[Isoform 2]: Behaves as a cytokine, promoting IL17A secretion by CD4+ T-cells, and differentiation and activation of IL17 producing helper T-cells (TH17). [Isoform 1]: Inhibitory immune receptor involved in the regulation of phagocytes. This is the function of ENSG00000189068 (VSTM1, V-set and transmembrane domain containing 1).