CD19 (Leu12, B-Lymphocyte Antigen B4)

CD19 (cluster of differentiation 19), also known as Leu-12 or B-lymphocyte antigen B4, is a transmembrane protein virtually expressed on the surface of all B lineage cells and follicular dendritic cells. In human B cells, CD19 plays a major regulatory role in B cell differentiation, proliferation and antibody production. Since CD19 is ubiquitously expressed during all phases of B cell development until it is lost on terminal differentiation to plasma cells, it can serve as a reliable biomarker for B lymphocytes and can potentially be used as a diagnostic tool for identifying lymphoma subtypes.

CD19 Structure

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CD19 is a 95 kDa, type I transmembrane protein and member of the immunoglobulin (IgG) superfamily. It consists of three components: a single transmembrane domain, a cytoplasmic C-terminus and an extracellular N-terminus. The cytoplasmic C-terminus, approximately 242 amino acids long, contains nine tyrosine residues, three of which - Y391, Y482, and Y513 - are essential for CD19 functionality. Studies have shown that substitution of phenylalanine for tyrosine at the Y482 and Y153 residues, promotes inhibition of phosphorylation at the remaining seven tyrosine residues. The extracellular N-terminus region consists of two C2 IgG domains that are separated by a small non-IgG domain, as well as, N-linked carbohydrate addition sites.

CD19 Function

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In human B cells, CD19 has two primary functions in B cell activation. It can operate as an adaptor protein in complex with the B cell receptor (BCR) and other surface molecules. Jointly, these elements facilitate both the direct and indirect recruitment and binding of various protein kinases that are necessary for immune cell signaling and B cell act. These include the Src family (Lyn and Fyn), Ras family, adapter molecules, Abl, Btk and PI3K. Additionally, CD19 functions as the major signaling component of the CD19-CD21-CD81-CD225 complex, that is expressed on the surface of mature B cells. As a co-receptor for BCR signal transduction, CD19 can enhance signaling through the BCR and reduce the threshold required for B cell activation following antigen recognition.

CD19 Antibodies

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Monoclonal CD19 antibodies, designed to recognize human CD19 surface molecules, are frequently used in flow cytometry and immunofluorescence applications to identify immune cell subsets expressing CD19. Cells known to express CD19 surface markers include all B lineage cells and follicular dendritic cells. Additionally, malignant tumors of the B lymphocyte system express CD19 at elevated levels; this includes approximately 80% of acute lymphoblastic leukemia, 88% of B cell lymphomas and 100% of B cell leukemia.

AAT Bioquest offers a comprehensive catalog of CD19 antibodies purified by affinity chromatography and conjugated to a variety of fluorophores under optimal conditions that minimize unconjugated fluorophore and antibody. Available fluorophores include:

• iFluor® dyes - bright, photostable dyes with optimized flow cytometry (FACS), fluorescence imaging and in vivo imaging applications.
• mFluor™ dyes - bright, photostable dyes with optimized for flow cytometry (FACS) applications.
• Alexa Fluor^® dyes - suitable for flow cytometry (FACS) and fluorescence imaging applications.
• Classic dyes - suitable for flow cytometry (FACS) and fluorescence imaging applications.
• Phycobiliproteins and Tandem dyes - intensely bright dyes for flow cytometry (FACS) and multiparametric analysis.

1. FC = Flow Cytometry; ELISA = Enzyme-linked immunosorbent assay; IF = Immunofluorescence; IHC-F = Immunohistochemistry (Frozen); WB = Western Blot.

iFluor® Dyes Labeled to CD19 Antibodies

The following table outlines the fluorescence properties of available iFluor® dye labeled anti-human CD19 antibodies for use in flow cytometry (FACS) and fluorescence imaging applications. Conjugates made with iFluor® dyes exhibit superior brightness and photostability, outperforming Alexa Fluor^® conjugates and other spectrally similar conjugates. For additional information on iFluor® dye-labeled CD19 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 260 nm is the correction factor used for eliminating the dye contribution to the absorbance at 260 nm (for oligo and nucleic acid labeling).
4. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

mFluor™ Dyes Labeled to CD19 Antibodies

The following table outlines the fluorescence properties of available mFluor™ dye labeled anti-human CD19 antibodies for use in flow cytometry (FACS). Each mFluor™ dyes is optimally excited by one of the major laser lines commonly equipped in flow cytometers, such as the 405 nm, 488 nm, 532 nm, 561 nm or 633 nm laser lines. For additional information on mFluor™ dye-labeled CD19 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 260 nm is the correction factor used for eliminating the dye contribution to the absorbance at 260 nm (for oligo and nucleic acid labeling).
4. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

Alexa Fluor^® Dyes Labeled to CD19 Antibodies

The following table outlines the fluorescence properties of available Alexa Fluor^® dye labeled anti-human CD19 antibodies for use in flow cytometry (FACS) and fluorescence imaging applications. For additional information on Alexa Fluor^® dye-labeled CD19 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

Classic Dyes Labeled to CD19 Antibodies

The following table outlines the fluorescence properties of available classic dye labeled anti-human CD19 antibodies for use in flow cytometry (FACS) and fluorescence imaging applications. For additional information on classic dye-labeled CD19 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).
2. Φ = fluorescence quantum yield in aqueous buffer (pH 7.2).
3. CF at 280 nm is the correction factor used for eliminating the dye contribution to the absorbance at 280 nm (for peptides and protein labeling).

PE, APC, PerCP and Tandem Dyes Labeled to CD19 Antibodies

The following table outlines the fluorescence properties of available phycoerythrin (PE), allophycocyanin (APC), PerCP and tandem dye labeled anti-human CD19 antibodies for use in flow cytometry (FACS). Phycobiliproteins are uncharacteristically bright due to their high molar extinction coefficients and quantum yields, an enviable quality when imaging low-abundance targets. However, since phycobiliprotiens photobleach rapidly, they are not recommended for microscopy. For additional information on phycobiliprotein-labeled CD19 antibodies and availability of other clones click on any label in the table below.

1. ε = molar extinction coefficient at their maximum absorption wavelength (Units = cm^-1M^-1).

References

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1. Carter, R.H., Wang, Y. & Brooks, S. Role of CD19 signal transduction in B cell biology. Immunol Res 26, 45-54 (2002). https://doi.org/10.1385/IR:26:1-3:045
2. Del Nagro, C.J., Otero, D.C., Anzelon, A.N. et al. CD 19 function in central and peripheral B-cell development. Immunol Res 31, 119-131 (2005). https://doi.org/10.1385/IR:31:2:119
3. Depoil, D., Fleire, S., Treanor, B. et al. CD19 is essential for B cell activation by promoting B cell receptor-antigen microcluster formation in response to membrane-bound ligand. Nat Immunol 9, 63-72 (2008). https://doi.org/10.1038/ni1547
4. R. H. Scheuermann & E. Racila (1995) CD19 Antigen in Leukemia and Lymphoma Diagnosis and Immunotherapy, Leukemia & Lymphoma, 18:5-6, 385-397, DOI: 10.3109/10428199509059636
5. Wang, K., Wei, G., & Liu, D. (2012). CD19: a biomarker for B cell development, lymphoma diagnosis and therapy. Experimental hematology & oncology, 1(1), 36. https://doi.org/10.1186/2162-3619-1-36