Molecular mechanisms in the TCR (TCR alpha beta-CD3 delta epsilon, gamma epsilon) interaction with zeta 2 homodimers: clues from a 'phenotypic revertant' clone

Anti-inflammatory and antinociceptive effects of the selective cannabinoid CB2 receptor agonist ABK5

Cannabinoid receptors are a potential target for anti-inflammatory and pain therapeutics. There are two subtypes, CB1 and CB2, and Δ9-tetrahydrocannabinol activates both of them, providing an analgesic effect but also psychoactive side effects. The psychoactive side effects are considered to be caused by activation of CB1, but not CB2. ABK5 is a CB2 subtype selective agonist that has a very different structure from known cannabinoid receptor agonists. Here, we report anti-inflammatory effects of ABK5 using the T-cell line Jurkat cells, and antinociceptive effect in an inflammatory pain model in rats. Production of the cytokines IL-2 and TNF-α was measured in stimulated Jurkat cells and MOLT-4 cells, and CXCL12-mediated chemotaxis of Jurkat cells was evaluated by a transwell migration assay. Anti-inflammatory and antinociceptive effects of ABK5 were also evaluated in a hindpaw CFA model in rats. ABK5 significantly decreased production of IL-2 and TNF-α measured as both mRNA and protein levels, and reduced chemotaxis towards CXCL12. It also attenuated edema and increased mechanical threshold in the hindpaw of CFA-treated rats. These results suggest that ABK5 is a good lead compound for the development of potential anti-inflammatory and analgesic agents.

Human congenital T-cell receptor disorders

Immunodeficiencies of most T-cell receptor (TCR) components (TCRID) have been reported in almost 40 patients worldwide who have also, at times, shown signs of autoimmunity. We updated their clinical, immunological, and molecular features with an emphasis on practical diagnosis, as the range of the disorder grows in complexity with new partial defects. Cellular and animal models are also reviewed and in some cases reveal their limitations for predicting TCRID immunopathology.

Some hints concerning the shape of T-cell receptor structures

Several models are proposed for T-cell antigen receptor (TCR) assembly and structure. However, there is little experimental data favouring directly either one or the other(s). The minimal complex appears to be composed of a TCRalphabeta/CD3deltaepsilon,gammaepsilon/zeta2 structure but at the cell membrane, multimers of this minimal structure may be formed. Quantitative cytofluometry has suggested three CD3epsilon chains for two TCRbeta (or TCRdelta) chains/complex. Such data should be repeated with monoclonal antibodies (MoAb) against extracellular (EC) parts of CD3delta or CD3gamma chains. In the present review, we have compared the TCR/CD3 assembly of pre-TCR, TCRgammadelta and TCRalphabeta containing complexes, and analysed the reactivity of antibodies (Abs) against the EC part of CD3delta chains. Our data suggest an alternative assembly pathway and structure of TCR/CD3 complexes.

On the role of CD3delta chains in TCRgammadelta/CD3 complexes during assembly and membrane expression

The present study was performed in order to analyze whether T-cell receptor (TCR)/CD3 assembly, intracellular transport and surface expression are carried in a similar way in alphabeta-and gammadelta-T cells. By means of optimal immunoprecipitation conditions with 35S-methionine/cysteine- or biotin-labelled TCR/CD3 proteins from alphabeta- or gammadelta-T-lymphoma-cell lines, as well as TCRgammadelta cDNA transfectants, it was found that CD3delta chains associate less strongly with TCRgammadelta heterodimers compared to TCRalphabeta heterodimers. This preferential reactivity of CD3delta chains appears to be structural and not owing to differences in gammadelta- versus alphabeta-T-cell intracellular environments. Our results are in accordance firstly, with data from CD3delta-deficient mice, which have gammadelta-T cells but no alphabeta-T cells, secondly with the suggested role of CD3delta chains in the positive selection of alphabeta-T cells, a process apparently not followed by gammadelta-T cells, and lastly with the differential roles of CD3delta chains versus CD3gamma chains, explaining the maintenance of two CD3delta and CD3gamma genes after the duplication from a CD3delta/gamma gene present in avians. The impaired reactivity of CD3delta chains with TCRgammadelta heterodimers seems to be owing to a less efficient association with TCRgamma chains. In contrast, CD3delta chains interact as strongly with TCRdelta chains as do CD3gamma chains with both TCRgamma and TCRdelta chains. These data may explain, at the molecular levels, why surface TCR/CD3 expression levels are impaired in gammadelta-T cells from CD3gamma-deficient mice but not from CD3delta-deficient mice.

Molecular modelling and endoplasmic reticulum retention of mutated TCR/CD3 complexes

T cell receptor (TCR)/CD3 complex assembly takes place in the endoplasmic reticulum (ER). Normal TCR/CD3 complexes egress from the ER to the cis-Golgi, where the interaction with zeta2 homodimers occurs. This interaction leads to further uncontrolled transport of TCR/CD3/zeta molecules to the cell surface. The purpose of the present experiments was to determine firstly the basis for the impact of the Phe195/216 --> Val mutations on TCR/CD3 expression in Jurkat cells, and secondly why mutated J79-cell TCRalphabeta/CD3 hexamers are prevented from interacting with zeta2 homodimers. We found that Phe --> Val mutations cause serious perturbations in a so far undefined hydrophobic area formed by the two Phe195/216 on beta-strand F and aromatic/large hydrophobic amino acids on neighboring beta-strands B and A in Calpha and Cbeta domains, respectively. In addition, TCR/CD3 hexamers and zeta2 homodimers colocalize in normal Jurkat T cells, in revertant J79r58 cells, and in J79 cells transfected with wild-type TCRalpha cDNA but not in J79 mutant cells (confocal microscopy). Furthermore, mutated TCR/CD3 complexes seem to be actively retained in the ER in J79 cells but not in revertant J79r58 cells by a nondominant mechanism. We propose that a hitherto undefined ER-retention molecule controls both the protein structure and egress of TCR/CD3 complexes from the ER of alphabeta and gammadelta T cells.

Dissection of the role of CD3gamma chains in profound but reversible T-cell receptor down-regulation

T-lymphocyte activity in the immune system is regulated by the quantity of surface membrane T-cell antigen receptors (TCR). The amount of surface-bound TCR is dependent on the rate of [1] biosynthesis, assembly and intracellular transport of the individual chains composing the TCR/CD3 complex and [2] the internalization and recycling of the receptors. The TCR-ligand interaction augments receptor internalization. In the present paper, we have studied short- and long-term down-regulation of TCR/CD3 complexes with monoclonal anti-TCR/CD3 antibodies, and attempted to determine which component(s) of the TCR/CD3 complex are responsible for these two phenomena. Our data indicate that short- and long-term down-regulation is mediated by different mechanisms, and that the extracellular and/or transmembrane regions of CD3gamma molecules appear to play an important role in chronic TCR/CD3 down-regulation and subsequent deficient re-expression. These results may have important implications for the understanding of induction of T-cell tolerance or anergy.