The pentameric C-reactive protein (pCRP), an acute-phase protein, binds to lysophosphatidylcholine (LPC) displayed on the surface of dying cells and microorganisms to activate the complement system and to opsonize immune cells via Fcγ-receptors (FcγRs). Members of the FcγR family are characterized by the recognition of the Fc part of IgG antibodies. We utilized a mouse thymoma BW5147 reporter cell panel stably expressing chimeric human FcγR-CD3ζ-chain receptors to define the molecular requirements for FcγR crosslinking by C-reactive protein (CRP). Applying this approach, we show a robust activation of CD64/FcγRI and CD32a/FcγRIIa by immobilized CRP isoforms as well as triggering of inhibitory CD32b/FcγRIIb. Of note, activation of FcγRIIa was restricted to the 131R allelic variant but not observed with 131H. In contrast, FcγRIII isoforms CD16aF, CD16aV and CD16b were not activated by pCRP, although binding of CRP isoforms to FcγRIII was detectable. Activation of FcγRs by free pCRP in solution phase was considerably lower than with immobilized pCRP on hydrophilic plastic surfaces and readily abolished by IgG at serum level concentrations, whereas it was enhanced by the addition of streptococci. The types of FcγRs mainly responding to pCRP in solution phase (CD64/FcγRI and CD32aR/FcγRIIaR) clearly differed from FcγRs responding to soluble multimeric IgG complexes (i.e., CD16aV/FcγRIIIaV and CD32aH/FcγRIIaH). Compared to pCRP, monomeric CRP (mCRP) showed lower levels of activation in those selective FcγRs. FcγR activation was linked to recognition by conformation-dependent CRP antibodies. Unmasking of the mAb 9C9-defined neoepitope in pCRP* correlated with the triggering of FcγRs, indicating that pCRP* is the major FcγR-activating CRP conformation. The assay provides a novel, scalable approach to determine the molecular properties of CRP as a physiological ligand of FcγR-mediated bioactivities. Scope statement Fcγ receptors (FcγRs) are important immune regulators that come in different variants and combinations, making it difficult to predict which components will ultimately lead to immunological effector functions. Classical FcγRs are defined by their recognition of IgG-Fc, while other ligands, such as C-reactive protein (CRP), are often neglected. Circulating concentrations of CRP, an acute phase protein, are elevated during inflammatory responses. As a pattern recognition receptor, CRP binds to lysophosphatidylcholine expressed on the surface of dying cells and microbes in order to activate the complement system via C1q. We have established a reporter cell assay platform that goes beyond ligand binding and takes a deeper look at the activation outcome(s) by CRP compared with IgG-Fc. This is the first comprehensive study defining CRP-responsive vs non-responsive FcγRs and investigating the interaction of FcγRs with CRP isoforms (pCRP/pCRP*/mCRP). We distinguish binding from receptor triggering using reporter cells stably expressing a chimeric FcγR-CD3ζ chain, thereby defining the molecular requirements for FcγR cross-linking by CRP. The assay provides a novel, sensitive and scalable approach to the properties of CRP as a ligand inducing FcγR-mediated bioactivities.

Plaques are a hallmark feature of Alzheimer's disease (AD). We found that the loss of mucosal-associated invariant T (MAIT) cells and their antigen-presenting molecule MR1 caused a delay in plaque pathology development in AD mouse models. However, it remains unknown how this axis is impacting dystrophic neurites.
Brain tissue from 5XFAD mice and those that are MR1 deficient (MR1 KO), were analyzed for dystrophic neurites, amyloid plaques, and synapses via immunofluorescence, RNA sequencing, enzyme-linked immunosorbent assay, and western blot.
In 8-month-old 5XFAD/MR1 KO mice, there was reduced expression of lysosomal-associated membrane protein 1, ubiquitin, and n-terminal amyloid precursor protein in the hippocampus compared to 5XFAD mice (P < 0.05). 5XFAD/MR1 KO mice also had less insoluble amyloid beta 40 (P < 0.001) and higher levels of postsynaptic density protein 95 (P < 0.01) in the hippocampus.
Our data contribute additional mechanistic insight into the detrimental role of the MR1/MAIT cell axis in AD pathology development.
5XFAD mice lacking the innate immune MR1/MAIT (mucosal-associated invariant T) cell axis (5XFAD/MR1 KO) have reduced numbers of dystrophic neurite markers in the hippocampus at 8 months of age. Hippocampal tissue transcriptional analyses showed reduced expression of genes encoding classical dystrophic neurite markers in 5XFAD/MR1 KO mice. 5XFAD/MR1 KO mice had less insoluble amyloid beta 40 and increased levels of the post-synaptic marker, postsynaptic density protein 95, in the hippocampus than did MR1+ 5XFAD mice.
© 2025 The Author(s). Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.

The adaptive T cell response is accompanied by continuous rewiring of the T cell's electric and metabolic state. Ion channels and nutrient transporters integrate bioelectric and biochemical signals from the environment, setting cellular electric and metabolic states. Divergent electric and metabolic states contribute to T cell immunity or tolerance. Here, we report in mice that neuritin (Nrn1) contributes to tolerance development by modulating regulatory and effector T cell function. Nrn1 expression in regulatory T cells promotes its expansion and suppression function, while expression in the T effector cell dampens its inflammatory response. Nrn1 deficiency in mice causes dysregulation of ion channel and nutrient transporter expression in Treg and effector T cells, resulting in divergent metabolic outcomes and impacting autoimmune disease progression and recovery. These findings identify a novel immune function of the neurotrophic factor Nrn1 in regulating the T cell metabolic state in a cell context-dependent manner and modulating the outcome of an immune response.
© 2024, Yu et al.

The adaptive T cell response is accompanied by continuous rewiring of the T cell’s electric and metabolic state. Ion channels and nutrient transporters integrate bioelectric and biochemical signals from the environment, setting cellular electric and metabolic states. Divergent electric and metabolic states contribute to T cell immunity or tolerance. Here, we report that neuritin (Nrn1) contributes to tolerance development by modulating regulatory and effector T cell function. Nrn1 expression in regulatory T cells promotes its expansion and suppression function, while expression in the T effector cell dampens its inflammatory response. Nrn1 deficiency causes dysregulation of ion channel and nutrient transporter expression in Treg and effector T cells, resulting in divergent metabolic outcomes and impacting autoimmune disease progression and recovery. These findings identify a novel immune function of the neurotrophic factor Nrn1 in regulating the T cell metabolic state in a cell context-dependent manner and modulating the outcome of an immune response.

Introduction: Among skin cancers, melanoma has a high mortality rate. Recent advances in immunotherapy, particularly through immune checkpoint modulation, have improved the clinical treatment of melanoma. Maltol has various bioactivities, including anti-oxidant and anti-inflammatory properties, but the anti-melanoma property of maltol remains underexplored. The aim of this work is to explore the anti-melanoma potential of maltol through regulating immune checkpoints. Methods: The immune checkpoint PD-L1 was analyzed using qPCR, immunoblots, and immunofluorescence. Melanoma sensitivity towards T cells was investigated via cytotoxicity, cell viability, and IL-2 assays employing CTLL-2 cells. Results: Maltol was found to reduce melanin contents, tyrosinase activity, and expression levels of tyrosinase and tyrosinase-related protein 1. Additionally, maltol suppressed the proliferative capacity of B16F10 and induced cell cycle arrest. Maltol increased apoptotic rates by elevating cleaved caspase-3 and PARP. The co-treatment with maltol and cisplatin revealed a synergistic effect on inhibiting growth and promoting apoptosis. Maltol suppressed IFN-γ-induced PD-L1 and cisplatin-upregulated PD-L1 by attenuating STAT1 phosphorylation, thereby enhancing cisplatin's cytotoxicity against B16F10. Maltol augmented sensitivity to CTLL-2 cell-regulated melanoma destruction, leading to an increase in IL-2 production. Discussion: These findings demonstrate that maltol restricts melanoma growth through the downregulation of PD-L1 and elicits T cell-mediated anti-cancer responses, overcoming PD-L1-mediated immunotherapy resistance of cisplatin. Therefore, maltol can be considered as an effective therapeutic agent against melanoma.
Copyright © 2023 Han, Park, Ko and Moon.