Photodynamic alteration of the surface receptor expression pattern of murine splenic dendritic cells

The photosensitizer benzoporphyrin-derivative monoacid ring A (BPD-MA, vert eporfin), in combination with visible light irradiation, a clinical procedu re termed photodynamic therapy (PDT), has immunomodulatory activity in vari ous mouse models. We studied the impact of BPD-MA and light upon DBA/2 mous e splenic dendritic cells (DC), a potent antigen-presenting cell (APC) type . DC treated with nanomolar amounts of BPD-MA and 690 nm wavelength light h ad a reduced capacity to stimulate the proliferation of alloreactive T cell s. Treatment with BPD-MB and light reduced DC levels of major histocompatib ility (MHC) Class I and II antigens, intercellular adhesion molecule-1 (ICA M-1, CD4), the costimulatory B7-1 (CD80) and B7-2 (CD86) molecules, leucocy te common antigen CD45, the apoptosis-regulating Fas (CD95) receptor and th e integrin CD11c. In contrast, DC expression of leucocyte function-associat ed-1 (LFA-1, CD11a), Mac-1 (CD11b), integrin beta(2) chain (CD18) and the D EC-205 receptor increased, while CD40 levels were relatively unchanged 24 h after the treatment. MHC Class I and ICAM-1 levels decreased to 40% Of con trol levels within 2 h following the photodynamic treatment. In the absence of light, BPD-MA did not affect DC receptor levels. Changes in DC receptor levels produced by BPD-MA and red light were similar to those produced by ultraviolet B light irradiation. The photodynamic treatment of activated sp lenic B cells, a sepal-ate APC class, had little effect upon receptor expre ssion, except that MHC Class II levels were moderately decreased 24 h later . Changes in DC receptor expression may contribute to the immunomodulatory action of PDT.