Direct Ni2+ antigen formation on cultured human dendritic cells

The possible direct antigen formation of Ni2+ on antigen-presenting cells ( APCs) was studied with cultured human dendritic cells (DCs) obtained from 1 0 subjects contact allergic to Ni2+ and six non-allergic control individual s. All contact allergic subjects showed a significantly increased periphera l blood mononuclear cell(PBMC) response in vitro to Ni2+. DCs were expanded from the plastic-adherent cell fraction of PBMCs by culturing with granulo cyte macrophage colony-stimulating Factor (GM-CSF) and interleukin-4 (IL-4) for 7 days to obtain immature DCs, and with the addition of monocyte-condi tioned medium for another 4 days, for DC maturation. The DCs were pulsed fo r 20 min with Ni2+ (50 mu M) in protein-free Hank's balanced salt solution (HBSS) and added to freshly prepared autologous responder PBMCs. With five allergic subjects, immature DCs pulsed with Ni2+ demonstrated a significant capacity to activate Ni2+-reactive lymphocytes. With the remaining five pa tients and the six controls no difference in lymphocyte proliferation was o bserved between Ni2+-pulsed and non-pulsed immature DCs. In contrast, with mature Ni2+-pulsed DCs from both 'positive responder' (n = 4) and 'non-resp onder' (n = 4) patients, there was a significantly stimulated PBMC prolifer ation, whereas with the controls (n = 4) still no activation was observed. Our results indicate that direct formation of the antigenic determinant of Ni2+ on APCs is possible and that Ni2+ uptake and processing mechanisms may not play a major role. Differences in the ease of activation of Ni2+ -reac tive lymphocytes are discussed in terms of a possible heterogeneity in the availability of Ni2+ -reactive groups presented on endogenous peptides boun d in the antigen binding groove of human leucocyte antigen (HLA) class-II m olecules.