In Vivo Applications of Clone L243 in Mice

Clone L243 is a mouse monoclonal antibody (IgG2a) that specifically binds to the human HLADR (MHC class II) antigen. While it is primarily designed for human studies, its use extends to certain mouse applications, especially in xenograft or humanized mouse models.

Direct In Vivo Use

Given that L243 is specific to human HLADR, its direct in vivo applications in wildtype mice are limited. Mice express their own MHC class II molecules (IA, IE), not human HLADR, so L243 does not recognize murine MHC class II and cannot be used for immunoprecipitation, cell depletion, or functional blockade in regular mice.

However, L243 can be used in vivo in humanized mouse models—mice engrafted with human cells or tissues expressing HLADR, such as human tumor xenografts or immune system humanized models. In these contexts, L243 can be used for:

• Depletion of HLADR+ cells: Administering L243 in vivo may deplete human antigenpresenting cells (APCs) or tumor cells expressing HLADR, allowing researchers to study the role of these cells in immune responses or tumor progression.
• Functional blockade: L243 can block HLADRmediated antigen presentation, useful for investigating the role of HLADR in human immune cell activation and T cell responses within a humanized mouse context.
• Cell tracking and phenotyping: L243 can be used to analyze the expression and function of human HLADR in engrafted human cells, providing insights into the behavior and differentiation of immune cells in vivo.

Indirect Applications

• Genetic targeting: The variable regions of the L243 antibody have been cloned and used to engineer targeting units for DNA vaccines that direct immunogens specifically to HLADR+ human APCs in transgenic mice expressing human HLADR. For example, scFv derived from L243 has been incorporated into vaccine constructs to enhance antigen presentation in HLADRtransgenic mice, improving immune responses to vaccination.
• Translational research: In studies where human cells or tissues are implanted into mice, L243 can be used to manipulate or assay those human cells in vivo, bridging preclinical and clinical research.

Typical Applications (Primarily In Vitro or Ex Vivo)

• Flow cytometry: Phenotyping and sorting HLADR+ human cells in mouse tissues or blood after xenograft.
• Immunohistochemistry: Detecting human HLADR expression in mouse tissue sections bearing human grafts.
• Western blotting, immunoprecipitation, and immunofluorescence: Analyzing human HLADR protein levels or interactions in samples obtained from humanized mice.

Summary Table

Key Points

• L243 is specific for human HLADR and does not recognize mouse MHC class II, so in vivo applications are restricted to mice bearing human cells or HLADR transgenes.
• Humanized or xenograft mouse models are required for direct in vivo use of L243 in mice, enabling studies on human immune cell depletion, functional blockade, and antigen presentation.
• Genetic targeting with L243derived scFv can be used in transgenic mice expressing human HLADR for vaccine development and immune response studies.
• In vivo applications in regular mice are not possible, but ex vivo and in vitro assays on human cells in mice are common.

In conclusion, clone L243’s main in vivo applications in mice are limited to models where human HLADR is present, such as in humanized or HLADRtransgenic mice. Here, it is used for targeted depletion, functional blockade, and immunological studies of human cells in a murine host.

The most commonly used antibodies and proteins with L243 (antiHLADR) in the literature are other antibodies targeting cell lineage or differentiation markers and functional probes in multiantibody panels, as well as those used in combination therapy research. Most notably:

• AntiCD20 antibodies (e.g., rituximab): Frequently combined with L243, especially in studies of B cell malignancies, due to the physical and functional coupling of CD20 and HLADR on B cells.
• Other antiHLADR clones (e.g., LB3.1): Used as comparators or validation clones in phenotyping and functional assays.
• AntiCD52 (e.g., alemtuzumab): Sometimes used in panel studies for characterizing immune cell populations or as combined therapeutic agents.
• Lym1 and Hu1D10: Alternative antiHLADR antibodies studied in lymphoma and comparative preclinical experiments.
• Cytokines and cytokinecoupled antibodies (e.g., IFNα, IFNαantibody conjugates): Used to investigate additive or synergistic cytotoxic effects with L243, particularly on lymphoma cell lines.
• Cell lineage markers: Antibodies such as antiCD3, antiCD4, antiCD8, antiCD19, and antiCD45 are often included in multiparameter flow cytometry panels with L243 for immune profiling.
• Isotype controls and secondary antibodies: Controls like mouse IgG2a and secondary antibodies (e.g., Alexa Fluorconjugated goat antimouse IgG) are routinely paired with L243 in flow cytometry.

Key applications of these combinations include:

• Multiparameter flow cytometry: For immune subset identification and activation profiling.
• Therapeutic research in Bcell lymphomas: Evaluating combination therapies with rituximab and L243.
• Functional studies: Assessing additive or synergistic effects (e.g., L243 + IFNα).

Other less commonly cited antibodies or proteins:

• LAG3: Protein studied for its direct and specific interaction with HLAclass II heterodimers, occasionally referenced for functional interaction studies with HLADR.
• Negative and positive control antibodies: e.g., MN14 (negative control), A20 (positive control) in cytotoxicity assessments.

In summary, frequently used antibodies/proteins with L243 include antiCD20 (rituximab), other antiHLADR clones, lineage markers (CD3, CD4, CD19), IFNα, and isotype/secondary controls.

Key findings from scientific literature citing clone L243 focus on its specificity, epitope recognition, noncrossreactivity, and broad use in immune profiling of human and nonhuman primate cells:

• Specificity and Epitope: Clone L243 is a mouse monoclonal antibody that binds specifically to a conformational epitope on the HLADR αchain, which is only formed when the α and β chains of HLADR are correctly folded into a heterodimer. This specificity allows for highly reliable detection of native HLADR molecules on cells.

• No CrossReactivity: L243 does not crossreact with other major human MHC class II molecules HLADP or HLADQ, further supporting its high selectivity for HLADR.

• Target and Cellular Expression: The antibody detects HLADR, a key MHC class II molecule, which is constitutively expressed on professional antigenpresenting cells (APCs) including B cells, monocytes/macrophages, and dendritic cells, and can be induced on activated T cells and some epithelial cells.

• Applications: L243 is widely used for:

  • Flow cytometry to identify and quantify HLADR+ cells in blood and tissues.
  • Immunohistochemistry and immunofluorescence for tissue staining.
  • Immunoprecipitation, western blotting, and cell depletion experiments.
  • Blocking mixed lymphocyte reactions in functional immune assays.

• Reactivity Across Species: Clone L243 also crossreacts with HLADR homologs in several nonhuman primate species and in dogs, broadening its utility in comparative and translational immunology research.

• Biological Relevance: Research using L243 has contributed to understanding immune cell phenotyping, clinical assessment of immune activation (e.g., in transplantation, infection, or autoimmune disease), and the role of HLADR in antigen presentation to CD4+ T cells.

• Publications and Impact: L243 is one of the most cited antiHLADR clones in immunology literature, appearing in numerous peerreviewed publications and referenced in diverse experimental contexts.

In summary, clone L243 is a goldstandard antibody for the reliable detection and functional study of HLADR in human and closely related species, with key findings supporting its utility in specific and sensitive immune phenotyping and research on antigen presentation.

The dosing regimens of clone L243, an antibody targeting human HLADR, can vary significantly across different mouse models. There is no universal dosing regimen for L243, as it is highly dependent on the specific experimental question, the degree of HLADR expression, and the type of mouse model being used (e.g., humanized vs. nonhumanized models) .

Key Considerations:

• Mouse Model Type: Different models might require different dosing strategies based on their specific characteristics, such as the presence of human HLADR expression.
• Experimental Context: The dosing regimen should be tailored to the research objective, whether it involves cell depletion, immune modulation, or other purposes.
• Empirical Determination: Researchers typically need to empirically determine the optimal dosing regimen for their specific study, often through trial and error.

Unfortunately, there isn't a standard dosing regimen available for clone L243 across various studies, as each research context is unique. Therefore, titration and optimization of the antibody dose are recommended to achieve the desired experimental outcomes.