title: T cell receptor aggregation, but not dimerization, induces increased cytosolic calcium concentrations and reveals a lack of stable association between CD4 and the T cell receptor.
abstract: Exposure of T94, a CD4+ V beta 8-expressing murine Th cell clone, or immediately ex vivo CD4+ T cells to deaggregated, bivalent antibodies specific for either the TCR or CD3 failed to induce an increase in [Ca2+]i, or activation of phosphatidylinositol hydrolysis unless cross-linked with a secondary anti-Ig antibody. In contrast, we show that a combination of two mAb directed against different components of the TCR/CD3 complex (145.2C11, anti-CD3 epsilon and F23.1, anti-V beta 8) successfully induce second messenger formation, that is, without any requirement for a secondary antibody. This requirement for either a secondary antibody or two independent bivalent antibodies to activate second messenger production in T cells suggested that the signal transduction apparatus may be activated by multiple TCR/CD3 complexes being brought together on the T cell surface. This was supported by the observation that conditions inducing increased T cell [Ca2+]i through the TCR/CD3 complex also resulted in aggregation of the TCR/CD3 complex on the T cell surface. Conversely, binding of anti-TCR/CD3 antibodies to the T cell under conditions that did not induce increased [Ca2+]i also failed to induce surface TCR/CD3 redistribution. Cross-linking of the CD4 accessory molecule on T94 also resulted in increased [Ca2+]i, with kinetics similar to those observed after TCR/CD3 oligomerization. CD4 is involved in the recognition of invariant regions of MHC class II during Ag presentation and has been proposed to be associated with TCR/CD3 in the absence of Ag. Aggregation of TCR/CD3 and subsequent second messenger formation was achieved by combinations of mAb to distinct determinants within the complex due to the stable association of these determinants within the T cell membrane. We therefore assessed the functional association of CD4 with the TCR/CD3 complex by examining whether a combination of mAb directed against CD4 and CD3 or TCR induced second messenger formation. We found that anti-CD4 in combination with F23.1 or with 145.2C11 failed to induce increases in [Ca2+]i. Furthermore, mAb to CD4 failed to inhibit the increase in [Ca2+]i observed with the combination of 145.2C11 and F23.1. We therefore conclude that CD4 is not stably associated with TCR or CD3 in the absence of Ag/MHC class II composites.
authors.affiliation: Department of Microbiology and Immunology, McGill University, Montreal, Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Ratcliffe
authors.forename: K M
authors.initials: KM
authors.lastname: Coggeshall
authors.forename: M K
authors.initials: MK
authors.lastname: Newell
authors.forename: M H
authors.initials: MH
authors.lastname: Julius
mesh_terms: D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism*; D017252:CD3 Complex; D015704:CD4 Antigens / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D008198:Lymph Nodes / Q000166:cytology; D046911:Macromolecular Substances; D011940:Receptor Aggregation; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000502:physiology*; D006377:T-Lymphocytes, Helper-Inducer / Q000502:physiology
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D015704:CD4 Antigens; D046911:Macromolecular Substances; D011948:Receptors, Antigen, T-Cell; D002118:Calcium