Additional isoforms seem to exist. Experimental confirmation may be lacking for some isoforms. Expressed ubiquitously at low levels. High levels of expression are confined to hematopoietic tissues including peripheral blood leukocytes, thymus and spleen. Expressed from early embryogenesis through to adulthood. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the tetraspanin (TM4SF) family.