UVA1 irradiation induces deoxyribonuclease dependent apoptosis in cutaneous T-cell lymphoma in vivo

Cutaneous T-cell lymphoma (CTCL) is a malignancy of mature T-cells, predomi nantly of the helper phenotype, that primarily invade the skin. Different p hoto-and chemotherapeutic treatments are known to be beneficial in early-st age CTCL, This observation has initiated prospective investigations into th e efficacy of phototherapeutic regimens. The purpose of our study was to in vestigate the ability of medium-dose UVA1 phototherapy (60 J/cm(2)) to indu ce apoptosis (programmed cell death) in skin infiltrating T-cells of CTCL i n vivo. We describe the results of three different staining methods for for malin-fixed, paraffin-embedded tissue sections. The in situ end-labeling (I SEL) procedure, nuclear staining using the DNA-binding fluorochrome Hoechst 33342, and immunohistochemistry using polyclonal antibodies against recomb inant mouse deoxyribonuclease I (DNase I) demonstrated that UVA1 irradiatio n was able to induce marked apoptosis in CTCL. Thereby, ISEL and Hoechst st aining clearly revealed DNA-condensation and nuclear fragmentation, accompa nied by the formation of typical "apoptotic bodies". The accumulation of DN ase I immunoreactivity in the cytoplasm of lymphocytes in UVA1 irradiated s kin indicated that DNase I or DNase I-related endonucleases may have acted as apoptotic endonuclease(s) which were synthesized after UVA1 irradiation prior to their apoptotic elimination.