Phenotype and tissue distribution of CD28H+ immune cell subsets.

CD28H is a newly discovered co-receptor of the human B7 family. CD28H interacts with its ligand B7-H5 and regulates T cell response. Here we showed that CD28H was not expressed on granulocytes, monocytes, myeloid dendritic cells (MDCs), and B cells, but constitutively expressed with moderate levels on memory T cells and with high levels on naïve T cells, innate lymphoid cells (ILCs), natural killer (NK) cells, and plasmacytoid dendritic cells (PDCs) in human peripheral blood. Similar CD28H+ cell profile existed in secondary lymphoid organs and pathological tissues including multiple types of cancers. Further analysis demonstrated that CD28H+ naïve and CD28H+ memory T cells were characterized with increased naïve feature and less effector functional phenotype, respectively. High levels of constitutive CD28H expression on naïve T cells and innate immune cells suggest a potential role of CD28H in innate and adaptive immunity.