Different Pathways Of Allorecognation Direct, Indirect,...

There are three pathways of allorecognation: direct, indirect, and linked pathways. The difference of direct and indirect pathways is the work of dendritic cells in presenting the donor peptides as foreign antigens. In direct pathway, the dendritic cells migrate directly from the graft into the recipient’s lymph nodes and present the antigen to their own MHC to T cell receptor (TCR). This will excite an anti-donor T-cell allorecognition response and lead to rejection. Both CD4+ and CD8+ are capable for this. Conversely, in indirect pathway, the dendritic cells migrate to the graft, take and process some proteins from the recipient cells and present it on MCH to T cells in lymph nodes. While, linked allorecognation is by using direct transfer of cell membrane from donor dendritic cells to recipient dendritic cells.3,4 (Figure 2) There are six MHC class I isotypes: HLA-A, HLA-B, HLA-C, HLA-E, HLA-F, and HLA-G while for MHC class II : HLA-DM, HLA-DO, HLA-DP, HLA-DQ, and HLA-DR. As the fact that every single person has different type of HLA and may be provided as a foreign antigen in other individual, HLA take significant role on the rejection response in organ transplantation.1,2 Chronic Rejection in Organ Transplantation Chronic rejection is characterized as a slow process of a tissue replacement in allograft into fibrous scar tissue as fibroproliferative changes by some immune (antigen-dependet) and non immune factors (antigen-independent).4 Chronic Rejection may takes