Functional analysis of novel molecules differentially expressed during dendritic cell maturation

Research project P 13794 Novel molecules expressed by dendritic cells Christine HEUFLER TIEFENTHALER 28.06.1999 The Immune system is composed of cells and molecules which function together to protect the individuum against foreign substances and microbes. The dendritic cell (DC) is one of these cells and is specialized in priming cellular immune responses. The activation of naive resting T-cells is crucial for primary immune responses and can be performed only by DCs. In addition DCs have recently been shown to be involved in B-cell growth and immunoglobulin secretion as well as in maintaining self tolerance. Increasing attention is being posed on the antiviral status of DCs which has been described: DCs can control the replication of many viruses to a level sufficient for antigen presentation but not for virally induced cell death. The molecular mechanisms of many of the specialized features of DCs are still only partially known. In our previous projects (SFB 002/07 and P11522-Med) we have identified and/or characterized several molecules differentially expressed by DCs in different functional stages: 1. the cytokine IL-12, which has been shown by us and others to be crucial for immunoregulation, 2. a STAT factor activation pattern which in response to GM-CSF is unique in DC, 3. a novel intracellular protein termed M1204 which is upregulated during the maturation of DCs. From its ability to synthesize diadenylate it might accelerate RNAseL activation and therefore possibly contributes to the antiviral status of DCs. 4. another cytosolic protein, HE, which interacts with cytohesin and may therefore be involved in the regulation of expression of adhesion molecules and 5. H50, a membran bound surface molecule with homology to a group of related proteins including the CD80 molecule, which is a necessary costimulatory signal in T-cell activation. The aim of this study is to further characterize these molecules especially in terms of their putative functions. Understanding the function of these molecules may provide new approaches toward modulation of the immune status as needed for many different clinical situations.

In the course of the project we identified a number of molecules induced during the maturation process of dendritic cells and provide evidence for their impact on the function of dendritic cells. Detailled understanding of dendritic cell function will eventually allow to better manipulate these cells for immunotherapy of cancer. Dendritic cells are the main antigen presenting cells for the activation of naive T-cells to mount an antigen specific immune response. Between the time for antigen uptake in the periphery of the body and the time for T-cell activation in the secondary lymphoid organs dendritic cells undergo a maturation process which allows to define two stages of dendritic cell function. The maturation process is characterized by changes in mophology and anatomical location, the expression of specific markers and the acquisition of novel functions. This project was intended to collect molecular features underlying this maturation process. We concentrated on the molecular and/or functional characterization of two molecules induced during the maturation process of dendritic cells: a novel molecule termed CYTIP, which regulates cellular adhesion and the adenosine receptors, which upon engagement slow the migration of dendritic cells. For the protein termed CYTIP we could outline a novel mechanism for the interruption of signalling events leading to cell adhesion. During the antigen specific activation of T-cells, dendritic cells need to screen a high number of T-cells to find the few (about 1 in 100.000 to 1 million) which are specific for the presented antigen. This screening process is thought to involve short term cell adhesion, which is further strengthened if the specificity is right, or abolished if it is not. We postulate that our molecule which rapidly abolishes cell adhesion might help to control this process. The second family of molecules investigated are receptors for adenosine which caught our attention because two of the four known receptors are regulated during dendritic cell maturation. Adenosine, the ligand of this receptor family, is known to modulate physiological responses in all mammalian tissues. Inflammation, among others, stimulates local adenosine production and dendritic cells are known to respond to inflammatory stimuli by maturation. We looked for a possible link of these inflammation-induced events and found that engagement of adenosine receptors on dendritic cells lead to a delay in their migration and consequently in their anatomical relocalisation. We postulate that this might help to control antigen specific immune responses by delaying the encounter of antigen specific T-cells in the secondary lymphoid organs.