A critical role for suppressor of cytokine signalling 3 in promoting M1 macrophage activation and function in vitro and in vivo.

Macrophages respond to their microenvironment and develop polarized functions critical for orchestrating appropriate inflammatory responses. Classical (M1) activation eliminates pathogens while alternative (M2) activation promotes regulation and repair. M1 macrophage activation is strongly associated with suppressor of cytokine signalling 3 (SOCS3) expression in vitro, but the functional consequences of this are unclear and the role of SOCS3 in M1-macrophage polarization in vivo remains controversial. To address these questions, we defined the characteristics and function of SOCS3-expressing macrophages in vivo and identified potential mechanisms of SOCS3 action. Macrophages infiltrating inflamed glomeruli in a model of acute nephritis show significant up-regulation of SOCS3 that co-localizes with the M1-activation marker, inducible nitric oxide synthase. Numbers of SOCS3(hi) -expressing, but not SOCS1(hi) -expressing, macrophages correlate strongly with the severity of renal injury, supporting their inflammatory role in vivo. Adoptive transfer of SOCS3-short interfering RNA-silenced macrophages into a peritonitis model demonstrated the importance of SOCS3 in driving production of pro-inflammatory IL-6 and nitric oxide, while curtailing expression of anti-inflammatory IL-10 and SOCS1. SOCS3-induced pro-inflammatory effects were due, at least in part, to its role in controlling activation and nuclear accumulation of nuclear factor-κB and activity of phosphatidylinositol 3-kinase. We show for the first time that SOCS3 also directs the functions of human monocyte-derived macrophages, including efficient M1-induced cytokine production (IL-1ß, IL-6, IL-23, IL-12), attenuated signal transducer and activator of transcription 3 activity and ability of antigen-loaded macrophages to drive T-cell responses. Hence, M1-associated SOCS3 was a positive regulator of pro-inflammatory responses in our rodent models and up-regulated SOCS3 is essential for effective M1-macrophage activation and function in human macrophages.

Physiological strength electric fields modulate human T cell activation and polarisation.

The factors and signals driving T cell activation and polarisation during immune responses have been studied mainly at the level of cells and chemical mediators. Here we describe a physical driver of these processes in the form of physiological-strength electric fields (EFs). EFs are generated at sites where epithelium is disrupted (e.g. wounded skin/bronchial epithelia) and where T cells frequently are present. Using live-cell imaging, we show human primary T cells migrate directionally to the cathode in low strength (50/150 mV/mm) EFs. Strikingly, we show for the first time that EFs significantly downregulate T cell activation following stimulation with antigen-activated APCs or anti-CD3/CD28 antibodies, as demonstrated by decreased IL-2 secretion and proliferation. These EF-induced functional changes were accompanied by a significant dampening of CD4+ T cell polarisation. Expression of critical markers of the Th17 lineage, RORγt and IL-17, and the Th17 polarisation mediator phospho-STAT3 were reduced significantly, while STAT1, ERK and c-Jun phosphorylation were comparatively unaffected suggesting STAT3 modulation by EFs as one mechanism driving effects. Overall, we identify electrical signals as important contributors to the co-ordination and regulation of human T cell functions, paving the way for a new research area into effects of naturally occurring and clinically-applied EFs in conditions where control of T cell activity is paramount.

The activation status of human macrophages presenting antigen determines the efficiency of Th17 responses.

Macrophages are antigen presenting cells that can adopt different activation states as directed by microenvironmental stimuli. It is well-recognised how CD4(+) T helper (Th) signals drive macrophage activation, but the ability of differentially activated human macrophages to stimulate the major types of CD4(+) T helper (Th) response by presenting antigen have not been well defined. Previous studies have focussed on murine cells, undifferentiated human monocytes, or macrophage products, and have been limited to non-physiological mitogenic Th responses. The aim was therefore to compare the Th cell polarising abilities of different human macrophage subsets when presenting specific antigen. We demonstrate for the first time that the way macrophages are activated, while naturally presenting antigen, has profound effects on downstream adaptive immune responses. In autologous co-cultures, LPS-activation was the most potent stimulus for antigen-loaded macrophages to drive Th17 polarisation from both unfractionated CD4(+) T-cells and the CD45RO(+) memory population, while IFNγ/LPS activated macrophages preferentially induced a Th1 phenotype. By contrast, IL-4-activated macrophages were ineffective in inducing responses by either Th subset. Although antigen-loaded dendritic cells were superior to macrophages in driving Th1 responses, the Th17 polarising capacity of the two antigen-presenting cell types was equivalent, and was strongly dependent on IL-1ß secretion. Taken together, these results clearly demonstrate for the first time how differentially activated human macrophages present antigen to bias specific, rather than mitogen-driven, Th responses and lead us to propose that they impact adaptive immunity in vivo, particularly in determining Th17 polarisation within inflamed tissues.