PD-L2 binds to its receptor PD-1 with dissociation constant Kd of 11.3 nM.[17] Binding to PD-1 can activate pathways inhibiting TCR/BCR-mediated immune cell activation[12] (for a more detailed discussion see PD-1 signaling). PD-L2 plays an important role in immune tolerance and autoimmunity.[18] Both PD-L1 and PD-L2 can inhibit T cell proliferation and inflammatory cytokine production.[17] Blocking PD-L2 has been shown to exacerbate experimental autoimmune encephalomyelitis.[18] Unlike PD-L1, PD-L2 has been shown activate the immune system. PD-L2 triggers IL-12 production in murine dendritic cells leading to T cell activation.[17] Others have shown that treatment with PD-L2 Ig led to T helper cell proliferation.[18]
The direct role of PD-L2 in cancer progression and immune-tumor microenvironment regulation is not as well studied as the role of PD-L1.[16] In mouse cell cultures, PD-L2 expression on tumor cells suppressed cytotoxic T cell-mediated immune responses.[20]
Indirectly, PD-L2 may have utility as a biomarker or prognostic indicator. PD-L2 expression has been shown to predict response to PD-1 blockade with pembrolizumab independently of PD-L1 expression.[16] However, PD-L2 does not putatively predict outcome in cancer, with some studies suggesting it predicts negative prognoses[21][22][23] and other studies suggesting it predicts positive prognoses.[24]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^ abcLatchman Y, Wood CR, Chernova T, Chaudhary D, Borde M, Chernova I, et al. (March 2001). "PD-L2 is a second ligand for PD-1 and inhibits T cell activation". Nature Immunology. 2 (3): 261–8. doi:10.1038/85330. PMID11224527. S2CID27659586.
^ abChen L (May 2004). "Co-inhibitory molecules of the B7-CD28 family in the control of T-cell immunity". Nature Reviews. Immunology. 4 (5): 336–47. doi:10.1038/nri1349. PMID15122199. S2CID33548210.
^ abcdSharpe AH, Wherry EJ, Ahmed R, Freeman GJ (March 2007). "The function of programmed cell death 1 and its ligands in regulating autoimmunity and infection". Nature Immunology. 8 (3): 239–45. doi:10.1038/ni1443. PMID17304234. S2CID8749576.
Youngnak P, Kozono Y, Kozono H, Iwai H, Otsuki N, Jin H, et al. (August 2003). "Differential binding properties of B7-H1 and B7-DC to programmed death-1". Biochemical and Biophysical Research Communications. 307 (3): 672–7. doi:10.1016/S0006-291X(03)01257-9. PMID12893276.
Aramaki O, Shirasugi N, Takayama T, Shimazu M, Kitajima M, Ikeda Y, et al. (January 2004). "Programmed death-1-programmed death-L1 interaction is essential for induction of regulatory cells by intratracheal delivery of alloantigen". Transplantation. 77 (1): 6–12. doi:10.1097/01.TP.0000108637.65091.4B. PMID14724428. S2CID25360886.
Mataki N, Kikuchi K, Kawai T, Higashiyama M, Okada Y, Kurihara C, et al. (February 2007). "Expression of PD-1, PD-L1, and PD-L2 in the liver in autoimmune liver diseases". The American Journal of Gastroenterology. 102 (2): 302–12. doi:10.1111/j.1572-0241.2006.00948.x. PMID17311651. S2CID8083797.
Wang SC, Lin CH, Ou TT, Wu CC, Tsai WC, Hu CJ, et al. (April 2007). "Ligands for programmed cell death 1 gene in patients with systemic lupus erythematosus". The Journal of Rheumatology. 34 (4): 721–5. doi:10.1093/rheumatology/34.8.721. PMID17343323.