Presence and possible significance of immunohistochemically demonstrable metallothionein expression in pterygium versus pinguecula and normal conjunctiva.

Abstract

To investigate metallothionein (MT) expression in pterygium, pinguecula and normal conjunctiva and define its possible significance in this area of the eye. In order to further elucidate the mechanism of MT expression we correlated it with lymphocyte subpopulations (T4, T8), macrophages (CD68), Langerhans' cells (S100) and the proliferation-associated indices (PCNA, Ki67). Eighty-five surgically excised pterygia, 15 pingueculae and 20 normal conjunctivae were immunohistochemically studied by the avidin-biotin (ABC) method. A monoclonal antibody (E9) against a conserved epitope of I and II isoforms of MT was used on formalin-fixed, paraffin-embedded tissues. Statistical analysis was performed using the SPSS statistical package. Epithelial MT expression was detected in all 120 cases examined and in most of them both nuclear and cytoplasmic immunoreactivity was present. Nevertheless no statistically significant difference of MT expression was found between the three types of tissue. A statistically significant positive correlation between MT expression and lymphocyte subsets, macrophages and Langerhans' cells was found in pterygium. On the contrary, we did not find any statistical correlation in pinguecula and normal conjunctiva. In all three types of tissues MT expression was also positively correlated with the proliferation-associated indices. The data suggest that there is immunohistochemically demonstrable MT expression in the epithelium of pterygium, but also of normal conjunctiva and pinguecula. MT may serve a photoprotective role in this region. In pterygium in particular, the biochemical pathway of MT synthesis seems interestingly to cross the pathways of cell proliferation, inflammation and immune activation.