The conformation of the CD3 complex on T lymphocytes is modified by calcium ions.
While calcium ions are known to play a prominent role in signal transduction in the activation of T lymphocytes, its mechanism of action, target and function have not been elucidated. One crucial event in the calcium-dependent process is the activation of the CD3 complex, and this, too, is not understood. While studying the release of Ca2+ from intracellular stores by several monoclonal antibodies (mAb) against CD3, we found that one of them, mAb 141, was ineffective unless free Ca2+ was present in the external medium. By flow cytometric analysis of the binding of this mAb to Jurkat T cells and peripheral blood lymphocytes we showed that 141 does not recognize the CD3 complex when external Ca2+ is chelated by EGTA. The binding was restored by addition of Ca2+ but not Mg2+. Finally at least one subunit of the CD3 complex displayed a modified electrophoretic migration rate when immunoprecipitated by Leu-4 in the absence of external free Ca2+. These results suggest that the conformation of the CD3 complex depends on Ca2+, the epitope recognized by 141 being concealed at low Ca2+ concentration.
Breittmayer
J P
JP
INSERM U210, Faculté de Médecine (Pasteur), Nice, France.
Schaffar
L
L
Bourel
D
D
Fehlmann
M
M
D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D017252:CD3 Complex; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D011233:Precipitin Tests; D011487:Protein Conformation; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D011948:Receptors, Antigen, T-Cell; D002118:Calcium