numbers of spontaneously LT-a, TNF-a, IL-6, IL 12, IL-13 and perforin mRNA expressing MNC were detected, reflecting compartmentalized inflammation in both diseases. In contrast to MS, MG was not associated with a general increase in cytokine mRNA expressing cells with the exception for IL-12 which was elevated. Stimulation of blood MNC with MBP or PLP in MS, and AChR in MG resulted in higher numbers of LT-a, TNF-a, IL-6, IL-12, IL-13 and perforin mRNA expressing MNC compared to unstimulated cultures. This was not seen in control patients with AM, OND or healthy subjects. Numbers of organ specific autoantigen reactive cytokine mRNA expressing MNC were also higher in MS and MG compared to controls. In MS, numbers of MBP-reactive LT-a and TNF-a mRNA expressing MNC were also higher in CSF than blood. Levels of MBP-specific TNF-a mRNA expressing CSF MNC correlated with MS exacerbations.

Immunosuppressive drugs decreased numbers of AChR-reactive perforin mRNA expressing MNC in MG, probably reflecting one effector mechanism of immunosuppressive treatment. IFN-Blb treatment of MS patients had little effects on levels of MNC spontaneously expressing cytokine mRNA with the exception of transient increase of MNC expressing TNF-a and perforin, and decrease of IL-10 mRNA expressing MNC. IFN-Blb treatment had no effects on MBP-reactive IFN-y, TNF-a, TGF-B, IL-10 or perforin mRNA expressing MNC, but resulted in higher plasma levels of sVCAM- I .

Conclusions: Similarly upregulated levels of spontaneously LT-a, TNF-a, IL-6, IL-13, IL-12 and perforin mRNA expressing blood and CSF MNC observed in patients with MS and AM suggest that cytokine mRNA expression in MS reflects a non-specific inflammatory process. Correlation of numbers of TNF-a mRNA expressing CSF MNC with MS exacerbations may implicate a disease promoting role for TNF-a. Increased plasma levels of sVCAM-I in MS patients treated with IFN-Blb may reflect the mechanism preventing the migration of autoreactive T cells through the blood-brain barrier.