Just a part of CD8+LAP+cells exhibit CD25 or Foxp3, even though the expression degrees of Foxp3 for these cells are greater than their LAPcounterparts. == Launch == The disease fighting capability has evolved many systems, including deletion, anergy, and legislation, to regulate the differentiation and enlargement of activated T cells. Treg are specific subpopulations of T cells that modulate the disease fighting capability to avert undesired immune system responses and therefore donate to maintenance of immunological self-tolerance and immune system homeostasis [13]. Whereas Compact disc4+Treg subsets have already been extensively studied, less is known about CD8+Treg, their subsets, and modes of action. Several lines of evidence suggest that CD8+T cells are important in regulation of EAE [46] even though there are reports that EAE can be induced by CD8+T cells [7,8]. Depletion of CD8+T cells from mice that have recovered from EAE renders them susceptible to reinduction of disease [5] and CD8/mice develop more chronic EAE manifested by a higher incidence of relapse than WT animals [6]. Distinct subpopulations of CD8+Treg, including CD8+CD28and CD8+CD122+Treg, which can regulate EAE, have been identified [9,10]. Moreover, experiments in 2 microglobulin/mice, in which CD8+T cells do not develop due to MHC I deficiency, suggest a regulatory role for CD8+T cells in EAE [11]. CD8+T cells isolated from EAE-recovered mice specifically inhibit MBP-activated CD4+T-cell clonesin vitroand their depletion was followed by recurrence of EAE. The suppressive function of these CD8+T cells is restricted by MHC I-like Qa-1 molecule (murine homologue of the human HLA-E) and adoptive transfer of these cells prevented disease in MBP-immunized mice [1214]. The failure of resistance to EAE of Qa-1-deficient mice is associated with the escape of Qa-1-deficient CD4+cells from CD8+T-cell suppression [15]. Taken together, these VR23 results provide evidence that CD8+T cells are important in both inducing resistance to EAE and abrogating recurrent relapsing episodes of pathogenic autoimmunityin vivo. Various modes of action have been reported for CD8+Treg, including the production of soluble factors, such as immuno-suppressive cytokines IL-10 or TGF- [1619], direct killing of target cells [12,1921], targeting APC and rendering them tolerogenic [19,22], or by noncytolytic pathways that have not been clearly defined. We and others have previously shown that CD4+T cells expressing latency-associated peptide (LAP) actively suppress autoimmune diseases in experimental models of colitis and EAE and function in a TGF–dependent manner [2325]. LAP is the N-terminal propeptide of TGF- precursor peptide that remains noncovalently associated with TGF- after cleavage from TGF- precursor and forms the inactive latent TGF- complex; it therefore contributes to the prevention of uncontrolled activation of the cognate TGF- receptors [26,27]. It is not known whether CD8+LAP+cells existin vivoin animal models and whether they function as regulatory cells in autoimmune diseases such as EAE. In the present study, we identify a novel subset of CD8+Treg that express LAP on their surface and suppress EAE in a TGF- and IFN–dependent fashion. == Results == == CD8+LAP+cells are regulatoryin vitro == To investigate the role of CD8+LAP+T cells, we first determined their presence and frequency in nave mice. In nave mice CD8+cells constitute 1012% of splenocytes, of which ~3.3% express LAP (Fig. 1A). CD8+LAP+cells were also present in thymus and lymph nodes but at lower frequency (not shown). To further characterize the function of CD8+LAP+cells, we examined whether CD8+LAP+cells exhibit regulatory functionin vitro. As Has2 shown inFig. 1B, CD8+LAP+cells significantly suppressed the proliferation of responder cells (CD4+CD25LAPcells), and this was evident for CD8+LAP+cells sorted from both nave SJL VR23 and B6 mice, although the cells from B6 mice appeared to have greater suppressive activity (Fig. 1B). No suppressive effect was observed for CD8+LAPcells (Fig. 1B). The suppression mediated by CD8+LAP+cells did not depend VR23 on cell-to-cell contact because CD8+LAP+cells suppressed the proliferation of responder cells equally as well across a transwell membrane (not shown), and there was no evidence of cell death in the responder cell population as measured by CFSE labeling (not shown). We then measured the effect of CD8+LAP+T cells on VR23 IFN- production by responder cells. As shown inFig. 1C, CD8+LAP+cells inhibited IFN- production by responder cells. These data indicate that CD8+LAP+cells possess regulatory activityin.