Anti-Human CD307e (FcRL5) [Clone 509F6] — Purified in vivo GOLD™ Functional Grade

Clone 509F6 is a mouse monoclonal antibody that specifically targets human CD307e (FcRL5) and is used primarily for in vivo and in vitro research applications involving human B cells in mouse models. In vivo applications in mice include:

• Functional blocking studies: The antibody is used to block human FcRL5 function, allowing researchers to study its role in B-cell development, differentiation, and pathogenesis of B-cell malignancies, such as multiple myeloma and lymphoma.
• Xenograft models: In mouse models engrafted with human cells (e.g., human B-cell tumors), 509F6 has been applied for monitoring and manipulating human B-cell populations by targeting FcRL5, a marker notably upregulated in certain B-cell malignancies.
• Flow cytometry and depletion studies: Though primarily a flow cytometry reagent, 509F6 can also be used in vivo for detecting, isolating, or potentially depleting FcRL5+ human B cells in mice, provided the mice bear human immune cells or tumors.

Important limitations and context:

• 509F6 is specific to human FcRL5 and does not cross-react with mouse FcRL5 or FcRL4. Its in vivo applications in mice are limited to humanized or xenograft models expressing the human target.
• Common research uses include studying the biology of human B-cell tumors in mouse xenograft models, testing new CAR-T therapies targeting FcRL5, and elucidating the role of FcRL5 blockade in immune regulation and cancer treatment.
• For in vivo work, the antibody is provided in low-endotoxin, carrier-free formulations suitable for animal studies to minimize immunogenicity and prevent toxicity.

There is no evidence clone 509F6 is directly used to target mouse B cells in wild-type mice, as its specificity is limited to the human FcRL5 protein.

The monoclonal antibody 509F6, which targets CD307e (FcRL5), is most commonly used in the literature alongside antibodies or proteins that identify or characterize B cell populations. The most frequently paired antibodies are:

• CD19: A pan-B cell marker.
• CD27: A marker for memory B cells.
• CD21: Used to define B cell subsets such as naive, memory, and marginal zone B cells.
• LAIR-1: Sometimes included for detailed immunophenotyping of B cell subsets.

These antibodies are typically used together in multicolor flow cytometry panels to distinguish various B cell subsets, including naive B cells, memory B cells, and plasma cells. For example:

• A typical staining panel to study FcRL5 expression might include CD19 (APC-conjugated), CD27 (FITC-conjugated), and 509F6 (often PE-, APC-, or eFluor 660-conjugated).
• Some studies use CD21 (often as PE-Cy7), and occasionally LAIR-1 (PE), in addition to CD19 and CD27, alongside 509F6 for deeper phenotyping.
• Anti-immunoglobulin markers (such as anti-IgG, anti-IgA) may also be included, especially if plasma cell or memory B cell isotype-specific analysis is important.

Additional notes:

• 509F6 is not usually used alone; it is almost always included in panels with other B-lineage and differentiation markers to provide context for FcRL5 expression.
• Studies investigating function may also include blocking experiments with specific Fc fragments or aggregated IgG, since FcRL5 binds to immunoglobulins.
• In sorting or enrichment protocols, magnetic beads conjugated to anti-APC or anti-PE can be used to isolate populations stained with 509F6 and fluorophore-conjugated B cell markers.

Summary of common combinations:| Marker | Use/Subset Identified | Common Fluorochromes Used ||----------|-------------------------------------|----------------------------|| CD19 | Total B cells | APC, APC-Cy7 || CD27 | Memory B cells | FITC || CD21 | Naive/memory/marginal zone B cells | PE-Cy7 || LAIR-1 | B cell regulation studies | PE |

These combinations are widely reported in leading immunology journals and antibody manufacturer data sheets.

Key Findings Related to Clone 509F6 in Scientific Literature

Clone 509F6 is a monoclonal antibody targeting human FcRL5 (also known as CD307e, FcRH5, or IRTA2), a transmembrane glycoprotein expressed predominantly on B cells, especially malignant B cells. Below are the key findings associated with this clone as reported in peer-reviewed research and product literature.

FcRL5 as a Biomarker in B Cell Malignancies

• Abnormal FcRL5 Expression in B Cell Cancers: Clone 509F6 has been instrumental in demonstrating aberrant FcRL5 expression in a variety of B cell malignancies, including multiple myeloma, chronic lymphocytic leukemia (CLL), mantle cell lymphoma, and hairy cell leukemia.
• Diagnostic and Prognostic Potential: Elevated levels of both surface-bound and soluble FcRL5 have been detected in patients with these cancers, suggesting FcRL5 may serve as a useful biomarker for diagnosis and potentially for monitoring disease progression.
• Selective Expression: FcRL5 is differentially expressed in the B cell lineage, with little expression on peripheral blood cells but high expression on plasma cells and certain leukemias/lymphomas.

Functional Insights

• Binding and Blocking: mAb 509F6 binds to an epitope within the first three Ig domains of FcRL5 and is capable of blocking FcRL5's interaction with all aggregated IgG isotypes. This has implications for understanding FcRL5’s role in immune complex regulation.
• Inhibitory Coreceptor Role: FcRL5 functions as an inhibitory coreceptor on mature B cells by recruiting the phosphatase SHP-1 to its intracellular ITIM motifs, modulating B cell signaling.
• Biochemical Characteristics: FcRL5 is a type I transmembrane glycoprotein with nine extracellular Ig domains, an ITAM-like sequence, and two ITIM-like sequences, and is homologous to FcγR1 (CD64).

Therapeutic Applications

• Target for Immunotherapies: Given its high and selective expression on malignant B cells, FcRL5 has emerged as a therapeutic target. Chimeric antigen receptor (CAR) T cells targeting FcRL5 have shown potent anti-myeloma activity in preclinical models, inhibiting tumor growth and prolonging survival in mouse xenograft models of multiple myeloma.
• Combination Therapy Potential: FcRL5/BCMA dual-targeted CAR-T cells demonstrated enhanced anti-tumor effects and longer median survival compared to single-target therapies in preclinical studies.
• Clinical Relevance: The ability of clone 509F6 to detect and block FcRL5 supports its use in both diagnostic applications and as a tool to validate FcRL5 as a target for novel immunotherapies.

Technical Use in Research

• Flow Cytometry and Immunofluorescence: Clone 509F6 is widely used in flow cytometry to detect FcRL5 expression on cells, including transfectants and primary B cells.
• Immunoprecipitation and Blocking Assays: The antibody is also used in immunoprecipitation and functional blocking assays to study FcRL5 interactions.

Summary Table: Key Attributes of Clone 509F6

In summary, clone 509F6 has been central to uncovering FcRL5’s role as a biomarker and therapeutic target in B cell malignancies, provided critical tools for functional studies, and supported the development of novel immunotherapies such as FcRL5-targeted CAR-T cells.

Dosing regimens of clone 509F6 (anti-human CD307e/FcRL5) are not standardized across different mouse models, and there is a lack of published, universally accepted dosing protocols for in vivo use in mice. Most literature and vendor datasheets describe the antibody primarily for in vitro applications such as flow cytometry or blocking assays, but do not provide detailed dosing strategies for in vivo administration.

Key context:

• 509F6 is a mouse monoclonal antibody specific for human FcRL5 (CD307e), commonly used to block FcRL5 or detect it on human B cells.
• In most published work, 509F6 is used for in vitro blockade or detection at 5 μl per million cells in flow cytometry, with no standard in vivo (e.g., mouse model) dose published.

Available in vivo information:

• Vendor sources for in vivo-grade 509F6 indicate that "dosing regimens ... are not standardized across studies, and detailed dosing protocols specific to in vivo applications are not broadly available".
• No primary literature returned by the search clearly documents specific dosing amounts, frequency, or routes for 509F6 in mouse models.

Supporting details and typical context for similar antibodies:

• Experimental antibodies used in vivo to target human molecules in mice—often in xenograft models or humanized mice—commonly follow dosing strategies similar to other mouse IgG2a anti-human antibodies (often 100–250 μg per mouse, intraperitoneally, every 3–4 days), but this is an extrapolation from anti-CTLA-4, anti-CD40, and other functional antibodies for murine targets.
• However, there is no direct evidence that 509F6 has been dosed this way in published mouse studies—the only verified use in the search results is for in vitro detection or blockade.

Summary of findings:

• There is no published, standardized in vivo dosing regimen for clone 509F6 across mouse models.
• All available protocols are for in vitro use; in vivo use would require empirical optimization.
• When adapting for in vivo, regimens used for similar antibodies might serve as a starting point, but this should be stated as a hypothesis and not an evidence-backed guideline.

If precise dosing for in vivo use is required, empirical titration in pilot studies is recommended, and consultation of any newly published literature or direct communication with the antibody suppliers is advised.