The occurrence of mucosa-associated lymphoid tissue (MALT) is not a ubiquitous finding in the nasolacrimal ducts (although it is a feature commonly found in symptomatically normal nasolacrimal ducts)  and is acquired in response to antigenic stimulation. Loss of tear-duct-associated lymphoid tissue (TALT) seems to be associated with the scarring of symptomatic dacryostenosis, suggesting that the presence per se of TALT does not lead to scarring . Whether special types of bacteria, viruses, allergic reactions, or other factors, such as some type of immune deviation (see below), are responsible for the development of TALT in humans is not clear at present; however, the occurrence of TALT may favor the rise of primary low-grade B-cell lymphoma of the MALT
type, as has been shown by Kheterpal et al. , White et al. , and Tucker et al. .
Within the scope of this chapter it is impossible to review special immunological features of the eye; however, it should be mentioned that the anterior eye chamber (comparable to brain, placenta, testicle) has a special immunological state of reduced activation of the specific and non-specific immune system. This condition of local immune suppression, termed the immune privilege, is expressed in delayed or totally suppressed rejection of allogenic transplantations in these organs. This is illustrated in the survival of corneal and lens transplants in the anterior eye chamber and is called immune tolerance. It is known that such tolerance is transferable by injection into a second animal of splenocytes from an animal that was primed by inoculation of an antigen, demonstrating that antigens from the anterior eye chamber receive a signal that produces immune deviation and that regulatory T-cells have developed.
Recent analysis indicates that defective stimulation of TALT (Fig. 2.9) could result in abnormal immune deviation at the ocular surface leading to an autoim-munological response that causes dry-eye pathology. For more and detailed explanation see work by Paulsen et al. .
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