Emerging Bordetella pertussis Strains Induce Enhanced Signaling of Human Pattern Recognition Receptors TLR2, NOD2 and Secretion of IL-10 by Dendritic Cells.

Vaccines against pertussis have been available for more than 60 years. Nonetheless, this highly contagious disease is reemerging even in countries with high vaccination coverage. Genetic changes of Bordetella pertussis over time have been suggested to contribute to the resurgence of pertussis, as these changes may favor escape from vaccine-induced immunity. Nonetheless, studies on the effects of these bacterial changes on the immune response are limited. Here, we characterize innate immune recognition and activation by a collection of genetically diverse B. pertussis strains isolated from Dutch pertussis patients before and after the introduction of the pertussis vaccines. For this purpose, we used HEK-Blue cells transfected with human pattern recognition receptors TLR2, TLR4, NOD2 and NOD1 as a high throughput system for screening innate immune recognition of more than 90 bacterial strains. Physiologically relevant human monocyte derived dendritic cells (moDC), purified from peripheral blood of healthy donors were also used. Findings indicate that, in addition to inducing TLR2 and TLR4 signaling, all B. pertussis strains activate the NOD-like receptor NOD2 but not NOD1. Furthermore, we observed a significant increase in TLR2 and NOD2, but not TLR4, activation by strains circulating after the introduction of pertussis vaccines. When using moDC, we observed that the recently circulating strains induced increased activation of these cells with a dominant IL-10 production. In addition, we observed an increased expression of surface markers including the regulatory molecule PD-L1. Expression of PD-L1 was decreased upon blocking TLR2. These in vitro findings suggest that emerging B. pertussis strains have evolved to dampen the vaccine-induced inflammatory response, which would benefit survival and transmission of this pathogen. Understanding how this disease has resurged in a highly vaccinated population is crucial for the design of improved vaccines against pertussis.

Blimp-1 homolog Hobit identifies effector-type lymphocytes in humans.

Human cytomegalovirus (CMV) induces the formation of effector CD8(+) T cells that are maintained for decades during the latent stage of infection. Effector CD8(+) T cells appear quiescent, but maintain constitutive cytolytic capacity and can immediately produce inflammatory cytokines such as IFN-γ after stimulation. It is unclear how effector CD8(+) T cells can be constitutively maintained in a terminal stage of effector differentiation in the absence of overt viral replication. We have recently described the zinc finger protein Homolog of Blimp-1 in T cells (Hobit) in murine NKT cells. Here, we show that human Hobit was uniformly expressed in effector-type CD8(+) T cells, but not in naive or in most memory CD8(+) T cells. Human CMV-specific but not influenza-specific CD8(+) T cells expressed high levels of Hobit. Consistent with the high homology between the DNA-binding Zinc Finger domains of Hobit and Blimp-1, Hobit displayed transcriptional activity at Blimp-1 target sites. Expression of Hobit strongly correlated with T-bet and IFN-γ expression within the CD8(+) T-cell population. Furthermore, Hobit was both necessary and sufficient for the production of IFN-γ. These data implicate Hobit as a novel transcriptional regulator in quiescent human effector-type CD8(+) T cells that regulates their immediate effector functions.