Short Description: The protein encoded by this gene was identified by a two-hybrid screen using CD4 as the bait. It binds to the hydrophobic C-terminal amino acids of CD4 which are involved in repression of T cell activation. The interaction with CD4 is mediated by the noncatalytic alpha/beta hydrolase fold domain of this protein. It is thus proposed that this gene product modulates the stimulatory activity of CD4. At least three different transcript variants encoding two different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]. More information related to gene SPG21.