Effects of bacterial adjuvants on human antigen presenting cells

In this thesis, the hypothesis addressed is that different bacterial components may behave as adjuvants by modulating DC function through changes in co-stimulatory molecule expression and production of soluble mediators in a way that would differentially stimulate T-cell proliferation. The dendritic cells used in this study are monocyte-derived dendritic cells (mo-DC). Synthetic oligodeoxynucleotiedes (ODN) containing CpG motifs and outer membranes of Neisseria meningitidis were investigated as bacterial-derived adjuvants. Immunomodulatory effects of bacterial DNA are attributed to the presence of CpG-motifs. Similarly, ODN containing CpG-motifs are reported to possess stimulatory activity on a variety of immune cells. One aim of this study was to examine the effects of CpG-ODN on CD80, CD86, CD40 and HLA-DR expression and cytokine production by monocytes and mo-DCs. The results revealed striking differences between the effects of CpG ODN on monocytes and mo-DCs. Monocytes treated with CpG markedly up-regulated CD86 expression as well as induced production of IL-1b, IL-6, IL-10 and IL-12p40. Similar changes in phenotype were observed in CpG-treated monocytes obtained from non-atopic and atopic individuals. By contrast, no-DCs treated with CpG ODN failed to show any changes in expression of co-stimulatory molecules and HLA-DR, production of cytokines and did not affect mo-DC driven allogeneic T-cell proliferation. These findings indicate that the in vitro differentiation of monocytes to mo-DC alters their responsiveness to CpG DNA and correlates with the loss of Toll-like receptor (TLR) 9during this differentiation. Expression of TLR9 was observed on human epidermal Langerhans' cells (LC) and not on CD34+-derived DCs suggesting that LC are CpG responsive cells. Differential expression of TLR2, TLR4 and TLR9 on monocytes and distinct DC subsets suggests that activation by bacterial components is facilitated following recognition through specific receptors.