Normally when we hear the word immunity, we think of defense against infections, graft rejection, inflammation, etc. But, what if this defense may cause more damage than the infection itself ? In this case, the immune system shows a certain privilege through acting smarter where it deviates its mechanisms in a way to down-regulate its own damaging mechanisms. This whole process is known as Anterior Chamber-Associated Immune Deviation (ACAID).
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ACAID is endogenous to specific sites such as the anterior chamber of the eye and the brain. The process is considered as saving in cases of ocular infections where the visual axis is easily deflected by inflammation leading to blindness. Also ACAID is considered beneficial in case of allografting as it downregulates the immune processes responsible for allograft rejection. The process was discovered by Medwar in 1940, when he first noticed that surprisingly certain tumors proliferate more rapidly in the anterior chamber of the eye than anywhere else. Medwar’s further studies demonstrated the role of the process in transplantation immunology.
As an example of ACAID, upon antigenic inoculation of anterior chamber of the eye, the immune deviation presents itself as follows: Instead of Natural Killer T-cells perform certain functions attributed to T-Helper & T-Cytotoxic cells, the antigen injected into the eye APCs (Antigen Presenting Cells) that carry antigen to the spleen. These APCs activate NKT cells which in turn produce certain cytokines as TGF-ß that induce the generation of CD8+Tr cells which by production of cytokines such as TGF-ß and IL-10, can downregulate subsequent Th1-mediated DTH reactions against the same antigen.
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Thus, regarding the beneficial effects that can be drawn from ACAID, current research is being conducted for inducing ACAID to avoid graft and transplant rejection. ACAID can be induced by animal injection with non-ocular APCs, e.g., peritoneal exudate cells (PECs) that have been precultured with TGF-ß and antigen in vitro. Such procedure is believed to be a step forward toward the success of transplantation.