IFI3 belongs to the GILT family. This family includes the two characterised human gamma-interferon-inducible lysosomal thiol reductase (GILT) sequences: P13284 and Q9UL8. It also contains several other eukaryotic putative proteins with similarity to GILT. The aligned region contains three conserved cysteine residues. In addition, the two GILT sequences possess a C-X(2)-C motif that is shared by some of the other sequences in the family. This motif is thought to be associated with disulphide bond reduction. IFI3 is a lysosomal thiol reductase that can reduce protein disulfide bonds. It facilitates the generation of MHC class II-restricted epitodes from disulfide bond-containing antigen by the endocytic reduction of disulfide bonds. It also facilitates MHC class I-restricted recognition of exogenous antigens containing disulfide bonds by CD8+ T-cells or crosspresentation. IFI3 may facilitate the complete unfolding of proteins destined for lysosomal degradation and plays an important role in antigen processing.