AB0142 Immunosuppressive effects of glucocorticoids and regulatory t cells on cd28null t cells in vitro
Authors: J. M. Pandya, M. S. Hossain, I. E. Lundberg, V. Malmström
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> CD28null T cells are terminally differentiated T cells lacking CD28 co-receptor. These cells display properties of proinflammatory killer cells<sup>1, 2</sup> and are suggested to be resistant to apoptosis <i>in vivo</i><sup>3</sup>. Frequencies of CD28null T cells are increased in various chronic, inflammatory diseases. CD28null T cells dominate both in the affected muscle and peripheral blood of patients with idiopathic inflammatory myopathies<sup>2, 4</sup> (myositis), suggesting a role these cells in disease mechanism and muscle pathology. Recently, it was found in our lab that after conventional glucocorticoid treatment, the relative number of regulatory T cells (Tregs) was unchanged or decreased, while the CD28null T cell proportion was mainly increased in muscle tissue of myositis patients (unpublished data). This leads to our working hypothesis that CD28null T cells are resistant to immunosuppression mediated by glucocorticoids in the setting of myositis. Such resistance could also be against Tregs mediated immunosuppression due to distinct phenotype of CD28null T cells. <h3>Objectives</h3> The aim of this study was to evaluate the immunosuppressive effects of glucocorticoids and Tregs on CD28null T cells in an <i>in vitro</i> system. <h3>Methods</h3> Peripheral blood mononuclear cells (PBMCs) were obtained from 3 healthy individuals using Ficoll separation. CD3+CD4+CD25++(high) cells were sorted as Tregs by flow cytometry. For glucocorticoid or Tregs mediated T cell suppression assays, PBMCs were stimulated with plate bound α-CD3 antibody in presence of 4uM glucocorticoid (methyl prednisolone sodium succinate) or optimal proportion of Tregs. Up-regulation of the early activation marker CD69 was measured by flow cytometry. Suppression was estimated based on % reduction in CD69 mean fluorescent intensity compared to stimulated control cells. <h3>Results</h3> CD4+CD28null T cells (median % suppression: 40.1%) displayed lower sensitivity towards glucocorticoid-mediated suppression compared to CD28+ counterparts (median: 54.7%), seen in all individuals tested. Similarly, CD4+CD28null T cells (median: 17.5%) were less sensitive towards Tregs mediated suppression compared to CD28+ counterparts (median: 34.4%) in all individuals. No clear trend could be observed in CD8 compartment so far. <h3>Conclusions</h3> Although, more individuals need to be tested, the above <i>in vitro</i> data support our <i>in vivo</i> findings that CD28null T cells are relatively resistant to glucocorticoid and Tregs mediated immunosuppression. Lower sensitivity of CD28null T cells towards glucocorticoid and Tregs mediated suppression support their treatment resistance nature in myositis and a role in chronic inflammation and autoimmunity. <h3>References</h3> Fasth, A. E. et al. Arthritis Res Ther (2007), 9, R87, 2286. Pandya, J. M. <i>et al.</i><i>Arthritis Rheum</i> (2010). <b>62</b>, 3457-3466. Schirmer, M. et al. J Immunol (1998) 161, 1018-1025. Fasth AE, et al. J Immunol. (2009) Oct 1;183(7):4792-9. <h3>Disclosure of Interest</h3> None Declared