IL34 Human

What is the molecular structure of human IL-34?

Human IL-34 is secreted as a homodimer consisting of 39 kDa monomers. It is synthesized as a 242 amino acid precursor that contains a 20 amino acid signal sequence and a 222 amino acid mature chain. The mature chain contains one potential site of N-linked glycosylation. The protein has no structural homology to any known cytokine family despite its functional similarities to CSF-1 . When working with recombinant human IL-34, researchers typically use the Asn21-Pro242 segment with a C-terminal 6-His tag for experimental studies .

How does human IL-34 differ from mouse IL-34?

Human IL-34 shares approximately 71% amino acid sequence identity with mouse IL-34 . This relatively high conservation across species suggests evolutionary importance of the protein's function. When designing cross-species experiments, researchers should consider these structural differences, especially when evaluating receptor binding affinity and downstream signaling events. Species-specific antibodies should be employed for accurate detection in mixed experimental systems.

What are the primary biological functions of IL-34 in human physiology?

IL-34 primarily functions as an alternative ligand for the colony-stimulating factor-1 receptor (CSF-1R). It stimulates monocyte proliferation and promotes the formation of colony-forming unit-macrophage (CFU-M), a macrophage progenitor, in human bone marrow cultures . In functional studies, IL-34 stimulates phosphorylation of extracellular signal-regulated kinase-1 and -2 (ERK1/2) in human monocytes, similar to CSF-1 . IL-34 and CSF-1 both support cell growth and survival of human monocytes and their differentiation into macrophages, though with some differences in polarization and cytokine production profiles .

What is the tissue distribution pattern of IL-34 in humans?

IL-34 is expressed in various human tissues, with particularly high levels detected in the brain and skin where it is produced by neurons and keratinocytes, respectively . It is also expressed in heart, lung, liver, kidney, testes, intestine, thymus, spleen, colon, prostate, and lymph nodes . At the protein level, IL-34 has been detected in human skin, kidney, intestine, spleen, and brain . When designing tissue-specific experiments, researchers should consider these differential expression patterns, as they may indicate tissue-specific functions of IL-34.

How does the expression pattern of IL-34 compare with CSF-1 in human tissues?

Both IL-34 and CSF-1 are broadly expressed across various tissues, but their distribution patterns differ. CSF-1 mRNA is identified in human brain, spleen, testis, kidney, small intestine, lymph nodes, bone marrow, uterus, and ovary . IL-34 shows highest expression in brain and skin, with moderate expression in other tissues . This differential expression suggests that while both cytokines signal through the same receptor (CSF-1R), they may have distinct tissue-specific functions. When studying macrophage populations in specific tissues, researchers should consider analyzing both ligands to understand their relative contributions.

Which receptors does human IL-34 bind to and how does binding affinity compare to other ligands?

Human IL-34 primarily binds to the colony-stimulating factor-1 receptor (CSF-1R), which it shares with CSF-1 . Additionally, IL-34 can interact with alternative receptors: receptor-type protein-tyrosine phosphatase-ζ (PTP-ζ) and syndecan-1 (CD138), though the latter interaction occurs with lower affinity . PTP-ζ is expressed on neural progenitors, neurons, and glial cells in the central nervous system . For comprehensive receptor binding studies, researchers should employ surface plasmon resonance or similar techniques to quantify these differential binding affinities.

How does IL-34 influence microglia development and homeostasis?

IL-34 plays a critical role in microglia development and maintenance in the central nervous system. While CSF-1 is essential for initial microglial development, IL-34 appears to regulate microglial homeostasis in a region-specific manner . In the retina, IL-34 expression by retinal ganglion cells controls the homeostasis of a specific subset of retinal microglia residing in the inner plexiform layer . IL-34 is also expressed by ependymal cells lining the ventricular system and in the choroid plexus, though its influence on choroid plexus macrophages requires further investigation . For studying microglia, researchers should consider brain region-specific analyses when evaluating IL-34 function.

What is the role of IL-34 in Langerhans cell development and function?

Langerhans cells (LCs), the resident mononuclear phagocytes of the epidermis, are mostly derived from fetal liver monocytes and depend on IL-34 for their development and maintenance . IL-34 is produced by keratinocytes in the skin and is essential for LC homeostasis . When studying epidermal immune responses, researchers should consider the critical role of IL-34 in maintaining this specialized dendritic cell population and employ lineage tracing techniques to distinguish LC-specific effects.

What are the optimal conditions for reconstitution and storage of recombinant human IL-34?

Recombinant human IL-34 is typically supplied as a lyophilized protein. For the standard formulation containing BSA as a carrier protein, reconstitution should be performed at 100 μg/mL in sterile PBS containing at least 0.1% human or bovine serum albumin . For carrier-free formulations, reconstitution at 100 μg/mL in sterile PBS is recommended . The product should be stored immediately upon receipt at the recommended temperature, and repeated freeze-thaw cycles should be avoided by using a manual defrost freezer . For long-term stability studies, researchers should aliquot the reconstituted protein to minimize freeze-thaw cycles.

What experimental methods are most effective for studying IL-34 production in human tissues?

For studying IL-34 production in human tissues, researchers can employ a combination of techniques. At the mRNA level, quantitative RT-PCR provides sensitive detection of IL-34 expression patterns. For protein detection, ELISA, Western blotting, and immunohistochemistry are effective methods. Immunohistochemistry is particularly valuable for identifying the specific cell types producing IL-34 within complex tissues . Single-cell RNA sequencing technologies offer higher resolution insights into cell-specific expression patterns. When analyzing IL-34 expression, researchers should consider parallel analysis of CSF-1 expression to understand their relative contributions in specific contexts.

How is IL-34 expression altered in autoimmune and inflammatory diseases?

IL-34 expression is frequently altered in various autoimmune and inflammatory conditions. High expression of IL-34 correlates with disease severity in autoimmune diseases such as Sjögren's syndrome, systemic lupus erythematosus (SLE), psoriasis, and rheumatoid arthritis (RA) . In inflammatory diseases like liver fibrosis, IL-34 levels are also elevated . When studying these disease states, researchers should employ multiplex cytokine analysis to understand IL-34 expression in the context of the broader inflammatory milieu and consider longitudinal sampling to correlate with disease progression.

What is the role of IL-34 in neuroinflammatory and neurodegenerative diseases?

Given its high expression in the brain and importance for microglia, IL-34 plays significant roles in neuroinflammatory and neurodegenerative conditions. In prion disease models, IL-34 deficiency led to accelerated prion protein (PrPSc) deposition and shorter survival, suggesting a protective role . CSF-1R mutations associated with neurodegenerative diseases like adult-onset leukoencephalopathy with axonal spheroids and pigmented glia may involve disrupted IL-34 signaling . For studying neuroinflammatory conditions, researchers should consider region-specific analysis of IL-34 expression and microglia phenotypes using both imaging and flow cytometry approaches.

How do the functional outcomes of IL-34 versus CSF-1 stimulation differ in human monocytes?

Though IL-34 and CSF-1 both signal through CSF-1R, they induce somewhat different functional outcomes in human monocytes. Both cytokines support monocyte survival and differentiation into macrophages, but IL-34 stimulation leads to higher production of IL-10 and CCL17, while CSF-1 induces greater MCP-1 expression . IL-34–stimulated macrophages also produce more eotaxin-1 compared to CSF-1–stimulated cells . These differential effects suggest distinct signaling mechanisms or receptor conformational changes induced by each ligand. For comparative studies, researchers should design time-course experiments with careful cytokine profiling to capture these differences.

How can single-cell technologies advance our understanding of IL-34 function?

Single-cell technologies like scRNA-seq, mass cytometry, and multiparameter flow cytometry can provide unprecedented insights into IL-34 biology . These approaches can reveal cell-specific expression patterns of IL-34 and its receptors, identify previously unknown cellular sources or targets of IL-34, and characterize the heterogeneity of cellular responses to IL-34 stimulation. When employing these technologies, researchers should include comprehensive panels of markers to identify rare cell populations and consider spatial transcriptomics to maintain information about tissue architecture and cellular interactions.