Antigen-dependent and -independent Ca2+ responses triggered in T cells by dendritic cells compared with B cells.
Dendritic cells (DCs) are much more potent antigen (Ag)-presenting cells than resting B cells for the activation of naive T cells. The mechanisms underlying this difference have been analyzed under conditions where ex vivo DCs or B cells presented known numbers of specific Ag-major histocompatibility complex (MHC) complexes to naive CD4(+) T cells from T cell antigen receptor (TCR) transgenic mice. Several hundred Ag-MHC complexes presented by B cells were necessary to elicit the formation of a few T-B conjugates with small contact zones, and the resulting individual T cell Ca2+ responses were all-or-none. In contrast, Ag-specific T cell Ca2+ responses can be triggered by DCs bearing an average of 30 Ag-MHC complexes per cell. Formation of T-DC conjugates is Ag-independent, but in the presence of the Ag, the surface of the contact zone increases and so does the amplitude of the T cell Ca2+ responses. These results suggest that Ag is better recognized by T cells on DCs essentially because T-DC adhesion precedes Ag recognition, whereas T-B adhesion requires Ag recognition. Surprisingly, we also recorded small Ca2+ responses in T cells interacting with unpulsed DCs. Using DCs purified from MHC class II knockout mice, we provide evidence that this signal is mostly due to MHC-TCR interactions. Such an Ag-independent, MHC-triggered calcium response could be a survival signal that DCs but not B cells are able to deliver to naive T cells.
Laboratoire d'Immunologie Cellulaire, Centre National de la Recherche Scientifique UMR 7627, CERVI, 75013 Paris, France.
J
J
Delon
N
N
Bercovici
G
G
Raposo
R
R
Liblau
A
A
Trautmann
D000818:Animals; D017951:Antigen Presentation; D000941:Antigens / Q000502:physiology*; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002450:Cell Communication; D003713:Dendritic Cells / Q000502:physiology*; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D013601:T-Lymphocytes / Q000502:physiology*
D000941:Antigens; D011948:Receptors, Antigen, T-Cell; D002118:Calcium