P140 Peptide in Lupus Figure 6. Proposed mechanisms underlying P140 peptide protective effect against disease in MRL/lpr mice. P140 physically associates with a unique receptor, the constitutive HSC70 chaperone protein, which is present on a majority (if not all) of immune cells. The P140-HSC70 complex (but not the putative complex encompassing the non-phosphorylated peptide 131–151) directly or indirectly activates cd T cells. Via a granzyme B- and caspase-dependent mechanism, apoptosis targeting activated CD4+ T blasts, CD8+ T cells, CD42CD8 2 B220+ T cells and B cells is induced (directly or via another cytotoxic effector) leading to a diminution of T-cell help to B cells, a diminution of antigen-presenting cell activity by B cells and a drop of antibody production by autoreactive B cells. In parallel, activated cd T cells secrete cytokines that modulate the ab T cell fate. This model does not exclude the possibility that in parallel, P140 also induces anergy, deletion, or deviation of autoimmune T cells, via antagonism or partial agonism of the ab T lymphocytes TCR [3]. In addition, P140 acts on non-activated CD4+ T cells by altering several intracellular pathways, leading, in particular, to dramatic effects on the NFkB and TNF pathways, and diminution of PD-1 expression, which is raised in MRL/lpr mice. doi:10.1371/journal.pone.0005273.g006 level in clinically normal skin and a decreased level at the periphery, which in some studies correlate with disease activity [32–34]. MRL/lpr mice lacking cd T cells develop more severe disease [11]. Restoring cd T cell functions might therefore constitute an important step [35]. Upon administration of P140 into MRL/lpr mice, activated T and B cells as well as DN T cells were found to be engaged in an apoptotic process. This observation is crucial in the P140 pathway since early mortality of MRL/lpr mice is associated to T cell lymphoaccumulation reminiscent of lpr-related lymphoproliferative disease. How cd cell- mediated P140-induced killing precisely occurs remains to be elucidated. Ex vivo, this Fas/FasL-independent process involves granzyme-B and caspases but apparently not perforin. Knowing that cd T cells express CD40, an important co-stimulation might also occur via CD40L(CD154), which is expressed in a sustained manner at the surface of lupus CD4+ T cells and B cells [36]. CD16(FccRIII), the low affinity Fc receptor for IgG expressed by cd T cells (and not by ab T cells), may also play an important role; it was shown, for example, that soluble CD16 administered to lupus mice after the onset of disease has a beneficial effect on their biological and clinical behavior [37]. Although the absolute number of cd T cells is low in normal and lupus conditions, this small population of regulatory cells exerts numerous central effects [8,23]. Thus, upon activation, they might influence dendritic cells, NK cells, ab T cells, and via either contact-dependent mechanisms or chemiokine/cytokine secretion, might contribute to tolerance restoration in P140-treated mice. Beside this mechanism, which affects activated lymphocytes, P140 also alters properties of non-activated CD4+ T cells. Thus, hyperexpression in MRL/lpr mice of PD-1(CD279) molecule, a member of the CD28 family, which is a hallmark of activated T cells [38], is reversed in P140-treated mice. After P140 treatment other genes were significantly up-regulated, such as genes coding for STAT6 that promotes Th2-cell differentiation and NFkB1/ p50, or down-regulated, such as genes coding for adhesion molecule ICAM-1, IL-15, IL-5 and CFS2 cytokines, transcrip- tional regulator FOXP2, CDK4 (blocking the formation of cyclin- D/CDK4 complexes in murine lupus was shown to inhibit antigen-induced and anti-CD3-mediated splenic T cell prolifera- tion as well as T-dependent B cell activation and proliferation in vitro [39]), the E3 ligase Itch, and TNFSF10(TRAIL) (a member of the TNF ligand superfamily, which exacerbates lupus [40]). PLoS ONE | www.plosone.org 8 April 2009 | Volume 4 | Issue 4 | e5273