LTBR Human

What is the molecular structure of human LTBR and how does it compare to murine models?

Human LTBR is a 435 amino acid protein including a 30 aa signal peptide, a 197 aa extracellular domain containing four cysteine-rich motifs characteristic of TNF receptor superfamily, a 21 aa transmembrane domain, and a 187 aa cytoplasmic domain . Within the extracellular domain, human LTBR shares 67-74% amino acid sequence identity with mouse, rat, canine, porcine, equine, and bovine LTBR . When designing cross-species experiments, researchers should consider these structural similarities and differences, particularly when developing targeting antibodies or recombinant proteins.

Which cell types express LTBR and what methodologies best detect this expression?

LTBR is constitutively expressed on stromal cells and myeloid lineage cells but not on T or B lymphocytes . For detection, researchers should employ a multi-modal approach:

• RNA sequencing for transcriptomic profiling

• Flow cytometry for quantitative assessment in specific cell populations

• Immunohistochemistry for tissue localization

• Immunofluorescence for subcellular localization, which has revealed LTBR is primarily located in the Golgi apparatus in cancer cells

What are the primary signaling mechanisms of LTBR and how do they vary by cell type?

LTBR is activated by two distinct ligands:

• Lymphotoxin heterotrimer LTα1β2 expressed on activated T, B, and NK cells

• LIGHT homotrimer mostly expressed on activated T cells

The downstream effects vary by cell type. In macrophages, LTBR activation by T cell-derived LTα1β2 acts as a counterregulatory signal against exacerbating inflammatory reactions , suggesting an immunosuppressive role. In hepatocytes, LTBR signaling influences lipid metabolism and is upregulated during regeneration, hepatitis, and hepatocellular carcinoma .

How does LTBR expression vary across different cancer types and what does this suggest about its function?

LTBR shows significant differential expression across cancer types. Analysis of copy number and gene expression data revealed significant differences in 18 tumors . LTBR exhibits highest expression in:

• Lung squamous cell carcinoma (LUSC)

• Bladder cancer (BLCA)

• Esophageal carcinoma (ESCA)

And lowest expression in:

• Lower-grade glioma (LGG)

• Diffuse large B-cell lymphoma (DLBC)

• Glioblastoma multiforme (GBM)

TCGA database analysis shows significant upregulation of LTBR in 16 different cancer types compared to normal tissues , suggesting its potential role as an oncogene in these specific cancers.

What methodologies are most effective for analyzing LTBR's prognostic value in cancer?

Researchers typically employ multiple complementary approaches:

These are frequently used to establish predictive profiles of tumor-associated biomarkers. When conducting these analyses, researchers should consider clinical stages, immune subtypes, and molecular subtypes as potential confounding variables.

How does LTBR expression in tumor-associated macrophages (TAMs) differ from other immune cells?

Single-cell RNA sequencing data from human lung adenocarcinoma (LUAD) reveals that the highest mRNA level of LTBR is observed in TAMs rather than other tumor-infiltrated immune cells or even macrophages of normal lung tissues . This finding is further validated by fluorescence-activated cell sorter (FACS) assay in murine lung cancer models . Researchers investigating LTBR in the tumor microenvironment should specifically isolate TAM populations using markers such as CD11b+F4/80+ for accurate assessment.

What experimental models best represent LTBR function in human hematological malignancies?

For studying LTBR in acute myeloid leukemia (AML), the retrovirally-induced MLL-AF9 syngeneic AML mouse model has proven effective . Key methodological approaches include:

• Generating Light- and Ltbr-deficient MLL-AF9 transduced leukemia stem cells (LSCs)

• Intravenous injection into non-irradiated BL/6 recipient mice

• Evaluation of AML development by analyzing MLL-AF9-GFP-positive leukemic cells in blood, spleen, and bone marrow

• Phenotypic characterization of bone marrow LSCs by flow cytometry

• Functional assessment through:

  • Colony forming unit (CFU) assays in vitro

  • Secondary transplantations of LSCs including limited dilution assays (LDA) in vivo

What techniques are recommended for targeting LTBR signaling in research applications?

Several approaches have been validated:

• Genetic manipulation:

  • siRNA treatment for transient knockdown

  • CRISPR-Cas9 for generating knockout cell lines and animal models

• Pharmacological inhibition:

  • Novel LIGHT-targeting monoclonal antibodies that block LTBR signaling

  • Recombinant LTBR-Fc chimera proteins that act as decoys for LIGHT and LTα1β2

• Functional readouts:

  • CFU assays to assess stem cell properties

  • RNA-sequencing to analyze transcriptional changes

  • Xenotransplant experiments to evaluate in vivo effects

How should researchers approach bioinformatic analysis of LTBR across multiple datasets?

An integrated bioinformatic approach is recommended:

• Expression analysis using:

  • UCSC-XENA database for uniformly normalized pan-cancer dataset

  • GDC database for copy number variation data

  • CCLE database for tumor cell line expression

  • GTEx database for expression in normal tissues

• Alternative polyadenylation (APA) analysis:

  • APAatlas database to identify APA events across 53 human tissues

• Protein expression verification:

  • Human Protein Atlas (HPA) database for protein expression levels

  • Immunofluorescence staining for subcellular localization

• Clinical correlation analysis:

  • TISIDB database for immune and molecular subtypes analysis

  • Analysis of correlation with immune regulatory genes, checkpoint genes, and immune cell infiltration

How does LTBR function as an immune checkpoint in tumor-associated macrophages?

Recent research identifies LTBR as a novel immune checkpoint in TAMs . Immunosuppressive mechanisms include:

• LTBR activation by T cell-derived LTα1β2 acts as a counterregulatory signal against inflammatory reactions

• LTBR expression is highest in TAMs compared to other immune cells

• LTBR signaling appears to promote tumor-induced suppressive macrophage phenotypes

When investigating this checkpoint function, researchers should:

• Compare LTBR expression in M1 vs. M2 macrophage populations

• Evaluate changes in inflammatory cytokine production upon LTBR blockade

• Assess T cell activation in co-culture systems following LTBR pathway modulation

What is the role of LTBR signaling in leukemia stem cell maintenance and how can it be targeted?

LIGHT/LTBR-signaling is crucial for AML pathogenesis, particularly for LSC maintenance and expansion . Experimental findings show:

• Blocking LTBR signaling through LIGHT-targeting monoclonal antibodies reduces LSC functionality

• LTBR pathway inhibition affects colony formation capacity in vitro

• Secondary transplantation experiments demonstrate reduced leukemia-initiating potential upon LTBR blockade

Therapeutic targeting approaches should focus on:

• Developing LIGHT-targeting monoclonal antibodies with enhanced ADCC activity

• Exploring combination with other LSC-targeting agents

• Investigating potential synergies with conventional chemotherapy regimens

How does LTBR expression correlate with immune infiltration patterns across different cancer types?

LTBR expression shows distinct patterns of correlation with immune cell infiltration across cancer types . Analysis approaches include:

• Correlation analysis between LTBR expression and:

  • Immune regulatory genes

  • Immune checkpoint genes

  • RNA modification genes

  • Immune cell infiltration signatures

• Classification by immune subtypes:

  • C1 (wound healing)

  • C2 (IFN-gamma dominant)

  • C3 (inflammatory)

  • C4 (lymphocyte depleted)

  • C5 (immunologically quiet)

  • C6 (TGF-b dominant)

Researchers should integrate these findings with molecular subtype data for each cancer to develop a comprehensive understanding of LTBR's role in the tumor immune microenvironment.

What methodological approaches should be developed to better understand LTBR's dual role in inflammation and cancer?

Future methodological developments should focus on:

• Spatially-resolved single-cell technologies to map LTBR signaling networks within the complex tumor microenvironment

• Development of conditional knockout models to assess temporal requirements for LTBR in different stages of tumorigenesis

• Identification of biomarkers that predict response to LTBR pathway modulation

• Advanced protein-protein interaction mapping to identify novel partners in the LTBR signaling complex

• Integration of multi-omics data to develop predictive models of LTBR function in different cellular contexts

How might LTBR-targeting therapeutics be developed and evaluated for clinical applications?

Development pathways should include:

• Generation and characterization of humanized antibodies targeting LTBR or its ligands

• Evaluation of pharmacokinetics and pharmacodynamics in relevant preclinical models

• Development of companion diagnostics to identify patients most likely to benefit

• Investigation of rational combination approaches with established immunotherapies

• Assessment of potential toxicities related to LTBR's role in normal lymphoid organ development

What are the key considerations when resolving contradictory findings about LTBR function across different experimental systems?

When reconciling conflicting data, researchers should:

• Carefully evaluate cell type-specific effects - LTBR functions differently in epithelial, stromal, and immune cell populations

• Consider the balance between different LTBR ligands (LTα1β2 vs. LIGHT) in each model system

• Examine genetic background effects, particularly when comparing human and mouse models

• Account for differences in experimental endpoints and readouts

• Evaluate the potential impact of the tumor microenvironment on LTBR signaling outcomes