Differential sensitivity of freshly isolated and cultured murine Langerhans cells to ultraviolet B radiation and chemical fixation.

Previous studies have demonstrated that low doses of ultraviolet B (UVB) radiation (100 J/m2) abrogate the accessory function of freshly isolated murine epidermal Langerhans cells (fLC) and cause a parallel decrease in the ability of LC to express increased amounts of ICAM-1 (CD54) in vitro. We have subsequently observed that the accessory cell function of cultured LC (cLC), as assessed by their ability to support anti-CD3 monoclonal antibody (mAb)-induced T cell mitogenesis, was not inhibited by levels of UVB exposure (100 J/m2) that completely inhibited the function of fLC, although exposure of cLC to UVB radiation (100 J/m2) resulted in a decrease in the level of ICAM-1 expression on most cLC and a concomitant decrease in cLC survival during a subsequent 24-h incubation. Time course studies revealed that T cells stimulated with anti-CD3 mAb in the presence of cLC became committed to proliferate 4-8 h after culture initiation, while 24-30 h of co-culture was required for irreversible T cell activation when fLC were utilized as accessory cells. In addition, paraformaldehyde (PFA)-fixed (non-viable) cLC supported anti-CD3 mAb-induced T cell proliferation, whereas PFA-fixed fLC were ineffective. We propose that cLC are functionally resistant to low doses of UVB radiation and chemical fixation because cLC express sufficient levels of the adhesion or co-stimulatory molecules [including ICAM-1 and Mac-1 (CD11b/CD18)] required to induce T cell activation. Conversely, fLC are sensitive to the effects of UVB radiation and chemical fixation because these physicochemical agents prevent acquisition of critically important surface molecules in culture.