The effects of Pseudomonas aeruginosa quorum sensing signalling molecules on human T cell function

Quorum sensing signalling molecules (QSSMs) are important to Pseudomonas aeruginosa virulence and biofilm development which aid establishment and persistence of these bacteria in the host. Recent progress in quorum sensing (QS) research has demonstrated that the two QSSMs, 3-oxo-C12-HSL and PQS interact with eukaryotic cells and modulate immune responses. Early research has indicated these two QSSMs are immunosuppressive, and because T cells play an important role in defending the host against the attack of P. aeruginosa (Stevenson et al., 1995), this warrants investigations into the interactions between QSSMs and T cells. Previous studies have shown 3-oxo-C12-HSL and PQS can exert differential immune-modulatory effects on mammalian immune responses, however, no studies have confirmed these activities using pure human T cells. The purpose of my PhD was to investigate for the first time, the effects of these two QSSMs on pure human T cells in a staged manner, beginning with mouse splenocytes, human peripheral blood mononuclear cells (hPBMCs) and finally pure T cells, then if successful, paving the way for gene array technology. This present work confirms inhibitory effects by QSSMs on mouse splenocytes stimulated to proliferate using the lectin concanavalin (ConA) or anti-CD3 antibody, and hPBMCs stimulated to proliferate using anti-CD3 and anti-CD28 antibody. In order to further understand interactions between QSSMs and the immune system, the effects of 3-oxo-C12-HSL and PQS on pure human T cell proliferation and cytokine production following stimulation of T cells with monoclonal antibodies directed against CD3 and CD28 were compared, using CsA as the positive control. All three compounds inhibited pure T cell proliferation. CsA and PQS were the more potent anti-proliferative compounds with IC50 values of 3.2±0.31 µM and 3.8±0.15 µM respectively compared to 19±1.62 µM for 3-oxo-C12-HSL, indicating the QSSMs ability to suppress T cell activity and therefore ad