CD203

CD203 is a cluster of differentiation designation used in immunophenotyping to refer to certain members of the ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) family. In practice, the CD203 designation most commonly refers to two distinct cell-surface proteins: CD203a (encoded by ENPP1) and CD203c (encoded by ENPP3). The use of CD203 as a single tag is ambiguous; precise identification requires specifying the specific CD number or the enzyme name.

CD203a/ENPP1 is a type II transmembrane glycoprotein with nucleotide phosphodiesterase activity involved in extracellular nucleotide metabolism and signaling. It is broadly expressed on multiple cell types and tissues, contributing to regulation of nucleotide levels in the extracellular space.

CD203c/ENPP3 is primarily expressed on cells of the myeloid lineage, especially basophils and mast cells, where it serves as an activation marker. Upon cellular activation, CD203c expression increases on the cell surface and can be measured by flow cytometry, frequently used in basophil activation testing.

Clinical and research relevance: CD203a and CD203c are used in immunophenotyping and functional assays to study immune cell activation, particularly basophil responses in allergic and inflammatory contexts. Because the CD203 label can refer to more than one molecule, accurate interpretation depends on specifying CD203a or CD203c (or ENPP1/ENPP3) and considering the cellular context.

See also ENPP1, ENPP3, and other CD markers for related immunophenotyping concepts.