Proliferative activity of epidermal and dermal T lymphocytes in mycosis fungoides.

Background: Mycosis fungoides (MF) is histologically characterized by an accumulation of T lymphocytes (T cells) in both epidermis and dermis. However, the mechanism of the formation of Pautrier's microabscess or the maintenance of the epidermal T cells has not yet been clarified.

Objective: The rate of proliferation of these T cells was investigated.

Methods: The formalin-fixed, paraffin-embedded sections from 9 cases of patch/plaque stage MF were immunostained with proliferating cell nuclear antigen (PCNA).

Results: The PCNA-positive T cell nuclei were found both in the epidermis (including Pautrier's microabscesses) and dermis in all the specimens. The mean PCNA indices of the T cells were 20.2 +/- 10.6% (mean +/- SD) within the epidermis and 16.8 +/- 6.5% in the dermis, which was not statistically significantly different (p > 0.05). The ratio of the PCNA index between the epidermis and dermis was 1.3 +/- 0.6, which was not apparently correlated with the duration of the disease (8.4 +/- 5.1 years).

Conclusion: These findings suggested that in situ proliferation might contribute to the epidermal T cell population resulting in the formation of Pautrier's microabscesses and an increase in dermal T cell volume during the course of the disease.