- Most antigenic peptides that bind stably to a major histocompatibility complex (MHC) I molecule for display to the immune system are approximately the same length, thanks in part to the expert trimming done by endoplasmic reticulum aminopeptidases (ERAPs), the final peptidases in the antigen-presentation pathway. An open question is whether ERAPs edit peptides to this optimal length while they are bound to MHC I molecules (using the latter as a pattern of sorts) or by free hand. Mavridis et al. present multiple lines of evidence that this trimming cannot readily occur on MHC I molecules, but rather only in solution, suggesting that ERAPs work alone to tailor the perfect fit for the immunopeptidome.
- The PD-1 ligands PD-L1 and PD-L2 are commonly expressed on the surface of cells, where they regulate immune system activation. However, the specific role played by each ligand has been unclear. Using site-directed mutagenesis, surface plasmon resonance, and crystallography, Philips et al. explore the distinct features of PD-L2 and identify a specific evolutionary event linked to its appearance. This work provides a deeper understanding of how the immune system adapted to mammalian placental gestation and could be an important consideration in the development of new immune checkpoint therapies.
- Chronic recurrent multifocal osteomyelitis (CRMO) is an autoinflammatory bone disease mediated by the inflammatory cytokine, IL-1β. Although IL-1β is known as the key driver of bone lesions in CRMO, the signaling events leading to pathogenic levels of the cytokine are not fully understood. Using a genetic mouse model of CRMO, Dasari et al. find a role for the nonreceptor spleen tyrosine kinase (SYK) in upstream signaling leading to IL-1β up-regulation. Their findings suggest that SYK may constitute a new therapeutic target for CRMO.
- T-cell receptors (TCRs) recognize pathogens to ignite immune responses, making them attractive scaffolds for development as immunotherapeutics. However, manipulation of TCRs has been impeded by difficulties in their engineering and expression. Wagner and colleagues now establish new platforms to generate high-affinity TCR variants that potently activate T cells, and they also create soluble TCR fusion proteins that specifically recognize cognate peptides. This work provides specific tools to combat cytomegalovirus (CMV) infection and helps illuminate a general path to actuation of engineered TCR-based therapeutics.
- T-cell receptors (TCR) have considerable potential as therapeutics and antibody-like reagents to monitor disease progression and vaccine efficacy. Whereas antibodies recognize only secreted and surface-bound proteins, TCRs recognize otherwise inaccessible disease-associated intracellular proteins when they are presented as processed peptides bound to major histocompatibility complexes (pMHC). TCRs have been primarily explored for cancer therapy applications but could also target infectious diseases such as cytomegalovirus (CMV).
- Poxviruses have evolved efficient proteins that bind mammalian cytokines and chemokines to suppress host immunity. Here Pontejo et al. examine in detail how one such poxviral protein, CrmD, that has activity against both mammalian tumor necrosis factor and chemokines, interacts with its host targets. They apply their findings to refine a human anti-cytokine therapeutic and increase its specificity, providing an elegant example of the benefits of mining viral proteins for therapeutically useful information.
- Inflammasomes enable cells to respond to pathogens or biological damage, but the specific signals being used to convey these messages are not always clear. A new paper identifies two potential microbiota-derived metabolites, the bile acid analogues BAA485 and BAA473, as the first small molecules to activate the pyrin inflammasome. These results suggest that microbiota may be able to modulate this inflammatory process which, in turn, may contribute to the maintenance of intestinal homeostasis.