NK cell-mediated lysis of autologous antigen-presenting cells is triggered by the engagement of the phosphatidylinositol 3-kinase upon ligation of the natural cytotoxicity receptors NKp30 and NKp46.

Interleukin-2 (IL-2)-activated polyclonal or clonal NK cells lysed autologous antigen presenting cells (APC) through the engagement of the natural cytotoxicity receptors (NCR) NKp30 and NKp46. NK cell-mediated cytolysis of APC correlated with the surface density of these NCR. Indeed, NK cell clones bearing low amounts of NKp30 and NKp46 did not lyse autologous APC, whereas NK cell clones with bright expression of these NCR efficiently killed autologous APC. Upon masking of NKp30 or NKp46 by specific monoclonal antibodies a strong reduction (by 50%) of APC lysis could be detected and the complete inhibition was achieved by the simultaneous masking of these NCR. Interestingly, NK cell-mediated APC lysis was impaired by the phosphatidylinositol 3-kinase (PI-3 K) inhibitors LY294002 or wortmannin. Similarly, these drugs strongly reduced NK cell activation triggered by NKp30 or NKp46 in a re-directed killing assay as well as the activation of Akt/PKB, substrate of PI-3 K, induced by the engagement of these receptors. Altogether, these findings strongly suggest that NCR are responsible for the killing of autologous APC through the activation of PI-3 K.

Dendritic cells efficiently cross-prime HLA class I-restricted cytolytic T lymphocytes when pulsed with both apoptotic and necrotic cells but not with soluble cell-derived lysates.

Dendritic cells (DC) have been shown to efficiently present antigen to CD8(+) cytolytic T cells (CTL) when pulsed with apoptotic cells as a source of cell-derived antigen. Such cross-priming could not be detected by the use of necrotic cells, while conflicting results have been reported for cell-derived soluble lysates. In this study, we reinvestigated this issue by using autologous Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL) as a source of antigen to pulse monocyte-derived DC. Both autologous and HLA-mismatched allogeneic LCL have been used either in the form of apoptotic or of necrotic cells or of soluble cell lysates. At day 7, DC were co-cultured with the autologous CD8(+) lymphocyte fraction for an additional 9 days, in the presence of exogenous IL-2 (added after 48 h). At the end of the culture period, CD8(+) CTL efficiently lysed autologous LCL only when they had been co-cultured with DC pulsed with necrotic or apoptotic cells. That an efficient cross-priming of autologous CD8(+) cells could be induced by DC pulsed with apoptotic or necrotic LCL but not with cell lysates was further demonstrated in assays of IFN-gamma production in response to short-term re-stimulation of CD8(+) cells with LCL. In addition, LCL-specific CD8(+) cells could specifically lyse autologous DC that had been pulsed with LCL-derived antigens, further suggesting that DC presented exogenous antigens on HLA class I molecules.

Engagement of CD33 surface molecules prevents the generation of dendritic cells from both monocytes and CD34+ myeloid precursors.

Although CD33 represents an important marker of myeloid cell differentiation, its function remains poorly defined. In view of its homology with p75/AIRM1, a recently identified surface molecule which exerts a potent inhibition on NK cell function, we re-evaluated the effect of CD33 engagement in defined myeloid cell functions. Addition of anti-CD33 mAb to cultures of CD14+ monocytes supplemented with granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-4 and TNF-alpha, prevented the generation of dendritic cells. In these cultured cells, engagement of CD33 resulted in an increased surface binding of annexin-V, followed by cell death. Mature dendritic cells were resistant to the CD33-mediated effect. Also in CD34+ precursors, cultured in the presence of flt3-ligand, c-Kit-ligand, GM-CSF, IL-4 and TNF-alpha, addition of anti-CD33 mAb prevented the recovery of mature dendritic cells. These data suggest a regulatory role of CD33 in the myeloid cell maturation and may offer a tool to interfere with the monocyte/macrophage cell function as well as with the development of dendritic cells.