The A7R34 antibody is specific for mouse CD127, a 60-90 kDa cell surface protein also known as the Interleukin-7 Receptor alpha chain, or IL-7R alpha. CD127 is typically expressed at the cell surface as a heterodimer with the common gamma chain (CD132). This complex acts as the functional receptor for IL-7, a cytokine important in T and B cell development, and in mature T cell homeostasis. A second cytokine known as Thymic Stromal Lymphopoietin (TSLP) also binds to a receptor complex of CD127 and the TSLPR chain to trigger activation of dendritic cells, and is involved in B cell development, allergy and autoimmunity.

The A7R34 antibody may be used as a phenotypic marker for CD127 on immature B cells, on subsets of thymocytes which are double negative (CD4-CD8- ) or single positive (CD4+ or CD8+), and at low levels on mature, peripheral T cells. CD127 is a key marker, when used in combination with CD4 and CD25, to distinguish Treg and effector/memory Treg populations known as T(REM).