Semi-mature IL-12 secreting dendritic cells present exogenous antigen to trigger cytolytic immune responses.

Dendritic cells (DC) are candidates for antigen-presenting cells that present exogenous antigen on MHC class I molecules to cytotoxic T lymphocytes (CTL), a process referred to as cross-priming. We triggered interleukin (IL)-12 release from DC, which was limited to the first day after maturation induction, by a combination of lipopolysaccharide (LPS) and interferon (IFN)-gamma. To stimulate T lymphocytes, we used soluble protein derived from lysis of Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCL) or ovalbumin loaded onto DC. Co-culture was initiated 2-6 or 48 h after maturation corresponding to "semi-mature" actively IL-12-secreting type 1 DC (sm-DC1) or a "fully mature" DC1 that had lost the ability to release IL-12 (fm-DC1), respectively. IL-12-secreting sm-DC1 but not fm-DC1 efficiently triggered cytolytic activity in autologous T lymphocytes. The combination of IL-1beta, IL-6, TNF-alpha, and prostaglandin E2 generated type 2 DC that did not secrete IL-12 (DC2) and could not prime T-cell cytolytic activity. However, supplementation of cultures using DC2 with IL-12 resulted in CTL activity while the presence of anti-IL-12 monoclonal antibodies in cultures using IL-12 secreting sm-DC1 suppressed CTL activity. Thus, actively IL-12-secreting sm-DC1 are necessary and sufficient for the antigen-specific expansion of CTL in response to exogenously provided soluble antigen.

Normal monocyte-derived dendritic cell function in patients with Langerhans-cell-histiocytosis.

BACKGROUND: Langerhans cell histiocytosis (LCH) is a histiocytic disease, characterized by the lesional accumulation of dendritic Langerhans cells together with T cells and eosinophils. The cause of this disease is unknown. Langerhans cells are bone marrow-derived dendritic cells (DCs), which can develop from CD34(+) hematopoietic progenitor cells as well as from monocytes. PROCEDURE: To test whether LCH patients have a general functional defect present in cells of their DC lineage, we generated immature DCs by culturing monocytes from nine patients with single- or multisystem LCH with GM-CSF and IL-4, and analyzed their phenotype and function before and after an in vitro maturation stimulus. Immature DCs were analyzed for their phenotype and cytokine production, DCs matured in response to TNF-alpha plus PGE(2) were analyzed for their phenotype, their stimulatory capacity in MLR, cell aggregation, and activation-induced apoptosis. RESULTS: In summary, no difference was found between both immature as well as mature DCs generated from patients and controls regarding the expression of CD1a, CD80, CD86, MHC class I, and MCH class II antigens. Similarly, no difference was found regarding IL-10, -12, and TNF-alpha production, as well as regarding cell aggregation and apoptosis in response to external stimuli. CONCLUSIONS: The absence of gross functional abnormalities in DCs generated from monocytes from patients with LCH makes the existence of a severe functional defect affecting all cells of the DC lineage in these patients unlikely.