Anti-Rat Kappa Light Chain (Clone MAR 18.5) – Purified in vivo PLATINUM™ Functional Grade

Clone MAR 18.5 is commonly used in in vivo mouse applications to deplete or target cells and antibodies of rat origin that have been administered to mice, primarily by binding the rat kappa immunoglobulin light chain. The most frequently described applications are related to depletion protocols and immune cell manipulation.

Key in vivo applications include:

• Depletion of rat antibodies or cells: MAR 18.5 is used to clear rat monoclonal antibodies or cells previously introduced into mice, especially in experimental setups where such depletion is necessary to study the downstream effects of antibody or cell removal.
• B cell depletion: It can be used in combination with anti-CD19 and anti-CD22 monoclonal antibodies (e.g., clones 1D3 and Cγ34.1) to specifically deplete B cells in mice that have been treated with rat-origin reagents.
• Secondary antibody for cross-linking: In studies of Fcγ receptor-mediated phagocytosis or other immune cell functions, MAR 18.5 serves as a secondary antibody to cross-link primary rat-origin antibodies, allowing for targeted stimulation or depletion of certain immune cell populations in vivo.
• Facilitation of functional immunoassays: While its main in vivo use is depletion, MAR 18.5 is also used in ELISA, ELISPOT, flow cytometry (FC), immunofluorescence (IF), immunohistochemistry (IHC), and western blotting (WB) to monitor or manipulate rat immunoglobulin levels in mouse models, though these are primarily ex vivo or in vitro extensions of in vivo studies.

In summary, the primary in vivo role of MAR 18.5 in mice is as an anti-rat kappa light chain monoclonal antibody for depletion of rat antibodies or B cells, especially when rat monoclonal antibodies are used as part of experimental protocols in mouse models.

MAR 18.5 is frequently used in combination with several other antibodies and proteins in research applications, particularly for B cell depletion and immunological studies.

B Cell Depletion Studies

The most common application involves combining MAR 18.5 with anti-CD19 and anti-CD22 antibodies for in vivo B cell depletion in mice. This combination enhances the specificity and durability of immune cell depletion protocols. The specific clones commonly referenced for these antibodies include 1D3 for CD19 and Cγ34.1 for CD22.

T Cell and Antigen-Presenting Cell Studies

MAR 18.5 is frequently co-used with antibodies targeting various T cell and antigen-presenting cell markers, including:

• J11d.2 (anti-heat-stable antigen)
• 2.43 (anti-CD8)
• M5/114 (anti-class II)
• 2.4G2 (anti-FcγR)

These combinations have been employed for T cell isolation and complement lysis studies.

Fcγ Receptor-Mediated Studies

In research examining Fcγ receptor-mediated phagocytosis, MAR 18.5 serves as a secondary cross-linking antibody during macrophage stimulation experiments. In these studies, it is used alongside the 2.4G2 antibody, which targets FcγR receptors. The 2.4G2 antibody appears particularly important in functional assays involving Fc receptors and complement.

The versatility of MAR 18.5 in combination with these various antibodies makes it a valuable tool for studying B cell biology, immune cell interactions, and antibody-mediated cellular processes in rodent models.

Overview of MAR 18.5

Clone MAR 18.5 is a monoclonal antibody specific to the rat kappa (κ) immunoglobulin light chain, binding both RI-1a and RI-1b allotypes. Generated by immunizing SJL/J mice with soluble rat immunoglobulin and fusing immune spleen cells with the P3X63Ag8 myeloma, MAR 18.5 secretes an IgG2a κ antibody that strongly binds protein A.

Key Scientific Findings and Applications

Antibody Specificity and Binding

• MAR 18.5 is highly specific for the rat κ light chain and does not distinguish between RI-1a and RI-1b allotypes.
• It can be used in a variety of applications, including depletion, ELISA, ELISPOT, flow cytometry (FC), immunofluorescence (IF), immunohistochemistry (IHC), and immunoprecipitation (IP).

In Vivo Depletion Strategies

• B Cell Depletion: MAR 18.5 is routinely used in combination with anti-CD19 and anti-CD22 antibodies to achieve efficient in vivo B cell depletion in mice. This is a widely cited protocol in immunological research for studying B cell biology and immune responses.
• Neutrophil Depletion: Recent studies have demonstrated that combining MAR 18.5 with anti-Ly6G antibodies creates a “Combo” approach that achieves durable and controlled neutrophil depletion in mice. This is particularly notable because anti-Ly6G alone is not always sufficient for robust depletion, especially in certain mouse strains and in aged animals. The Combo significantly lowers neutrophil prevalence in blood and tissues compared to anti-Ly6G alone.
• Antigen Masking: A technical challenge in cell depletion is antigen masking by therapeutic antibodies, which can block detection antibodies. Intracellular staining for Ly6G (a neutrophil marker) has been validated as a sensitive workaround in animals treated with anti-Ly6G + MAR 18.5, enabling accurate assessment of neutrophil populations despite surface antigen blockade.

Other Research Applications

• Macrophage Stimulation: MAR 18.5 has been employed as a secondary cross-linking antibody in studies of Fcγ receptor-mediated phagocytosis in macrophages.
• T Cell Isolation: In combination with other antibodies (J11d.2, 2.43, M5/114, 2.4G2), MAR 18.5 has been used for T cell isolation and complement lysis protocols.

Summary Table: Major Uses of MAR 18.5 in Scientific Literature

Notable Technical Details

• Isotype: Mouse IgG2a κ.
• Binding: Strong affinity for protein A, useful for purification.
• Genetics: The κ light chain is encoded by V, J, and C gene segments, undergoing V(D)J recombination for antibody diversity.

Conclusion

Clone MAR 18.5 is a versatile tool in immunology, primarily recognized for its role in in vivo B cell and neutrophil depletion strategies. Its combination with lineage-specific antibodies enables precise and durable immune cell depletion, while its specificity and robustness support a wide array of in vitro and in vivo applications.

Dosing regimens for clone MAR 18.5 (anti-rat kappa light chain) in mouse models are not fully standardized and can vary depending on the experimental application, the mouse strain, and the antibodies being targeted. The most commonly cited regimen is 50 μg per mouse, typically administered intraperitoneally (i.p.), but precise protocols are often tailored to the specific goals and model of the study.

Key context and details:

• Variability: There is no universal dosing schedule for MAR 18.5 in mice; published sources rarely specify a regimen applicable to all contexts. Factors influencing dosing include the mouse strain, experimental endpoint (e.g., immune cell depletion vs. detection), and whether MAR 18.5 is being used as a depleting or blocking antibody.
• Frequently Used Dose: The most frequent dose found in protocols is 50 μg per mouse i.p., but some researchers may adjust this based on their specific protocol or desired degree of depletion/blockade.
• Example Applications: In models aiming for depletion or blocking of rat-derived antibodies or immune components (such as with anti-Ly6G), MAR 18.5 is often given together with other antibodies, and researchers may increase the dose or frequency to achieve robust depletion.
• Administration Route: Intraperitoneal injection is the standard, but intravenous routes can be employed for some protocols, especially if rapid effects are desired.
• Lack of Fixed Schedule: Unlike widely used checkpoint blockade or depletion antibodies (such as anti-CD4, GK1.5, or anti-CD8, 2.43 clones), for which standardized doses and schedules exist (e.g., 200–250 μg per mouse, 2–3× per week), MAR 18.5 dosing is less codified and often determined empirically.

Additional background:

• Mouse Strain Influence: Immunocompetent vs. immunodeficient strains may have different tolerances or responses, and dosing may be modified accordingly—though specific published numbers for different strains are rare.
• Combination with Other Antibodies: In studies where MAR 18.5 is combined with anti-mouse or anti-rat IgG to enhance cell depletion (e.g., neutrophil depletion models), regimens can be adjusted for maximum efficacy.

Summary Table: Typical MAR 18.5 Dosing Practices in Mouse Models

There are no broadly published regimens specifying variations by mouse strain, so researchers should consult the literature for their specific experimental context and adjust dosing based on preliminary results.

If you need more precise protocols for a particular mouse model or research goal, it is recommended to refer to published studies using MAR 18.5 under conditions similar to your own or to run preliminary dose-finding experiments.