This gene encodes a protein that regulates thymic epithelial cell proliferation and thymus size. It has been identified as a ligand for the class I human leukocyte antigen (HLA-I) in thymus. Studies of the orthologous mouse protein suggest that it may also play a role in spermatid differentiation, as well as in neuronal morphogenesis and synaptic plasticity. Polymorphisms in this gene are associated with susceptibility for multiple sclerosis (MS). Alternative splicing results in multiple transcript variants. [provided by RefSeq, Dec 2015].