Cytokine mRNA expression in inflammatory multiple sclerosis lesions: detection by non-radioactive in situ hybridization.

The predominant pathological features in the central nervous system (CNS) in multiple sclerosis (MS) are perivascular inflammation and demyelination. The cells in the inflammatory cuff consist mainly of T lymphocytes and macrophages. Cytokines produced by inflammatory cells within the CNS have the potential to enhance local inflammation and promote phagocytosis of myelin by macrophages, resulting in demyelination. Resident brain cells, microglia and astrocytes, also produce cytokines after stimulation in vitro. We have applied the technique of non-radioactive in situ hybridization to examine which cells in the CNS are producing cytokines in MS. Using digoxigenin-labelled oligonucleotide probes we have detected expression of the cytokines IL-1 alpha, IL-2, IL-4, IL-6, IL-10, IFN-gamma, TGF beta 1 & 2 and TNF-alpha in frozen sections of CNS tissue from MS cases. The intensity and distribution of the staining for mRNA is cytokine specific, IL-6, IFN-gamma and TNF-alpha predominating in the perivascular inflammatory cuffs, the others being more weakly expressed. Expression of all cytokine mRNAs is stronger in perivascular cells rather than in parenchymal cells, suggesting that circulating inflammatory cells which have crossed the blood brain barrier are the major source of cytokines in MS tissue.