Trafficking through the Endocytic Pathway Presentation to NKT Cells by Altering CD1d Bcl-xL Regulates CD1d-Mediated Antigen

NKT cells are a unique subset of T cells that recognize glycolipid Ags presented in the context of CD1d molecules. NKT cells mount strong antitumor responses and are a major focus in developing effective cancer immunotherapy. It is known that CD1d molecules are constantly internalized from the cell surface, recycled through the endocytic compartments, and re-expressed on the cell surface. However, little is known about the regulation of CD1d-mediated Ag processing and presentation in B cell lymphoma. Prosurvival factors of the Bcl-2 family, such as Bcl-xL, are often upregulated in B cell lymphomas and are intimately linked to sphingolipid metabolism, as well as the endocytic compartments. We hypothesized that Bcl-xL can regulate CD1d-mediated Ag presentation to NKT cells. We found that overexpression or induction of Bcl-xL led to increased Ag presentation to NKT cells. Conversely, the inhibition or knockdown of Bcl-xL led to decreased NKT cell activation. Furthermore, knockdown of Bcl-xL resulted in the loss of CD1d trafficking to lysosome-associated membrane protein 1 + compartments. Rab7, a late endosomal protein, was upregulated and CD1d molecules accumulated in the Rab7 + late endosomal compartment. These results demonstrate that Bcl-xL regulates CD1d-mediated Ag processing and presentation to NKT cells by altering the late endosomal compartment and changing the intracellular localization of CD1d. N atural killer T cells are a unique subset of T cells that recognize lipid Ags presented by CD1d, an MHC class I–like molecule (1–3). Once activated, NKT cells can mediate direct cytotoxicity and also rapidly produce large amounts of cytokines such as IFN-g and IL-4. One of the most striking and well-established functions of NKT cells is their antitumor effect, mediated directly by cytotoxicity, as well as indirectly by cytokine production, leading to the recruitment and activation of other cell types (4–6). However, the precise mechanisms that underlie the recognition of tumors by NKT cells, in the absence of an exog-enous activating Ag like the prototypical a-galactosylceramide (a-GalCer), remain poorly understood. In contrast to the MHC restriction of classical T cells, NKT cells are CD1d restricted (7, 8). Mice possess CD1d1 and CD1d2 genes; however, Ag presentation to NKT cells is dependent upon CD1d1 molecules (referred to as CD1d). The CD1d molecule is structurally similar to MHC class I with a three-domain a-chain that associates with b 2-microglobulin, but unlike the classical MHC class I molecule, CD1d has a hydrophobic Ag binding groove (9, 10). Also, in contrast with …