ABSTRACT
INTRODUCTION: In patients, a transient decrease in peripheral blood lymphocyte counts was observed following intraperitoneal administration of the trifunctional monoclonal antibody catumaxomab (anti-human EpCAM x anti-human CD3). The aim of this study was to clarify the observed effect in a preclinical mouse model and to analyse the related mechanism of action in vitro. MATERIALS AND METHODS: A related antibody, BiLu (antihuman EpCAM x anti-mouse CD3), was administered to mice and blood leukocytes were analysed. In vitro studies measured activation and cytokine secretion from human peripheral blood mononuclear cells (PBMC). For the analysis of T cell adhesion, PBMC were preincubated with catumaxomab and then co-cultured with human endothelial cells (HUVEC); T cell adhesion was assessed in the presence or absence of endothelial cell preactivation by TNFα. Adherent T cells were determined by flow cytometry. RESULTS: Treatment of mice with BiLu resulted in a dosedependent transient decrease in CD3+ T cells (both CD4+ and CD8+) that returned to the normal range within 48 h. Catumaxomab physiologically activated T cells in vitro (increased CD69 expression) and induced cytokine release (TNFα, IFNγ). TNFα increased expression of adhesion molecules CD54 and CD62E on endothelial cells. Furthermore, catumaxomab dose-dependently enhanced adhesion of T cells to endothelial cells. Adhesion was further increased when endothelial cells were preactivated with TNFα. CONCLUSIONS: Catumaxomab increases adhesion of T cells to endothelial cells due to antibody-mediated activation of T cells and production of T cell cytokines that up-regulate endothelial cell adhesion molecules. These results provide a mechanistic rationale for the transient, reversible decrease in lymphocyte counts observed following catumaxomab administration in patients, which is likely to be due to redistribution of lymphocytes (AU)
Subject(s)
Animals , Tumor Necrosis Factor Receptor Superfamily, Member 7/administration & dosage , Tumor Necrosis Factor Receptor Superfamily, Member 7/analysis , Tumor Necrosis Factor Receptor Superfamily, Member 7/blood , Tumor Necrosis Factor Receptor Superfamily, Member 7/chemical synthesis , Tumor Necrosis Factor Receptor Superfamily, Member 7/classification , Tumor Necrosis Factor Receptor Superfamily, Member 7/deficiency , Tumor Necrosis Factor Receptor Superfamily, Member 7 , Tumor Necrosis Factor Receptor Superfamily, Member 7/toxicityABSTRACT
El receptor para antígeno de los linfocitos T (TCR) es un complejo multiproteíco responsable de la activación y regulación de la respuesta inmune adaptativa. Este receptor muestra una gran especificidad y sensibilidad, a la vez que tiene una baja afinidad por su ligando. El ligando del TCR es un complejo formado por el péptido antigénico y una molécula del complejo principal de histocompatibilidad (MHC). Es más, los linfocitos T responden a antígeno en un rango muy amplio de concentraciones. Esto es, los linfocitos T continúan dando una respuesta aumentada a concentraciones de antígeno que exceden en varios órdenes de magnitud la concentración activadora mínima. La estequiometría y organización del TCR en la membrana han estado bajo intenso escrutinio porque pueden ser clave para explicar sus propiedades paradójicas. Esta revisión subraya la existencia de nuevos datos que indican que el TCR se presenta en linfocitos T intactos y en reposo como una mezcla variable de formas monovalentes (con sólo un sitio de unión para el ligando) y formas multivalentes de distinto grado. Estos resultados contrastan con datos anteriores de estequiometría del TCR obtenidos por procedimientos bioquímicos. No obstante, la mayor parte de estas discrepancias pueden deberse al efecto de distintos detergentes en la integridad del receptor. Aquí discutimos un modelo donde los complejos multivalentes del TCR son los responsables de dotar a los linfocitos T de sensibilidad a antígeno porque son activados por bajas concentraciones de antígeno, mientras que los complejos monovalentes son los responsables del amplio rango dinámico (AU)
The T cell antigen receptor (TCR·CD3) is a multi-subunit complex responsible for triggering an adaptive immune response. It shows high specificity and sensitivity while having a low affinity for the ligand. Furthermore, T cells respond to antigen over a wide concentration range. The stoichiometry and architecture of TCR·CD3 in the membrane have been under intense scrutiny because they might be key to explaining its paradoxical properties. This review highlights new evidence that TCR·CD3 is found on intact, unstimulated T cells in monovalent (one ligand-binding site per receptor) as well as in several distinct multivalent forms. This is in contrast to the TCR·CD3 stoichiometries determined by several biochemical means, but these data can be explained by the effects of different detergents on the integrity of the receptor. Here, we discuss a model in which the multivalent receptors are important for the detection of low concentrations of ligand, and therefore confer sensitivity, whereas the co-expressed monovalent TCR·CD3s allow a wide dynamic range (AU)
