Expressed at the plasma membrane in epithelia involved in fluid transport, including type I alveolar epithelial cells, choroid plexus, and ciliary epithelium, the specific function of this protein has not been determined but it has been proposed as a marker of lung injury. T1A-2 has a broad tissue distribution with strong expression in lung, placenta and skeletal muscle. The physiological function of this protein may be related to its mucin-type character. The homologous protein in other species has been described as a differentiation antigen and influenza-virus receptor.