Anti-Human HLA-DR (MHC Class II) [Clone L243] — Purified in vivo PLATINUM™ Functional Grade

Clone L243 is a mouse monoclonal antibody specific for human MHC class II HLA-DR molecules and is widely used to study human cells in mice that express human HLA-DR transgenically, as standard mice do not express human HLA-DR and L243 does not cross-react with mouse MHC class II.

Common in vivo applications of clone L243 in mice include:

• Detection and characterization of human HLA-DR-expressing cells in humanized or transgenic mouse models, often via flow cytometry, immunohistochemistry, or immunofluorescence.
• Functional manipulation of human HLA-DR+ cells in these mice, such as depletion or in vivo blocking, to study immune responses or antigen presentation.
• Targeting human HLA-DR for antigen delivery in vivo, including DNA vaccines that use single-chain variable fragment (scFv) units derived from L243 to direct immunogens to human HLA-DR on antigen-presenting cells; these approaches have generated robust immune responses in mice expressing human HLA-II molecules.
• In vivo studies of human immune cell engraftment, distribution, or activation in humanized mouse models, where L243 can monitor or manipulate HLA-DR+ cells.

Important context and limitations:

• L243 is not reactive with endogenous murine MHC-II, so its in vivo use in mice is limited to models expressing human HLA-DR, such as:
  • Human immune system-engrafted mice (humanized mice)
  • Mice transgenic for human HLA-DR alleles.
• In wild-type mice, L243 has no binding or functional role; most reported in vivo uses rely on engineered expression of the human target.

Other key research applications (in vitro and in vivo):

• Flow cytometry for immune cell phenotyping.
• Immunohistochemistry to locate HLA-DR+ cells in tissues.
• In vivo or ex vivo depletion/blocking of HLA-DR+ cells, e.g., in immune modulation or transplantation studies.
• Immunoprecipitation and Western blotting for protein analysis.

In summary:
Clone L243 is used in vivo in mice primarily to study or manipulate human HLA-DR+ cells in humanized or transgenic mouse models, with common applications including detection, cell depletion or blocking, and antigen targeting for vaccine research. Standard laboratory mice without human HLA-DR expression are not suitable for in vivo applications of L243.

Commonly used antibodies and proteins with L243 (anti-HLA-DR) in the literature include:

• Anti-CD20 antibodies such as rituximab, due to the physical and functional association of CD20 and HLA-DR on B cells.
• Other anti-HLA-DR clones, specifically LB3.1 and LN3, which are used in comparative or multiplex assays with L243, as they bind different epitopes on HLA-DR and do not cross-block each other.
• Lym-1, another anti-HLA-DR antibody used with rituximab and L243 in studies on lymphoma cell lines.
• Cell lineage markers commonly found in multicolor flow cytometry or immunophenotyping panels, such as CD3 (for T cells), CD19 and CD20 (for B cells), and CD14 (for monocytes).
• Functional probes, including markers for dendritic cells, monocytes, and macrophages, reflecting the broader use of L243 in antigen-presenting cell characterization.
• Checkpoint or immunomodulatory antibodies, such as anti-PD-L1 or IDO inhibitors, in the context of combination immunotherapies.

Other relevant details:

• L243 is primarily used for detecting HLA-DR expression in flow cytometry, immunoprecipitation, Western blotting, and functional assays focused on immune cell characterization.
• In spatial biology or multiplex imaging, L243 may be used alongside additional probes for cellular context in tissue sections.

In summary, L243 is most often paired with rituximab, lineage markers (e.g., CD3, CD20), other anti-HLA-DR clones (LB3.1, LN3), and immunomodulatory antibodies, particularly in studies of B cell malignancies, immune profiling, and therapeutic combination strategies.

Clone L243 is a widely used monoclonal antibody in scientific research, particularly for the identification and study of HLA-DR, a human major histocompatibility complex (MHC) class II cell surface molecule. The main findings and applications associated with its citations in the literature are as follows:

• Specificity and Epitope Recognition:

  • L243 binds specifically to HLA-DR, recognizing a conformational epitope on the alpha chain (DRA) of the HLA-DR molecule.
  • It shows no cross-reactivity with other class II molecules such as HLA-DP or HLA-DQ.
  • The recognized epitope depends on the correct folding of the DR αβ heterodimer.

• Research Applications:

  • Widely cited (dozens of publications), L243 is used in flow cytometry, immunoprecipitation, Western blotting, immunohistochemistry, and immunofluorescence.
  • It is commonly employed to identify antigen-presenting cells (e.g. B cells, monocytes, dendritic cells) in human immune profiling and to monitor MHC class II expression in a variety of disease and transplantation settings.
  • L243 enables functional studies, such as blocking mixed lymphocyte reactions and depleting MHC class II-positive cells in experimental models.

• Functional Insights from Patent Literature:

  • Humanized forms of L243 retain specific binding to HLA-DR and have been used to characterize binding affinity, with dissociation constants in the nanomolar range (K_D ~2.6–14 nM), indicating high affinity.
  • L243 does not induce complement-mediated cytotoxicity, making it suitable for assays where cell preservation is important.

• Species Reactivity:

  • While primarily human-specific, L243 also cross-reacts with HLA-DR-like molecules in some non-human primates but not with mouse or rodent MHC class II.

• Notable Literature Citations:

  • Citations include studies on immune regulation, antigen presentation, autoimmunity, infectious disease, and transplantation.
  • It is highly cited in both fundamental and clinical research for distinguishing antigen-presenting populations and tracking immune responses.

• Summary Table of Clone L243 Key Properties

These findings underscore the importance of L243 as a robust tool for basic and translational immunology, serving as a gold standard for delineating HLA-DR expression and function in human systems.

Dosing regimens of clone L243, an antibody specific for human HLA-DR, vary widely across mouse models and must be established empirically because no standard protocol exists that applies to all contexts.

Key details:

• Model Dependence: The regimen depends on the mouse model used (e.g., conventional, immunodeficient, or humanized mice). Humanized models expressing human HLA-DR are typically required for in vivo efficacy, as L243 is specific for human antigens and does not cross-react with murine HLA analogs.
• Route and Schedule: Intravenous and intraperitoneal routes are most common, with dosing frequency and dose size determined by the experimental goals, such as depletion, blocking, or detection of HLA-DR+ cells.
• Empirical Optimization: Factors influencing the dosing include:
  • Extent of HLA-DR expression in the model,
  • Purpose of the experiment (e.g., cell depletion, immune modulation, or imaging),
  • Animal characteristics (age, strain, immune reconstitution status in humanized models).
• Examples from Related Antibodies: While no universal dose is cited for L243, antibody dosing in mouse models (for various targets) ranges from 50–500 μg per injection, administered 1-3 times per week depending on pharmacodynamic and pharmacokinetic considerations. For cell-depleting antibodies, 100–250 μg per mouse per dose is common, but specific L243 studies should determine optimal regimens based on preliminary titration and pilot experiments.

Summary Table: Key Variables Affecting L243 Dosing in Mice

• No published studies or vendors specify a one-size-fits-all L243 regimen; researchers must perform small-scale titrations to determine optimal doses for their specific mouse model and research question.
• For clinical or translational relevance, doses may be further adjusted based on intended human equivalency or preclinical toxicity assessment.

In summary, L243 dosing in mice must be empirically optimized for each experiment, guided by model choice, target HLA-DR expression, and experimental endpoint. No standard regimen exists due to variability in mouse model systems and research aims.