Smoking and T cell co-stimulation in rheumatoid arthritis

Abstract

In this thesis I investigated if smoking limits the co-stimulatory system of CD8+ T cells in rheumatoid arthritis (RA). I took special interest in the co-inhibitory receptor PD-1 and its ligand PD-L1. Blood samples from RA patients with known smoking status and experimental models of RA (RA mice) in which orally administered nicotine simulated smoking were used. Additionally, CD8+ T cells were isolated from human blood and stimulated in vitro. Flow cytometry were used to analyze the expression of PD-1. ELISA was used to measure the soluble form of PD-L1 in serum samples from RA patients and healthy controls. Quantitative PCR was used for transcriptional analysis of proteins and microRNAs involved in CD8+ T cell regulation. Microarray analysis of microRNA was performed in samples of human CD8+ T cells. Smokers had fewer activated CD8+ T cells that expressed PD-1 compared to non- smokers, and human CD8+ T cells stimulated with nicotine in vitro had lower expression of PD-1 messengerRNA. RA mice treated with nicotine had fewer PD-1 expressing CD8+ T cells in the bone marrow. This was related to the increased production and release in circulation of the onco-protein survivin, a predictive marker for severe RA. CD8+ T cells of smokers adopted a naïve/memory phenotype and had different expression of several microRNA that are involved in the regulation of memory T cell formation, including the FOXO signaling pathway. Smokers also had lower levels of soluble PD-L1 in serum. The low PD-L1 levels were linked to altered expression of antibody receptors on antigen-presenting cells producing soluble PD-L1. The presence of RA-specific autoantibodies was associated with serum levels of soluble PD-L1. I conclude that smoking interferes with the PD-1 inhibitory system on CD8+ T cells, which may contribute to higher risk for RA in smokers. This can occur because of the reduced inhibitory control of the CD8+ T cells with low PD-1 expression, but also because of a reduced supply of sPD-L1. Furthermore, I suggest that microRNA interfere with the FOXO signaling pathway and influence the phenotype of CD8+ T cells in smokers.