However, both proteins have similar biological functions and show 70% identity in amino acid sequence.

On its N terminus it possesses catalytic domain, which shows the highest level of conservation between human and mouse proteins.

[10] PTPN22 possess the ability to dephosphorylate proteins included in proximal events of the TCR signaling and serves as an important negative regulator of a T cell activation.

Increased responsiveness can also break the tolerance against low affinity self-antigens and is well visible, when PTPN22-deficient T cells get into a lymphopenic environment.

Treatment of PTPN22-deficient mice with an anti-GITR-L blocking antibody suppresses the expansion of Treg cells.

Actually there are some articles suggesting that PTPN22-deficient Treg cells possess an enhanced suppressive function or have a bigger ability to obtain an effector phenotype.

[23] The role of the PTPN22 in the regulation of LFA-1-mediated adhesion and motility is also supported by the observation of increased LFA-1 expression in PTPN22-/- Treg cells.

[13] The C-terminal part of the PTPN22 bare proline-rich motifs providing binding sites for putative interaction partners.

[16][24] It was also proposed that the interaction of PTPN22 and CSK regulate a localization of the PTPN22 and a dissociation of this complex enables translocation of the PTPN22 to lipid rafts of a plasma membrane, where it can inhibit a TCR signaling.

PTPN22 is phosphorylated on the serine in the position 751 by the protein PKC (most probably isoform PKCα) after activation of a T cell.

Phosphorylared PTPN22 interacts better with the CSK which hold PTPN22 away from a plasma membrane, where it can dephosphorylate proteins of a TCR signaling pathway.

PTPN22 with the mutated serine 751 has shorter half-life, enhanced recruitment to plasma membrane and reduced interaction with CSK.

[17] Another abnormality of PTPN22-deficient mice is a spontaneous formation of large germinal centers in spleens and peyer's patches.

Despite those effects of the PTPN22 deficiency on a T cell compartment and an antibody production, PTPN22-deficient mice do not show signs of any autoimmune disease.

The article reporting the existence of this variant also discovered that it is more frequent in Diabetes mellitus type 1 patients.

On the other hand, this allele is not linked to autoimmune diseases like multiple sclerosis, Ulcerative colitis, pephigus vulgaris and others.

[6][5] Overview of all the structural information available in the PDB for UniProt: Q9Y2R2 (Tyrosine-protein phosphatase non-receptor type 22) at the PDBe-KB.