Selective induction of autocytotoxic activity through the CD3 molecule

Identification and characterization of a transmembrane isoform of CD160 (CD160-TM), a unique activating receptor selectively expressed upon human NK cell activation

CD160 has been initially identified as a GPI-anchored MHC-class I activating receptor mainly expressed on peripheral blood NK cells. Herein, we report the identification of three additional CD160-related mRNAs generated through alternative splicings of the CD160 gene, among which one encoded a putative CD160 transmembrane isoform (CD160-TM). We first establish that CD160-TM surface expression is highly restricted to NK cells and is activation-dependent. Additionally, we provide evidence that CD160-TM represents a novel activating receptor, as assessed by the increased CD107a NK cell surface mobilization observed upon its engagement. Finally, we demonstrate that the CD160-TM cytoplasmic tail is by itself sufficient to mediate the recruitment of Erk1/2 signaling pathway, and that the initiation of this activation process is dependent on the Src-family kinase p56(lck). The identification of CD160-TM therefore provides new possibilities regarding the role of CD160 isoforms in the regulation of NK cell functions.

The Role of Activation-Induced Cell Death in the Differentiation of T-Helper-Cell Subsets

Activation-induced cell death (AICD) has been demonstrated in T-cell hybridomas, immature thymocytes, and activated mature T cells. However, the molecular mechanisms of AICD and its physiological role in T-helper-cell differentiation remain uncertain. Recently, we have shown that Th1 and Th2 cells have distinct mechanisms of AICD. Our findings suggest that signaling from cytokines initiates the differentiation program, but that the selective action of death effectors determines the fate of differentiating T-helper cells, and thus, the ultimate balance between T-helper subpopulations. Among T cells, activation- induced expression of the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is observed exclusively in Th2 clones and primary T-helper cells differentiated under Th2 conditions, while the expression of CD95L (Fas ligand) occurs mainly in Th1 cells. Furthermore, Th1 cells are more susceptible than Th2 cells to apoptosis induced through either TRAIL or CD95L, and radiolabeled Th1 cells can be induced into apoptosis via fratricide by both Th1 and Th2 cells, while Th2 cells are spared. The pan-caspase inhibitor, z-VAD, prevents AICD in Th1 cells, but not Th2 cells, indicating different mechanisms of AICD in each T-helper subtype. Antibody blockade of TRAIL and CD95L significantly boosts interferon-gamma (IFN-gamma) production in vitro. Also, young mice with mutant CD95 (MRL/MpJ-lpr/lpr) have a stronger Th1 response to ovalbumin immunization than do controls. We conclude that apoptosis mediated by CD95L and TRAIL is critical in the selective removal of differentiating T helper cells.

G10.3 monoclonal antibody identifies novel functional cell surface structures expressed by normal B lymphocytes and various malignant cell lines

G10.3, a unique monoclonal antibody (mAb), was produced to better characterize lymphocyte subsets. In the present study, we show that this mAb identifies 118, 83 and 51 kDa cell surface sialylated glycoproteins on the immunizing cell line YTindi. The reactivity of G10.3 mAb is restricted in normal cells to B lymphocytes, whereas within tumoral cell lines various lymphoid and non-lymphoid cells were found positive. Interestingly, functional studies revealed that triggering G10.3 mAb reactive molecules with soluble antibody led to an inhibition of growth and to an induction of programmed cell death in tumor cell lines expressing high levels of reactive molecules.

Soluble CD14 acts as a negative regulator of human T cell activation and function

T cell activation is controlled by the coordination of stimulatory and negative regulatory signals which are not completely defined. In this study we tested for a possible direct effect of CD14 on the regulation of T cell activation and function. We show that soluble CD14 (sCD14) induces inhibition of antigen-mediated peripheral blood mononuclear cells (PBMC) proliferation and anti-CD3-mediated proliferation of CD4+CD8+, CD4+CD8+ and CD4+CD8+ Tcell clones. This effect is not due to cell death, but results from a marked inhibition of IL-2 production. Proliferation of T cell clones due to exogenous IL-2 is not affected by sCD14. We also found that sCD14 inhibits production of another Th1-like cytokine, IFN-gamma and a Th2-like cytokine, IL-4. Importantly, sCD14 induces a progressive accumulation of the inhibitory protein IkappaB-alpha. We show that sCD14 binds to activated T cells. Following cell activation, biotinylated sCD14 stains CD3+ PBMC, as well as human T cell clones with varying intensity. The binding is saturable, can be inhibited by excess of unlabeled sCD14 and, following binding, sCD14 is internalized. Collectively, these findings reveal a previously unrecognized function of sCD14, namely its capacity to negatively regulate T lymphocyte activation and function by interacting directly with activated T cells.

Identification of a novel functional 85-kD glycoprotein restricted to long-term dividing human lymphocytic lines

Lymphocyte activation induces or increases the expression of several surface structures, some of which are directly involved in cell growth such as receptors for IL2 or transferrin. To identify new structures characteristic of activated lymphocytes, we developed a series of mAbs against functionally defined human T-cell clones or the NK-mediating cell line YT2C2. In this study, we report the isolation of an mAb termed AY19 recognizing, at the cell surface, an 85-kD glycoprotein whose expression is restricted to T-lymphocyte clones, leukemic T-cell lines, and T-ALL peripheral blood cells. Biochemical studies, as well as phenotypic analysis, revealed that this structure is different from all previously identified molecules on the cell surface of lymphocytes. Furthermore, functional studies showed that triggering of this 85-kD structure on cloned T-lymphocytes through the AY19 epitope led to an inhibition of CD3-induced proliferation. These findings suggest that the AY19 mAb defines a T-cell antigen expressed mainly on long-term dividing lymphocytes and, therefore, its putative ligand might play a role in the regulation of T-lymphocyte growth induced by CD3-TcR stimulation.

The CD39 molecule defines distinct cytotoxic subsets within alloactivated human CD8-positive cells

Lymphocyte activation induces or increases the expression of several surface structures, none of which is characteristic of an activated cell subset. In particular, structures such as CD45RO, CD25, CD26, CD49b, CD54, CD71 are expressed by the vast majority of lymphocytes at various times following in vitro activation. CD39 molecules were originally identified on activated B lymphocytes and have recently been described on activated T cell clones. In the present report, we have characterized phenotypically and functionally defined cell subsets generated during an in vitro allostimulation. Results indicated that the percentage of CD39+ cells reached a maximum at day 6 and remained stable thereafter. We demonstrate that CD39 expression allows the identification within the allosensitized CD8+ cytotoxic cells of distinct subsets of cells mediating allo cytotoxic T lymphocyte or natural killer (NK)-like reactivity. More precisely, CD8+CD39+ alloactivated cells mainly mediate specific killer activity, whereas CD8+CD39- alloactivated cells predominantly exhibit NK-like reactivity. Further, we show a high functional correlation associated with the lack of CD39 expression on NK-like alloactivated CD8+ cells, while there is no association with CD56 or CD57 NK-associated structures.