Lipid rafts, pseudotyping, and virus-like particles: relevance of a novel, configurable, and modular antigen-presenting platform.

Antigen presentation by professional antigen-presenting cells (APC) is the first step towards the initiation of an adaptive immune response carried out by naïve T lymphocytes. For this purpose, antigens are presented in the form of peptide/major histocompatibility complexes (pMHC) on APC to the antigen receptor of T cells. For sustained T cell activation to occur, numerous additional molecules specifically expressed on the surface of APC have to synergize with pMHC to stimulate a given T lymphocyte. Moreover, soluble factors such as cytokines critically contribute to the specific milieu during T cell activation. APC 'talk' to T cells only when they engage in intimate physical interaction. The cell biological correlate of this APC-T cell interaction is commonly referred to as the formation of an immunological synapse. In this review we aim to provide an overview of a novel cell-free antigen-presenting platform, i.e. virus-like particles (VLP) decorated with immune receptors of choice, which was devised to overcome the molecular and cell biological complexity of the APC side of the immunological synapse. In the past we have demonstrated that immune receptor-decorated VLP are able to activate, modulate, or abrogate antigen-specific T lymphocyte responses. Thus, antigen-specific VLP represent a valuable tool which might help to explore and understand the function of antigen-specific T lymphocytes in more detail and might thus open new avenues for the modulation of pathologic T lymphocyte responses, e.g. for the treatment of allergic diseases.