Human CD14+CD16+ intermediate monocytes are expanded in several non-infectious inflammatory conditions. However, their contribution to immune thrombocytopenia (ITP) is less well understood than classical antibody and T cell-mediated autoimmunity against platelets and megakaryocytes. It is nonetheless likely that innate immune cells such as monocytes strongly shape these adaptive immune drivers of ITP, as well as their response to treatment. Given the previously reported impact of systemically administered glucocorticoid (GC) therapy on the proportion and function of CD14+CD16+ intermediate monocytes in other autoimmune diseases, we hypothesised that this specific subset of circulating innate immune cells would have pro-inflammatory characteristics in treatment-naïve patients presenting acutely with active ITP, and that this would be reversed following successful prednisolone GC therapy. Peripheral blood mononuclear cells (PBMCs) were isolated from newly diagnosed treatment-naïve ITP patients (n=7) and from healthy controls (HC; n=10). All patients donated blood again 2 weeks after starting standard treatment with oral prednisolone. The frequency of classical (CD14++CD16-), intermediate (CD14++CD16+), and non-classical (CD14+CD16++) monocyte subsets was then quantified for each sample using multiparameter flow cytometry. We found that there was a significant increase in the proportion of intermediate monocytes in treatment naïve ITP patients compared with HCs (12.7 vs 25.7%, respectively, p<0.0001), but this equalised following GC treatment (9.94% vs. 12.7% respectively, p=0.169). The proportion of intermediate monocytes from treatment-naïve ITP patients expressing the pro-inflammatory cell surface marker CD80 was also increased compared with HCs (0.43% vs. 0.20%, respectively p=0.013), and this decreased following GC-treatment (0.12%, p=0.002). Furthermore, expression of the anti-inflammatory scavenger receptors CD163 and CD206 was also increased (p=0.049) in intermediate monocytes taken from patients who had received 2 weeks of prednisolone. To interrogate whether these anti-inflammatory intermediate monocyte characteristics could be induced by GCs in vitro, monocytes from HC and ITP patients who had previously received systemic immunosuppressive therapy, were cultured with the synthetic GC dexamethasone for 24hrs and then phenotyped by flow cytometry. Both HC (n=10) and ITP (n=11) in vitro GC-treated intermediate monocytes demonstrated increased CD163 (p<0.0001) and CD206 (p<0.0001). Furthermore, the increase in CD163 and CD206 was similar between both HC and ITP donors (p=0.088, p=0.0775, respectively). These preliminary data show that newly diagnosed ITP patients present with an expanded population of CD14+CD16+ intermediate monocytes expressing pro-inflammatory cell surface markers. Hence, these innate immune cells may contribute to the pathogenesis of ITP by promoting T and B cell activation. Similarly, the immunosuppressive effect of prednisolone treatment may in part be mediated by a GC driven switch of intermediate monocytes to an anti-inflammatory state. If these results are replicated in independent patient cohorts, the characteristics of intermediate monocytes have potential translational utility as a biomarker of ITP disease activity and response to GC therapy.
|Title of host publication||BRITISH JOURNAL OF HAEMATOLOGY|
|Publication status||Published - 1 Mar 2019|