Analysing gene expression of IFN-ɑ stimulated genes in patients with SLE using direct and indirect methods

Sammanfattning: Systemic Lupus Erythematosus (SLE) is an autoimmune disease where the immune system is attacking the body and its tissues. This leads to a chronic inflammation that can affect different parts of the body and therefore present itself in a vast variety of symptoms. Depending on the activity of the disease it can go up in flares where the patients experience symptoms and then go down into recession. Both the adaptive and innate immune system is involved as well as both genetic and environmental factors. Among other things, it is the formation of autoantibodies, immune complexes and a decreased ability to clear cell debris from apoptotic cells that starts the cascade of events that lead to the chronic inflammation. One important factor in all this is the cytokine interferon alpha (IFN-ɑ) which is mainly produced by plasmacytoid dendritic cells (pDCs) as a response to the cell debris and immune complexes. IFN-ɑ then lower the threshold of B cell receptor (BCR) activation and promote B cell differentiation into autoreactive B cells, as well as promote T-cell activation. This is known as the type I IFN signature that has been observed in patients with SLE. By measuring this signature it would be possible to prevent flares of the disease and to treat the patients with drugs aimed to inhibit the type I IFN system. There is therefore a clinical need for a measuring method that can be used routinely. This study evaluates and compares two different methods to measure the type I IFN signature, one already established a direct method where peripheral blood mononuclear cells (PBMC) are isolated from patient blood samples and the expression of seven different IFN induced genes are analysed. The other method is an indirect method where patient sera is incubated on human epithelial tumor cells (WISH cells) and the same genes are analysed and compared to the PBMC samples. The results were also compared to clinical data and the effect on freezing and thawing RNA and sera was also evaluated. Although there were some coherent samples between the methods the overall result suggests that there is a need for improvement on the indirect method. In regard to freezing and thawing samples, RNA is stable enough for freezing and thawing once but sera is not.