IL 16 Human, (130 a.a.)

What is IL-16 Human (130 a.a.) and what are its structural characteristics?

Human Interleukin-16 (IL-16), also known as lymphocyte chemoattractant factor (LCF), is a cytokine primarily secreted by lymphocytes, epithelial cells, eosinophils, and CD8+ T-cells. The 130 amino acid recombinant form represents a specific isoform cleaved from pre-interleukin-16. This protein has a molecular weight of approximately 13.4 kDa and functions as a CD4 receptor ligand .

The protein has three known isoforms derived from pre-interleukin-16 processing. In terms of cross-species homology, human IL-16 shares approximately 85% amino acid sequence identity with murine IL-16, making it highly conserved across mammalian species . This conservation suggests evolutionary importance in immune function.

How does IL-16 signal through cellular receptors and what are the downstream effects?

IL-16 primarily signals through the CD4 receptor on target cells, initiating several distinct cellular responses. These include:

• Induction of IL2Rα expression on T-cells

• Suppression of HIV replication

• Inhibition of T-cell antigen receptor/CD3-mediated T-cell stimulation in mixed lymphocyte reactions

The signaling cascade involves increases in intracellular Ca+ and inositol-1,4,5-trisphosphate in CD4+ T lymphocytes . These biochemical changes lead to functional outcomes including chemotaxis of CD4+ T lymphocytes, monocytes, and eosinophils at nanomolar concentrations. Additionally, IL-16 can induce expression of IL-2R and MHC class II molecules on target cells .

What methodological approaches are recommended for IL-16 storage and experimental use?

For optimal research outcomes, the following handling protocols are recommended:

• Storage: Store desiccated at -20°C to maintain bioactivity

• Reconstitution: Use sterile buffers appropriate for downstream applications

• Purity assessment: Confirm purity (>95%) via SDS-PAGE and HPLC analyses before experimental use

• Source consideration: Recombinant IL-16 is commonly produced in Escherichia coli expression systems

It is critical to note that while IL-16 is used extensively in research, commercially available recombinant products are manufactured for RESEARCH USE ONLY and cannot be used for human consumption or therapeutic applications .

How can researchers effectively measure IL-16 expression in different experimental contexts?

Multiple methodological approaches can be employed to quantify IL-16 expression:

RNA-based detection:

• qRT-PCR using specific primers for IL-16

• RNA extraction using TrizolTM reagent with GlycoBlue® precipitation for enhanced yield

• Standardization using housekeeping genes (e.g., Ppia) and employing the 2-ΔΔCt method for relative quantification

Protein-based detection:

• ELISA for IL-16 in serum samples, tissue homogenates, or cell culture supernatants

• Western blotting for intracellular protein detection

• Immunohistochemistry for tissue localization studies

Systems biology approaches:

• RNA-seq to identify genes correlated with IL-16 expression

• Pathway enrichment analysis to determine biological processes associated with IL-16

Researchers investigating IL-16 in mouse models should collect specimens including serum, lung homogenates, and bronchoalveolar lavage fluid to comprehensively evaluate expression patterns in vivo .

What is the role of IL-16 in viral infections and how can researchers study these interactions?

IL-16 exhibits differential effects across viral pathogens, making it an intriguing target for viral immunology research:

Anti-HIV-1 activity:
IL-16 demonstrates suppressive effects on HIV replication . To investigate this phenomenon, researchers can generate stable human CD4+ T cell transfectants expressing the C-terminal 130 aa of human IL-16, which renders these cells resistant to HIV infection . The mechanism appears to be primarily extracellular, as cells expressing IL-16 linked to a signal peptide secrete considerably more IL-16 and show enhanced resistance to HIV replication (up to 25 days) compared to cells expressing IL-16 without a signal peptide (resistance up to 15 days) .

Pro-Influenza A virus effects:
Contrary to its anti-HIV effects, IL-16 enhances host susceptibility to Influenza A virus (IAV). Experimental data show that IL-16 overexpression facilitates IAV replication, while IL-16 deficiency reduces host susceptibility both in vitro and in vivo . Mechanistic studies reveal that IL-16 inhibits IFN-β transcription and suppresses expression of IFN-β and IFN-stimulated genes .

To study these contrasting effects, researchers should consider the following methodological approaches:

• Gene overexpression and knockdown studies in relevant cell lines

• Measurement of viral load using quantitative PCR

• Assessment of cytokine responses in infected cells and animal models

• In vivo infection models with IL-16 knockout or overexpressing animals

How does IL-16 compare across different species and what are the implications for translational research?

Cross-species homology data provides important considerations for translational research:

• Receptor binding affinity and downstream signaling

• Cell type-specific expression patterns

• Regulatory mechanisms controlling IL-16 processing and secretion

• Interaction with pathogen-specific immune responses

For translational studies, it is advisable to validate key findings in human systems whenever possible, particularly when investigating therapeutic applications or disease-specific mechanisms.

What mechanisms govern IL-16 processing and secretion, and how do they impact biological activity?

IL-16 processing and secretion involve unique pathways that directly impact its biological activity:

Processing pathways:

• IL-16 is encoded as a 631-amino acid precursor lacking a conventional N-terminal signal peptide

• Despite the absence of a signal peptide, IL-16 can be secreted through non-classical pathways

• When engineered with a signal peptide, IL-16 processes through the endoplasmic reticulum-Golgi pathway and undergoes glycosylation

Secretion efficiency:

• Cells expressing IL-16 linked to a signal peptide secrete considerably more protein than cells expressing IL-16 without a signal peptide

• The C-terminal 100 aa (PDZ-like motif) alone, without a signal peptide, results in poor secretion

• Adding a signal peptide to the C-terminal 100 aa restores secretion

Functional implications:

• Secretion appears essential for anti-HIV activity; cells expressing signal peptide-linked IL-16 show resistance to HIV replication for approximately 25 days compared to only 15 days for those without

• The C-terminal 100 aa without a signal peptide confers minimal HIV resistance, while the addition of a signal peptide restores protective effects

Researchers investigating IL-16 function should carefully consider the construct design, particularly regarding the presence or absence of signal peptides, as this significantly impacts secretion efficiency and biological activity.

How does IL-16 influence adipocyte biology and what are the implications for metabolic research?

IL-16 plays complex roles in adipocyte biology with potential implications for obesity and metabolic disorders:

Expression patterns in obesity:

• IL-16 levels are elevated in obesity, particularly in white adipose tissue (WAT)

• Both adipocytes and infiltrated immune cells can secrete IL-16

Effects on adipocyte differentiation:

Impact on mature adipocytes:
IL-16 (10 ng/mL) treatment of mature adipocytes alters multiple metabolic pathways:

• Lipid and glucose metabolism:

  • Decreased expression of Plin1, Cd36, and Glut4

  • Reduced Plin1 may enhance proinflammatory responses

  • Decreased Cd36 may alter fatty acid uptake

  • Reduced Glut4 suggests impaired glucose uptake

• Tissue remodeling and hypoxia:

  • Decreased Hif1a and Vegf expression

  • Enhanced Mmp9 and decreased Timp1 expression, increasing the Mmp9/Timp1 ratio

  • These changes suggest IL-16 could inhibit hypoxia while increasing extracellular matrix remodeling in WAT

Methodological approaches for studying IL-16 in adipocyte biology:

• In vitro differentiation of preadipocytes (e.g., 3T3-L1 cells)

• Oil Red O staining for lipid accumulation assessment

• qRT-PCR for gene expression analysis of differentiation markers, inflammatory mediators, and metabolism-related genes

• Public database analysis (e.g., GEO repository) to identify pathways enriched in genes correlating with IL-16

This research area offers promising avenues for understanding the intersection of immunity and metabolism in obesity-related disorders.

What is the role of IL-16 in cardiovascular pathology and how can researchers investigate these effects?

Emerging evidence indicates that IL-16 may play important roles in cardiovascular pathology, particularly in carotid plaques and stroke risk:

Studies have found associations between high levels of IL-16 in human carotid plaques and cerebrovascular symptoms including stroke, transient ischemic attack, and amaurosis fugax . This suggests IL-16 may serve as a potential biomarker for plaque instability and stroke risk.

Research methodologies for investigating IL-16 in cardiovascular pathology:

• Comparative analysis of IL-16 levels in plaques from symptomatic versus asymptomatic patients

• Correlation of IL-16 expression with markers of plaque stability

• Prospective studies examining the relationship between plaque IL-16 levels and postoperative cardiovascular events

These approaches may yield valuable insights into the role of IL-16 in cardiovascular disease progression and potentially identify new therapeutic targets or prognostic markers.

What are the optimal experimental conditions for studying IL-16 interactions with immune cells?

When designing experiments to investigate IL-16 interactions with immune cells, researchers should consider:

Concentration range:

• Chemotactic effects on CD4+ T lymphocytes, monocytes, and eosinophils are observed at nanomolar concentrations

• For in vitro adipocyte studies, concentrations of 1-10 ng/mL have been used effectively

Functional readouts:

• Migration assays to assess chemotactic activity

• Calcium flux measurements to evaluate receptor signaling

• Gene expression analysis for downstream effects

• Assessment of cell surface marker induction (e.g., IL-2R and MHC class II)

Cell types:

• CD4+ T lymphocytes (primary target)

• Monocytes

• Eosinophils

• CD8+ T cells (primary source)

• Lymphocytes

• Epithelial cells

Potential confounding factors:

• Presence of other cytokines that may synergize with or antagonize IL-16 effects

• Activation state of target cells, which may affect receptor expression

• Species differences when comparing human and mouse systems

How can researchers effectively analyze the impact of IL-16 on gene expression networks?

To comprehensively analyze the impact of IL-16 on gene expression networks, researchers should consider:

Bioinformatic approaches:

• Gene correlation analysis to identify genes whose expression patterns correlate with IL-16

• Pathway enrichment analysis to determine biological processes associated with IL-16

• Cell identity analysis to identify the main cell types expressing genes correlated with IL-16

Analysis of publicly available datasets indicates that IL-16 is associated with several key biological processes:

• Inflammatory processes

• Regulation of cell activation

• Immune system processes

• Adaptive immune response

• Regulation of response to stimulus

• Cell adhesion

• Cell communication

Experimental validation:

• qRT-PCR to verify expression changes in key candidate genes

• Western blotting to confirm changes at the protein level

• Functional assays to validate the biological significance of gene expression changes

By combining bioinformatic analyses with experimental validation, researchers can gain comprehensive insights into the complex regulatory networks influenced by IL-16.

What are the most promising therapeutic applications of IL-16 based on current research?

Based on the diverse biological activities of IL-16, several therapeutic applications warrant further investigation:

Anti-HIV strategies:
The demonstrated ability of IL-16 to suppress HIV replication suggests potential for HIV treatment or prevention strategies. Particularly promising is the finding that cells expressing IL-16 linked to a signal peptide show enhanced resistance to HIV infection . This could inform gene therapy approaches or the development of IL-16-inspired antiviral compounds.

Anti-inflammatory applications in obesity:
Given IL-16's role in adipocyte biology and its elevation in obesity, targeting IL-16 or its downstream pathways might represent a novel approach to mitigating obesity-associated inflammation and metabolic dysfunction .

Cardiovascular disease:
The association between high levels of IL-16 in carotid plaques and cerebrovascular symptoms suggests potential applications as a biomarker for stroke risk or as a therapeutic target for preventing plaque instability .

Antagonistic approaches for influenza infection:
Since IL-16 enhances host susceptibility to influenza A virus infection, IL-16 antagonists might represent a novel strategy for reducing the severity of influenza infections .

Each of these applications requires further research to validate mechanisms, efficacy, and safety before clinical translation can be considered.

What methodological advances would enhance our understanding of IL-16 biology?

Several methodological advances could significantly enhance our understanding of IL-16 biology:

• Development of specific IL-16 isoform antibodies: Tools that can distinguish between different IL-16 isoforms would enable more precise characterization of processing and function

• Single-cell analyses: Applying single-cell RNA sequencing and proteomics to identify cell-specific IL-16 expression patterns and responses

• Advanced imaging techniques: Methods for visualizing IL-16 secretion, trafficking, and receptor binding in real-time could provide insights into its biological activity

• Improved in vivo models: Development of conditional and tissue-specific IL-16 knockout or overexpression models would enable more precise dissection of its role in different physiological and pathological contexts

• Systems biology approaches: Integration of multi-omics data to build comprehensive models of IL-16's position within broader immune and metabolic networks

These methodological advances would address current limitations in IL-16 research and potentially reveal new functions and therapeutic applications.