Abstracts (complete list) - Wissenschaft Online

Annette Busch, Thomas Quast, Waldemar Kolanus, Percy Knolle, Andreas Limmer
Transfer of T cell surface molecules to Dendritic cells upon T
cell priming involving two distinct mechanisms differing in
quality and time
The adaptive immune response is initiated in secondary lymphoid organs by contact
between antigen-presenting cells (APCs) and antigen-specific CD4+ T cells. This
activation is characterized by multiple antigen recognition events that comprise the
interaction of both cell types through various molecules. In addition to the exchange of
costimulatory signals and cytokines the cells transfer cell surface molecules. To date
this is reported only as a unidirectional process of transfer from APC surface molecules
to the T cell. Here we describe for the first time the transfer of human and murine T cell
surface receptors to the APC. This transfer occurs in two phases that differ in quality
and time. The first set of molecules is transferred rapidly after T–APC contact, is cell–
cell contact-dependent, bound in an acid wash-resistant form to the cell surface and
resembles a mechanism described as trogocytosis, whereupon the APC actively gnaws
membrane fragments from the T cell membrane. The second set of T cell molecules is
exchanged after T cell activation (>16h), is non-covalently bound (acid wash sensitive)
and is transferred in a cell–cell contact-independent mode, resembling molecule
exchange via exosomes. The transferred molecules may have an important role in APC
conditioning and immunoregulation since they include the T cell receptor (TCR), CD3
and costimulatory molecules. Murine dendritic cells (DCs) loaded with T cell surface
molecules from ovalbumin (OVA)-specific CD4+ T cells by antigen-specific interaction
were less efficient in priming naïve CD4+ T cells of the same specificity. The great
amount of transgenic TCR on the DC surface may be responsible for the reduced
activation of the T cells by masking the antigen-bearing MHC molecules for access of
following antigen-specific CD4+ T cells. These findings may indicate an important role of
transferred T cell molecules to APC in the intraclonal competition of T cells for APC
access.