The involvement of T lymphocyte subsets in the immunopathology of herpetic stromal keratitis (HSK)

The term immunopathology (IP) is used to describe pathological conditions which are caused by different effector arms of the immune system such as cytotoxic T cells, hypersensitivity responses, and antibodies (Sell, 1987).The end product of immunopathological reactions are functional impairments and morphological degenerations in the affected tissues. The characteristic feature of immunopathological reactions is an unwanted and uncontrolled immune response. Implicit in this feature is that experimental manipulations on the functions of the immune elements result in dramatic changes in the clinical symptoms of immunopathological conditions. Thus, immunosuppressive, or immunopotentiating regimens have been the method of choice to study immunopathological models. As more sophisticated means of manipulating immune effector cells have become available, our detailed understanding of the mechanisms of IP have increased considerably (Kumar et.al., 1989). In classical immunology textbooks, immunopathological reactions are classified according to:

-the mechanisms of the pathology e.g. allergic reactions, and immune complex reactions,

-the source of the immune factors mediating the IP e.g. endogeneous immune factor mediated (autoimmune type reactions), and exogenous immune factor mediated (graft versus host reactions),

-the source of the antigen to which immunopathological responses are directed e.g. exogenous antigens (tuberculin reactions), and endogenous antigens (demyelinating diseases). In the first half of this review, the IP of viral infections, and the role of individual T lymphocyte subsets in the development of these conditions will be outlined. The discussion will be limited to selected viral and parasitic models where the pathology is mediated by T lymphocytes and an adoptive transfer approach has been established for IP. At times, the length of this section seems exhaustive, however, many of the conclusions drawn from these models are crucial in understanding and evaluating the current status and future directions of investigations on herpetic stromal keratitis (HSK). The second half of the review will summarize immunopathological conditions observed in herpes simplex virus (HSV) infections with an emphasis on herpetic stromal keratitis (HSK).