Lysosomal thiol reductase that can reduce protein disulfide bonds. May facilitate the complete unfolding of proteins destined for lysosomal degradation. Plays an important role in antigen processing. Dimer; disulfide-linked. Highly expressed in spleen and kidney. Also detected at lower levels in liver, heart, brain, intestine and gill. Strongly up-regulated in spleen and kidney in response to bacterial lipopolysaccharide (LPS). Belongs to the GILT family.