By identifying the lipid LPC as an endogenous antigen, recognized by the invariant subset of human NKT cells, this study establishes a novel link between these immunoregulatory cells and an inflammatory lipid mediator.

CD1d-restricted NKT cells use structurally conserved TCRs and recognize both self and foreign glycolipids, but the TCR features that determine these Ag specificities remain unclear. We investigated the TCR structures and lipid Ag recognition properties of five novel Vα24-negative and 13 canonical Vα24-positive/Vβ11-positive human NKT cell clones generated using α-galactosylceramide (α-GalCer)-loaded CD1d tetramers. The Vα24-negative clones expressed Vβ11 paired with Vα10, Vα2, or Vα3. Strikingly, their Vα-chains had highly conserved rearrangements to Jα18, resulting in CDR3α loop sequences that are nearly identical to those of canonical TCRs. Vα24-positive and Vα24-negative clones responded similarly to α-GalCer and a closely related bacterial analog, suggesting that conservation of the CDR3α loop is sufficient for recognition of α-GalCer despite CDR1α and CDR2α sequence variation. Unlike Vα24-positive clones, the Vα24-negative clones responded poorly to a glucose-linked glycolipid (α-glucosylceramide), which correlated with their lack of a conserved CDR1α amino acid motif, suggesting that fine specificity for α-linked glycosphingolipids is influenced by Vα-encoded TCR regions. Vα24-negative clones showed no response to isoglobotrihexosylceramide, indicating that recognition of this mammalian lipid is not required for selection of Jα18-positive TCRs that can recognize α-GalCer. One α-GalCer-reactive, Vα24-positive clone differed from the others in responding specifically to mammalian phospholipids, demonstrating that semi-invariant NKT TCRs have a capacity for private Ag specificities that are likely conferred by individual TCR β-chain rearrangements. These results highlight the variation in Ag recognition among CD1d-restricted TCRs and suggest that TCR α-chain elements contribute to α-linked glycosphingolipid specificity, whereas TCR β-chains can confer heterogeneous additional reactivities.

Abetalipoproteinemia (ABL) is a rare Mendelian disorder of lipid metabolism due to genetic deficiency in microsomal triglyceride transfer protein (MTP). It is associated with defects in MTP-mediated lipid transfer onto apolipoprotein B (APOB) and impaired secretion of APOB-containing lipoproteins. Recently, MTP was shown to regulate the CD1 family of lipid antigen-presenting molecules, but little is known about immune function in ABL patients. Here, we have shown that ABL is characterized by immune defects affecting presentation of self and microbial lipid antigens by group 1 (CD1a, CD1b, CD1c) and group 2 (CD1d) CD1 molecules. In dendritic cells isolated from ABL patients, MTP deficiency was associated with increased proteasomal degradation of group 1 CD1 molecules. Although CD1d escaped degradation, it was unable to load antigens and exhibited functional defects similar to those affecting the group 1 CD1 molecules. The reduction in CD1 function resulted in impaired activation of CD1-restricted T and invariant natural killer T (iNKT) cells and reduced numbers and phenotypic alterations of iNKT cells consistent with central and peripheral CD1 defects in vivo. These data highlight MTP as a unique regulator of human metabolic and immune pathways and reveal that ABL is not only a disorder of lipid metabolism but also an immune disease involving CD1.

Breast cancer malignancy is promoted by the small GTPases RhoA and RhoC. SmgGDS is a guanine nucleotide exchange factor that activates RhoA and RhoC in vitro. We previously reported that two splice variants of SmgGDS, SmgGDS-607 and SmgGDS-558, have different characteristics in binding and transport of small GTPases. To define the role of SmgGDS in breast cancer, we tested the expression of SmgGDS in breast tumors, and the role of each splice variant in proliferation, tumor growth, Rho activation, and NF-κB transcriptional activity in breast cancer cells. We show upregulated SmgGDS protein expression in breast cancer samples compared to normal breast tissue. Additionally, Kaplan-Meier survival curves indicated that patients with high SmgGDS expression in their tumors had worse clinical outcomes. Knockdown of SmgGDS-558, but not SmgGDS-607, in breast cancer cells decreased proliferation, in vivo tumor growth, and RhoA activity. Futhermore, we found that SmgGDS promoted a Rho-dependent activation of the transcription factor NF-κB, which provides a potential mechanism to define how SmgGDS-mediated activation of RhoA promotes breast cancer. This study demonstrates that elevated SmgGDS expression in breast tumors correlates with poor survival, and that SmgGDS-558 plays a functional role in breast cancer malignancy. Taken together, these findings define SmgGDS-558 as a unique promoter of RhoA and NF-κB activity and a novel therapeutic target in breast cancer.

Monocytes can differentiate into macrophages or dendritic cells (DCs). The processes that promote their differentiation along one pathway rather than the other remain unknown. NKT cells are regulatory T cells that respond functionally to self and foreign antigens presented by CD1d molecules. Hence, in addition to contributing to antimicrobial responses, they may carry out autoreactively activated functions when there is no infectious challenge. However, the immunological consequences of NKT cell autoreactivity remain poorly understood. We show here that human NKT cells direct monocytes to differentiate into immature DCs. The ability to induce monocyte differentiation was CD1d-dependent and appeared specific to NKT cells. Addition of exogenous antigens or costimulation from IL-2 was not required but could enhance the effect. DC differentiation was a result of NKT cell secretion of GM-CSF and IL-13, cytokines that were produced by the NKT cells upon autoreactive activation by monocytes. NKT cells within PBMC samples produced GM-CSF and IL-13 upon exposure to autologous monocytes directly ex vivo, providing evidence that such NKT cell-autoreactive responses can occur in vivo. These results show that when NKT cells are activated by autologous monocytes, they are capable of providing factors that specifically direct monocyte differentiation into immature DCs. Thus, autoreactively activated NKT cells may contribute to the maintenance of the immature DC population, and microbial infection or inflammatory conditions that activate NKT cells further could stimulate them to promote an increased rate of DC differentiation.