Ultraviolet irradiation of canine dendritic cells prevents mitogen-induced cluster formation and lymphocyte...

The objectives of this study were to characterize canine peripheral blood dendritic cells (DC), to compare their functional role in lectin (Con-A) induced and oxidative (NaIO4-induced) mitogenesis, and to investigate the effect of ultraviolet (UV) irradiation on DC function. We used, sequentially, Ficoll-Hypaque fractionation, discontinuous percoll gradients, rosette, sedimentation with human red blood cells, adherence to plastic and cytofluorometric sorting after labeling with an anti-Ia monoclonal antibody (7.2) to obtain cells of low buoyant density that were rosette-negative, plastic-non-adherent, Ia-positive, nonspecific-esterase-negative, and nonphagocytic. By transmission and scanning electron microscopy these cells had large irregular nuclei, numerous spherical mitochondria, elongated cytoplasmatic processes, and lacked phagosomes. These features clearly separate these cells from canine monocytes and characterize them as DC. These cells were capable of reconstituting the proliferative responses of accessory-cell-depleted autologous lymphocytes to both Con-A and NaIO4. The responses to both mitogens showed a similar time course: an initial cluster formation of lymphocytes with DC was followed by lymphocyte blastogenesis (48-72 hr) and proliferation (72-96 hr). UV irradiation of DC before culture completely abrogated accessory activity for the response to both Con-A and NaIO4, and neither cluster formation nor blast transformation or proliferation occurred. These data provide evidence that a UV-sensitive step of direct interaction of lymphocytes and DC is involved in the mechanism of T cell activation and proliferation.