Current Biology
Volume 4, Issue 7, July 1994, Pages 584-595
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Research Paper
Antigen recognition by helper T cells elicits a sequence of distinct changes of their shape and intracellular calcium

https://doi.org/10.1016/S0960-9822(00)00130-5Get rights and content

Abstract

Background: Helper T-cell activation is initiated in vivo when the T-cell receptor complex recognizes an antigen fragment associated with MHC class II molecules on the surface of an antigen-presenting cell. In most previous studies of this phenomenon, T cells were stimulated not with antigen-presenting cells, but with CD3-specific antibodies. This approach provided considerable understanding of the cascade of molecular events triggered by T-cell receptor stimulation. However, the specific consequences of cell–cell interactions are still poorly understood. We therefore used a dual imaging system that provides simultaneous transmission and fluorescence images to study the morphological changes and variations of intracellular calcium concentration ([Ca2+]i) triggered in a human CD4+ antigen-specific T-cell clone in response to antigen presented by a class II-transfected murine fibroblast.

Results T cells loaded with the Ca2+-sensitive fluorescent dye Fura-2 were individually monitored for half an hour following their contact with a monolayer of antigen-pulsed antigen-presenting cells. The response was found to have three distinct phases. During the first few minutes after contact, the T cell moves over the antigen-presenting cells, as if ‘scanning’ them. After several minutes, an oscillating [Ca2+]i response begins, accompanied by the immobilization of the cell and the retraction of pseudopodia. This rounding-up was probably Ca2+-dependent, as it could also be triggered by ionomycin or thapsigargin. Later during the [Ca2+]i response, the T cell becomes flattened and further elongated, suggesting increased adhesion to antigen-presenting cells.

Conclusions The physiological signal for T-cell activation, antigen recognition, is a three-step process reminiscent of the three steps previously observed in the interaction between neutrophils and endothelial cells. During these successive steps, a mobile, weakly interacting T cell is transformed into an immobile cell fully engaged in the activation pathway. Thus, antigenic recognition is not instantaneous, but evolves slowly by progressive amplification of the signal given by a few antigen molecules, eventually resulting in T-cell activation.

Section snippets

Background:

The physiological signal necessary for helper T-cell activation is delivered by a prolonged interaction between the T cell and an antigen-presenting cell (reviewed in [1]). The antigen-specific signal begins with the recognition by the T-cell receptor of an antigen fragment associated with a MHC class II molecule. This triggers a cascade of transduction events, initiated by the CD3 molecule associated with the T-cell receptor (see [2] for review). Other interactions between the T cell and

First phase of the antigen-presenting cell–T cell interaction

When T cells were allowed to settle on a monolayer of L cells in the absence of antigen, most of the T cells were roughly spherical and remained so throughout the duration of the experiment. Under these conditions, adhesion of T cells to L cells was never stable, as the T cells could move when the dish was tipped slightly. Some T cells presented deformations, but these did not appear related to interaction with L cells. The magnitude of these deformations and the percentage of deformed T cells

Discussion

In this paper, we have studied the interaction between helper T lymphocytes and antigen-presenting cells in a simplified biological system (murine artificial antigen-presenting cells, human T cells). The advantage of this system is that cell–cell interactions in the absence of antigen were too weak to allow stable adhesion between the two cell types, and therefore could be considered negligible. The first events observed when the antigen was presented were therefore necessarily a direct

Cells

T-cell clone P28D (P28 cells), specific for diphtheria toxoid (DT) was derived from a HLA-DR6/7 healthy individual as previously described [37]. The clone was propagated in complete culture medium (RPMI 1640 supplemented with 5 % pooled human AB serum, 2 mM L-glutamine, 1 mM Na pyruvate, 50 U ml–1 penicillin, and 50 μgm l–1 streptomycin) by periodic restimulation with the antigen presented by an autologous Epstein-Barr virus transformed B-cell line. Medium containing interleukin-2 (IL-2, final

Acknowledgements

This work was supported by grants from Centre National de la Recherche Scientifique, including an ATIPE grant, and Université Pierre et Marie Curie. E.D. was supported by a grant from the Association de Recherche contre le Cancer. We thank Y.P. Tan for the filter exchange system, C. Randriamampita, M.A. Deugnier and P. Deterre for their comments on the manuscript.

E. Donnadieu, A. Trautmann (corresponding author), Laboratoire de Neurobiologie, CNRS URA 1857, Ecole Normale Supérieure, 46, rue d’Ulm, 75005 Paris, France.

G.Bismuth, Laboratoire d’Immunologie Cellulaire et Tissulaire, CNRS URA 625, CERVI, Centre Hospitalier Pitié-Salpêtrière, 75013 Paris, France.

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    E. Donnadieu, A. Trautmann (corresponding author), Laboratoire de Neurobiologie, CNRS URA 1857, Ecole Normale Supérieure, 46, rue d’Ulm, 75005 Paris, France.

    G.Bismuth, Laboratoire d’Immunologie Cellulaire et Tissulaire, CNRS URA 625, CERVI, Centre Hospitalier Pitié-Salpêtrière, 75013 Paris, France.

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