Regulational expression of the CD28-related costimulatory molecule ICOS in Multiple Sclerosis : implications for the role of costimulation in autoimmunity

Costimulatory signals play a key role in regulating T cell activation and are believed to have decisive influence in the inciting and perpetuating cellular effector mechanisms in autoimmune diseases such as multiple sclerosis (MS). Inducible costimulator protein (ICOS), a recently identified member of the CD28-family, presumably affects the differentiation of Th1/Th2 cells after primary activation and modulates the immune response of effector/memory T cells. This study examined the constitutive expression as well as upregulated expression after antigen-specific stimulation of ICOS and the cytokines IL-4, IL- 10 and IFN-g in healthy donors and patients with MS. Gene-expression of these molecules and numerous B7-costimulatory molecules was also examined in brain tissue specimen from a patient with MS as well as in antigen presenting cells. Additionally ICOS expression in CD4+CD25+ cells and in Th1 and Th2 specific T cell lines was examined. For this purpose techniques such as flow cytometry and QRT-PCR were used. Furthermore the question whether QRTPCR is an appropriate approach to detect changes in the gene expression profile in low frequencies of autoreactive T cells was addressed. Analysis of ICOS gene-expression in Th1 and Th2 specific T cell lines clearly revealed ICOS gene expression being restricted to Th2 specific cells whereas it was absent in Th1 specific cell lines. Comparison of constitutive cell surface expression and upregulational kinetics of ICOS on CD4+- and CD8+-T cells showed no differences in patients with MS and healthy individuals. It was furthermore shown that ICOS is not exclusively expressed in CD4+CD25+ cells and thus is not a marker for this regulatory subset. Gene expression of ICOS, IL-4, IL-10 and IFN-g in PBMCs after antigen specific stimulation in MS patients and healthy individuals differed for IL-4 and IL-10 after stimulation with MBP84-99 and MOG, respectively. IL-4 expression was higher in healthy individuals, whereas greater IL-10 expression was detected in MS patients. However, as these two Th2 cytokines were upregulated in MS patients and healthy individuals in an opposing way, no conclusions with respect to their role and the role of ICOS in the pathogenesis of MS can be drawn. With regard to the expression of B7-costimulatory molecules in APC it is not surprising that the greatest amounts of gene expression was found in mature DC as these cells are the most potent APC. Some interesting findings could also be made for the gene-expression of ICOS and other costimulatory molecules in tissue specimen from a patient with MS: In one human brain specimen classified as “normal appearing white matter” upregulated gene expression of ICOS, other B7 costimulatory molecules and of inflammatory cytokines could be detected whereas in other specimen also classified as “normal appearing white matter” only moderate levels of these molecules could be found. This noteworthy observation indicates that in CNS of MS patients inflammatory activity is potentially present in histopathologically normal appearing areas. With regard to the applicability of QRT-PCR to detect changes in the gene expression profile of autoreactive T cells it was found that the method is useful as long as frequencies of the cells are higher as the elucidated detection threshold.

Author

• Mehling, Matthias

Identifier

hdl:10900/44771

OAI record oai:identifier

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