Hanny Klaasse Bos

Antigen-Specific B Cells Reactivate an Effective Cytotoxic T Cell Response against Phagocytosed Salmonella through Cross-Presentation

Background The eradication of facultative intracellular bacterial pathogens, like Salmonella typhi, requires the concerted action of both the humoral immune response and the cytotoxic CD8+ T cell response. Dendritic cells (DCs) are considered to orchestrate the cytotoxic CD8+ T cell response via cross-presentation of bacterial antigens onto MHC class I molecules. Cross-presentation of Salmonella by DCs however, is accompanied by the induction of apoptosis in the DCs. Besides antibody production, B cells are required to clear Salmonella infection for other unknown reasons. Methodology/Principal Findings Here we show that Salmonella-specific B cells that phagocytose Salmonella upon BCR-ligation reactivate human memory CD8+ T cells via cross-presentation yielding a Salmonella-specific cytotoxic T cell response. The reactivation of CD8+ T cells is dependent on CD4+ T cell help. Unlike the DCs, B cell-mediated cross-presentation of Salmonella does not coincide with apoptosis. Conclusions/Significance B cells form a new player in the activation of the cytotoxic effector arm of the immune response and the generation of effective adaptive immunity in Salmonella infection.

CD5 costimulation induces stable Th17 development by promoting IL-23R expression and sustained STAT3 activation

IL-17-producing CD4(+) T helper (Th17) cells are important for immunity against extracellular pathogens and in autoimmune diseases. The factors that drive Th17 development in human remain a matter of debate. Here we show that, compared with classic CD28 costimulation, alternative costimulation via the CD5 or CD6 lymphocyte receptors forms a superior pathway for human Th17-priming. In the presence of the Th17-promoting cytokines IL-1β, IL-6, IL-23, and transforming growth factor-β (TGF-β), CD5 costimulation induces more Th17 cells that produce higher amounts of IL-17, which is preceded by prolonged activation of signal transducer and activator of transcription 3 (STAT3), a key regulator in Th17 differentiation, and enhanced levels of the IL-17-associated transcription factor retinoid-related orphan receptor-γt (ROR-γt). Strikingly, these Th17-promoting signals critically depend on CD5-induced elevation of IL-23 receptor (IL-23R) expression. The present data favor the novel concept that alternative costimulation via CD5, rather than classic costimulation via CD28, primes naive T cells for stable Th17 development through promoting the expression of IL-23R.

LEUCINE-58 IN THE PUTATIVE 5TH HELICAL REGION OF HUMAN INTERLEUKIN (IL)-6 IS IMPORTANT FOR ACTIVATION OF THE IL-6 SIGNAL TRANSDUCER, GP130

A model of the tertiary structure of human IL‐6, derived from the crystal‐structure of granulocyte‐colony stimulating factor, reveals a 5th helical region in the loop between the first and second α‐helix. To investigate the importance of this region for biological activity of IL‐6, residues Glu‐52, Ser‐53, Ser‐54, Lys‐55, Glu‐56, Leu‐58 and Glu‐60 were individually replaced by alanine. IL‐6·Leu‐58Ala displayed a 5‐fold reduced biological activity on the IL‐6‐responsive human cell lines XG‐1 and A375. This reduction in bioactivity was shown to be due to a decreased capacity of the mutant protein to trigger IL‐6 receptor‐α‐chain‐dependent binding to the IL‐6 signal transducer, gp130.

Identification of residues in the putative 5th helical region of human interleukin-6, important for activation of the IL-6 signal transducer, gp130

We have previously shown that L58 in the putative 5th helical region of human interleukin‐6 (IL‐6) is important for activation of the IL‐6 signal transducer gp130 [de Hon et al. (1995) FEBS Lett. 369, 187–191]. To further explore the importance of individual residues in this region for gp130 activation we have now combined Ala substitutions of residues E52, S53, S54, K55, E56, L58 and E60 with other substitutions in IL‐6, known to affect gp130 activation (Q160E and T163P). The combination mutant protein with L58A completely lost the capacity to induce the proliferation of XG‐1 myeloma cells, and could effectively antagonize wild type IL‐6 activity on these cells. Moreover, the data suggest that besides L58, S54 particularly, but also E52, S53, K55 and E56 contribute to gp130 activation.