Sébastien Calbo

Critical Role of TLR2 and TLR4 in Autoantibody Production and Glomerulonephritis in lpr Mutation-Induced Mouse Lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by pathogenic autoantibodies directed against nuclear Ags and immune complex deposits in damaged organs. Environmental factors have been thought to play a role in the onset of the disease. The recognition of these factors is mediated by TLRs, in particular TLR2 and TLR4 which bind pathogen-associated molecular patterns of Gram+ and Gram− bacteria, respectively. We attempted to determine the role of these TLRs in SLE by creating TLR2- or TLR4-deficient C57BL/6lpr/lpr mice. These mice developed a less severe disease and fewer immunological alterations. Indeed, in C57BL/6lpr/lpr-TLR2 or -TLR4-deficient mice, glomerular IgG deposits and mesangial cell proliferation were dramatically decreased and antinuclear, anti-dsDNA, and anti-cardiolipin autoantibody titers were significantly reduced. However, the response against nucleosome remained unaffected, indicating a role of TLR2 and TLR4 in the production of Abs directed against only certain categories of SLE-related autoantigens. Analysis of B cell phenotype showed a significant reduction of marginal zone B cells, particularly in C57BL/6lpr/lpr-TLR4-deficient mice, suggesting an important role of TLR4 in the sustained activation of these cells likely involved in autoantibody production. Interestingly, the lack of TLR4 also affected the production of cytokines involved in the development of lupus disease.

Efficient Binding of Reduced Peptide Bond Pseudopeptides to Major Histocompatibility Complex Class I Molecule

Reduced peptide bond pseudopeptide analogues have been examined for their ability to bind murine class I molecules of the major histocompatibility complex (MHC). Eight pseudopeptide analogues of an antigenic peptide derived from Plasmodium berghei (H-Ser-Tyr-Ile-Pro-Ser-Ala-Glu-Lys-Ile-OH) were obtained by systematically replacing one peptide bond at a time by a reduced peptide bond (CH-NH). The resulting analogues were then tested for their binding to a recombinant single chain SC-Kd class I molecule. The comparative results show that five analogues can efficiently mimic the parent peptide while the introduction of the reduced bond between P3-P4, P7-P8, and P8-P9 is deleterious for SC-Kd binding. The fact that more stable pseudopeptides containing reduced peptide bonds can bind major histocompatibility complex molecules is of great interest for the design of peptidomimetics with potential therapeutical properties. Such peptide analogues may prove useful for the development of peptide-based cytotoxic T lymphocyte vaccines.

Active Ca2+/Calmodulin-Dependent Protein Kinase IIγB Impairs Positive Selection of T Cells by Modulating TCR Signaling

T cell development is regulated at two critical checkpoints that involve signaling events through the TCR. These signals are propagated by kinases of the Src and Syk families, which activate several adaptor molecules to trigger Ca2+ release and, in turn, Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation. In this study, we show that a constitutively active form of CaMKII antagonizes TCR signaling and impairs positive selection of thymocytes in mice. Following TCR engagement, active CaMKII decreases TCR-mediated CD3ζ chain phosphorylation and ZAP70 recruitment, preventing further downstream events. Therefore, we propose that CaMKII belongs to a negative-feedback loop that modulates the strength of the TCR signal through the tyrosine phosphatase Src homology 2 domain-containing phosphatase 2 (SHP-2).

Antitumor vaccination using a major histocompatibility complex (MHC) class I-restricted pseudopeptide with reduced peptide bond

Synthetic peptides have raised a considerable interest in the fields of vaccines and immunotherapy. The authors previously introduced modifications into the peptide backbone of the H-2Kd-restricted epitope CW3. One of these pseudopeptides, C7, bound to Kd with an affinity identical to the parent peptide and was recognized by T cells specific for the parent peptide. The authors now show that this analog has an increased resistance to trypsin and displays an extended half-life in serum. The authors further tested its immunogenicity both in vitro and in vivo and found that cytotoxic T lymphocytes (CTL) induced against the peptide analog recognize the parent peptide. Moreover, analysis of T-cell receptor rearrangements by Immunoscope software revealed that C7-induced CTL display the hallmarks of the response against the parental epitope CW3. Administration of the pseudopeptide into DBA/2 mice induces a protective immune response against a lethal challenge with tumor cells expressing the parent peptide. Therefore, modifications in the backbone of antigenic peptides can decrease protease susceptibility while preserving immunogenicity. Such peptide analogues may therefore prove useful for the development of new therapeutic tools aimed at eradicating pathogens or tumors.

Cutting Edge: CD4-Independent Development of Functional FoxP3+ Regulatory T Cells

The CD4 coreceptor is mandatory for the differentiation and function of conventional MHC class II-restricted T cells, but little is known about its contribution in regulatory T cells (Tregs). We thus investigated the Treg compartment in mice lacking CD4. CD3+CD8−FoxP3+ cells were readily detected in the periphery of CD4−/− mice, where their percentages were even increased as compared with wild-type animals. These cells had a classical CD25+CD152+GITR+ Treg phenotype, were enriched in memory-type Tregs, and displayed a diversified TCR repertoire. Functionally, CD4−/− Tregs were equally as suppressive as CD4+/+ Tregs in vitro as well as in vivo. Hence, the CD4 coreceptor is dispensable for the generation and function of FoxP3+ Tregs. Furthermore, CD3+CD8−FoxP3+ Tregs were also found to develop in the absence of both CD4 and MHC-II molecules, demonstrating that the generation of Tregs can occur independently of MHC-II recognition.