EFFECT OF STORAGE AND ULTRAVIOLET-B IRRADIATION ON CD14-BEARING ANTIGEN-PRESENTING CELLS (MONOCYTES) IN PLATELET CONCENTRATES

Background: Ultraviolet B (UVB) irradiation of platelet concentrate (P Cs) reduces platelet alloimmunization, but the mechanism of the effect is unclear. Evidence suggests that UVB may downregulate the expressio n of surface adhesion molecules on passenger antigen-presenting cells in PCs. Study Design and Methods: The effect of blood bank storage, pl atelet preparation from whole blood, and UVB irradiation on the quanti tative expression of intercellular adhesion molecule-1 (ICAM-1, or CD5 4), HLA-DR, CD45, and CD11c on CD14-positive antigen-presenting cells (monocytes) was studied by using two-color flow cytometry. Results: Bl ood bank storage for 4 days resulted in upregulation of ICAM-1 and HLA -DR and downregulation of CD14 but left the expression of CD11c and CD 45 unchanged Preparation of PCs from fresh whole blood was associated with a rapid increase in CD11c without upregulation of ICAM-1 and HLA- DR. UVB irradiation before storage inhibited the upregulation of ICAM- 1 and HLA-DR, resulted in accelerated downregulation of CD14, and was associated with increased loss of monocytes. Agitation of the PC bag d uring irradiation was of critical importance, since omission of agitat ion resulted in largely uninhibited upregulation of ICAM-1 but was sti ll associated with significantly higher cell loss than that seen in un irradiated controls. Conclusion: UVB exposure nonspecifically affects monocytes in PCs, resulting in downregulation of surface molecules tha t are important for antigen presentation, as well as in significant ce ll loss.