CELLULAR IMMUNOLOGY 141, 1-9 (1992) Potentiation of Transmembrane Signaling by Cross-Linking of Antibodies against the p Chain of the T Cell Antigen Receptor of JURKAT T Cells MAHMOOD JEDDI-TEHRANI,* SEK C. CHOW,? IGNACIO J. ANSOTEGUI,* MIKAEL JONDAL.* AND HANS WIGZELL* Departments of *Immunology and t Toxicology, Karolinska Institute, Box 60400, Stockholm, Sweden Received February 5, 1991; accepted December 5, 1991 Three monoclonal antibodies (mAb) 2D1,3B9, and 3B12 were produced by immunizing BALB/ c mice with JURKAT cells. ThesemAb induce comodulation of the TCR/CD3 complex expressed on JURKAT cells, but do not react with the CD3- JURKAT variant, J.RT3.T3.1. Immunopre- cipitation studies with detergent-solubilized JURKAT cell lystes indicate that these mAb react with proteins having characteristics of the TCR molecules. Their low reactivity with peripheral blood mononuclear cells (PBMC)andlackof reactivity with otherCD3+ T cell linessuggest that they may be anti-idiotypic mAb. Results from binding inhibition assays, reactivity with PBMC, and generation of transmembrane signals suggestthat these three anti-TCR mAb recognized different epitopes on the TCR p chain of JURKAT cells. Although the three mAb are capable of inducing the production of inositol phosphates and cytosohc free Ca’+ increasein JURKAT cells, their stimulatory capacities vary and are lower than that observed by anti-CD3 antibody (OKT3) stimulation. However, crosslinking thesemAb with rabbit antimouse immunoglobuhns potentiates the stimulatory response to comparable levels induced by OKT3. These mAb could be useful as tools to study Vp8” T cells in relation to antigen-specific activation. a 1992 Academic press, Inc. INTRODUCTION The human T-cell antigen receptor (TCR) presenton mature T lymphocytes consists of two heterodimeric polypeptide chains (a and ,B) noncovalently associatedwith the CD3 molecular complex (l-5). This TCR/CD3 complex is known to play a major role in the initiation of T cell activation (6-10). Ligation of the TCR/CD3 complex has been shown to result in cell proliferation, cytotoxic function, or the production of lymphokines ( 1l- 13). Analysis of antibodies against the TCR/CD3 complex and their activation potentials has led to the characterization of several stepsof T-cell activation via the TCR/CD3 complex. One of the earliest events involved in T-cell activation is the hydrolysis of inositol lipids (14). This in turn generatestwo putative second messengers, inositol 1,4,5-trisphosphate (Ins( 1,4,5)P,) and diacylglycerol. Ins( 1,4,5)P, induces the release of Ca*+ from intracellular stores ( 13, 15) while diacylglycerol activates protein kinase C to phosphorylate cellular proteins ( 16). mAb directed against different epitopes on the TCR/CD3 complex may have dif- ferent stimulatory potentials (17) and a requirement of accessoryceils (AC) would normally be necessary to fully activate some T cells. This is especiallytrue for peripheral 0008-8749192 $3.00 Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form resewed.