The monoclonal antibodies TH6 and 12A5 recognize Folate Receptor 4 (FR4), also known as the membrane folate-binding protein 3 (FBP3). FR4 is a heavily glycosylated 35 kD receptor expressed exclusively in lymphoid tissue and an isoform of the family of receptors that recognize the essential nutrient folic acid. Natural T regulatory cells constitutively express high levels of FR4. Differential expression of FR4 in combination with CD25 can distinguish four functionally distinct CD4+ T cell subpopulations; Natural Tregs, effector T cells, memory-like T cells and Naïve T cells. FR4hi CD25+ expressing CD4+ T cells also express high amounts of Foxp3, GITR and CTLA-4.
Monoclonal antibody TH6 and 12A5 stained CD25+CD4+ T cells at a higher level than other CD4+ or CD8+ T cells. In addition, in vivo injection of TH6 monoclonal antibody reduced the number of CD25+CD4+ T cells and CD25-CD4+ T cells in peripheral blood. Clone 12A5 has been demonstrated to work in western blot. Clones TH6 and 12A5 do not block one another in a flow cytometric assay.
The antibody was conjugated to BD Horizon™ BUV496 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 with an Ex Max of 348-nm and an acceptor dye with an Em Max at 496-nm. BD Horizon BUV496 can be excited by the ultraviolet laser (355 nm) and detected with a 515/30 nm filter with a 450LP. Due to the excitation of the acceptor dye by other laser lines, there may be significant spillover into the channel detecting BD Horizon V500 or BV510 (eg, 525/40-nm filter). However, the spillover can be corrected through compensation as with any other dye combination.