Background Rheumatoid arthritis (RA) has recently been linked to an exhausted state of CD4⁺ T cells in peripheral blood of patients [1]. Exhaustion of CD4⁺ T cells limits their proliferation and increases cell death. In CD8⁺ T cells smoking counteract exhaustion, which may lead to increased cytotoxic activity exemplified by targeting of cells with high expression of the anti-apoptotic protein survivin [2]. Exhaustion of CD4⁺ T cells coincides with expression of interferon (IFN) response genes [3], referred to as the IFN signature. The development of the IFN signature has been suggested to predate RA [4].

Objectives We investigated how smoking affect the CD4⁺ T cell population in peripheral blood of RA patients with focus on the exhaustion marker programmed cell death-1 (PD-1).

Methods Blood samples were collected from RA patients and healthy women with different smoking status and analysed for PD-1 and survivin expression using flow cytometry and qPCR. Sorted Th17 cells from peripheral blood were analysed for expression of 18 genes up regulated during exhaustion [3], herein referred to as the exhaustion set, and serum levels of survivin were assessed by ELISA. Peripheral blood CD4+ cells were analysed for their expression of seven IFN response genes [4]. The role of survivin in the formation of exhausted CD4⁺ T cells was studied in collagen-induced arthritis (CIA), where mice were treated with nicotine or vaccinated with survivin peptides.

Results High frequency of exhausted PD-1⁺CD4⁺ cells was found in smoking RA patients. The numbers of PD1⁺CD4⁺ cells correlated inversely with the PD-1 expression by cytotoxic CD8⁺CD107⁺ cells (r=-0.62, p=0.01). Additionally, the frequency of PD-1⁺CD4⁺ cells increased with reduction of the CD4⁺ population (r=-0.71, p=0.002). The IFN signature was found exclusively among smoking RA patients. The patients with the IFN signature all had CD4⁺ cells with low survivin production. Th17 cells from RA patients with high serum survivin were enriched in genes of the exhaustion set. CD4⁺ cells with high survivin expression were negative for PD-1, while PD-1^hi cells had low expression of survivin. In CIA mice the survivin^hiPD-1^- CD4⁺ cells were reduced by nicotine treatment (p=0.03) or survivin vaccination (p=0.009).

Conclusions Smoking associates with exhaustion of CD4⁺ T cells in RA by increasing the frequency of PD-1⁺CD4⁺ cells and supporting the IFN signature. Balancing T cell exhaustion and preventing the IFN signature are potential future treatment strategies for RA.

References

1. Frenz T, et al. J Allergy Clin Immunol 2016. 138(2): 586–589.

2. Wasén C, et al. J Autoimmun 2017. DOI: 10.1016/j.jaut.2016.12.00.

3. Crawford A, et al. Immunity 2014. 40(2): 289–302.

4. Lübbers J, et al. Ann Rheum Dis 2013. 72(5): 776–780.

References

Disclosure of Interest None declared