Sustained signaling leading to T cell activation results from prolonged T cell receptor occupancy. Role of T cell actin cytoskeleton.
Using antigen-specific T cell clones and peptide-pulsed antigen-presenting cells (APCs) we investigated the mechanisms that lead to sustained signaling, known to be required for activation of effector function. Four lines of evidence indicate that the T cell actin cytoskeleton plays a crucial role in T cell activation by antigen-pulsed APCs, but is not required when T cell receptor (TCR) is cross-linked by soluble antibodies. First, addition of antibodies to the major histocompatibility complex molecules recognized by the TCR aborts the ongoing intracellular calcium concentration ([Ca2+]i) increase in performed T-APC conjugates, indicating that the sustained signaling requires the continuous occupancy of TCR. Second, time-lapse image recording shows that T lymphocytes conjugated to peptide-pulsed APCs undergo a sustained [Ca2+]i increase, which is accompanied by the formation of a large and changing area of contact between the two opposing membranes. Third, drugs that disrupt the actin cytoskeleton, Cytochalasin D and and C2 Clostridium botulinum toxin induce a rapid block of [Ca2+]i rise, coincident with a block of the cyclic changes in T cell shape. Finally, the addition of Cytochalasin D or of anti-MHC antibodies to preformed conjugates inhibits interferon gamma production in an 1-antigen dose- and time-dependent fashion. These results identify T cell actin cytoskeleton as a major motor for sustaining signal transduction and possibly for driving TCR cross-linking and offer an explanation for how T cells equipped with low affinity TCR can be triggered by a small number of complexes on APCs.
Basel Institute for Immunology, Switzerland.
S
S
Valitutti
M
M
Dessing
K
K
Aktories
H
H
Gallati
A
A
Lanzavecchia
D000199:Actins / Q000378:metabolism*; D000818:Animals; D000954:Antigens, Surface / Q000276:immunology; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*
D000199:Actins; D000954:Antigens, Surface; D011948:Receptors, Antigen, T-Cell