HLA-DR Antibody (MHC II) [clone LN3] (V2586)

Description

HLA-DR Antibody (clone LN3) recognizes human HLA-DR, a major histocompatibility complex class II (MHC II) protein essential for antigen presentation to CD4-positive T lymphocytes. HLA-DR is expressed on dendritic cells, macrophages, B cells, and thymic epithelial cells, and can be upregulated on additional cell types during immune activation. Functionally, HLA-DR is a heterodimer consisting of a non-polymorphic alpha chain (DRA) and a highly polymorphic beta chain (DRB), which together form the peptide-binding groove used to present processed extracellular peptides to helper T cells. This antigen presentation pathway plays a fundamental role in adaptive immunity, immune tolerance, and the pathogenesis of autoimmune and inflammatory diseases.

Both HLA-DR chains are type I membrane glycoproteins that assemble in the endoplasmic reticulum with the invariant chain (CD74), which directs them into endosomal compartments for peptide loading. After proteolytic removal of CD74 and editing by HLA-DM, peptide-loaded HLA-DR is transported to the cell surface. Because of its involvement in antigen presentation, HLA-DR serves as a widely used marker of antigen-presenting cell activation in immunohistochemistry, flow cytometry, and tissue immunopathology. Elevated HLA-DR expression is characteristic of activated microglia, inflammatory infiltrates, and certain neoplasms, making it an important readout of immune microenvironment status.

Clone LN3 is a well-established monoclonal antibody that detects a conserved, non-polymorphic HLA-DR epitope. The precise amino acid epitope has not been mapped in the primary literature, but two peer-reviewed findings provide insight into its chain-level specificity. First, a fetal tissue immunohistochemistry study published in the Journal of Histochemistry and Cytochemistry states that LN3 recognizes 'a non-polymorphic portion of the HLA-DR alpha chain' making this the only published chain-specific assignment for LN3. This aligns with the biology of the DRA chain, which is largely non-polymorphic across individuals.

Second, western blot data from a microglial activation study in MPTP-treated primates report that LN3 detects a 29-33 kDa band in human tissues. This observed molecular weight corresponds more closely to the expected migration of the DRB beta chain (~26-28 kDa) than to the somewhat larger DRA alpha chain (~33-36 kDa). The authors did not perform chain-specific immunoprecipitation or mutagenesis, so their data do not contradict the alpha-chain assignment; instead, they suggest that LN3 may recognize an epitope whose conformational or fixation-resistant properties behave differently under denaturing SDS-PAGE conditions. In other words, LN3 identifies a non-polymorphic HLA-DR determinant in situ, while its WB target size falls within the beta-chain range.

Taken together, published findings support that clone LN3 binds a non-polymorphic HLA-DR epitope that has been described as alpha-chain associated in immunohistochemistry, yet produces a western blot band in the beta-chain size range. No peer-reviewed study has performed definitive epitope mapping, and the chain-level specificity of LN3 remains incompletely resolved. Accordingly, LN3 is best characterized as a well-validated pan-HLA-DR antibody whose recognized determinant is conserved across HLA-DR allotypes, with both alpha- and beta-chain evidence present in the literature.

Application Notes

Optimal dilution of the HLA-DR antibody should be determined by the researcher.

1. Staining of formalin-fixed tissues requires boiling tissue sections in 10mM Citrate buffer, pH 6.0, for 10-20 min followed by cooling at RT for 20 min
2. The prediluted format is supplied in a dropper bottle and is optimized for use in IHC. After epitope retrieval step (if required), drip mAb solution onto the tissue section and incubate at RT for 30 min.

Immunogen

Activated human peripheral blood mononuclear cells were used as the immunogen for the HLA-DR antibody.

Storage

Store the HLA-DR antibody at 2-8oC (with azide) or aliquot and store at -20oC or colder (without azide).