Effect of UV light on tumor cell sensitivity to NK and NC cell-mediated lysis

The effect of UV light irradiation on the immunobiological properties of murine tumor cells was studied. In vitro irradiation of MCA 102 and MCA 105 fibrosarcomas with a short-wavelength UVC light rendered them highly immunogenic and sensitive to natural cell-mediated cytotoxicity (NCMC). Analysis of the effector cells involved in NCMC revealed that UV irradiation stably increased tumor cell sensitivity to both NK and NC cell lysis. Studies of the mechanisms responsible for increased sensitivity to NK cells indicate that UV treatment did not affect tumor-cell recognition by NK cells but increased their susceptibility to NK-derived lytic granules. Augmentation of UV-treated tumor cell sensitivity to NC cell-mediated lysis was found to be due to their increase in sensitivity to the effector-cell-released TNF. In parallel, UV-treated cells showed high sensitivity to human recombinant TNF whereas untreated parental cells were resistant to rTNF. UV irradiation did not affect rTNF binding, internalization and degradation but increased tumor cell vulnerability to TNF-induced DNA fragmentation. Thus, UV light appears as a potent modulator of tumor cell sensitivity to T cell- and natural cell-mediated immunity.