Abstract B cells express the innate receptor, TLR9, which signals in response to unmethylated CpG sequences in microbial DNA. Of the two major classes of CpG-containing oligonucleotides, CpG-A appears restricted to inducing type 1 IFN in innate immune cells and CpG-B to activating B cells to proliferate and produce Abs and inflammatory cytokines. Although CpGs are candidates for adjuvants to boost innate and adaptive immunity, our understanding of the effect of CpG-A and CpG-B on B cell responses is incomplete. In this study we show that both CpG-B and CpG-A activated B cells in vitro to proliferate, secrete Abs and IL-6, and that neither CpG-B nor CpG-A alone induced type 1 IFN production. However, when incorporated into the cationic lipid, DOTAP, CpG-A, but not CpG-B, induced a type 1 IFN response in B cells in vitro and in vivo. We provide evidence that differences in the function of CpG-A and CpG-B may be related to their intracellular trafficking in B cells. These findings fill an important gap in our understanding of the B cell response to CpGs, with implications for the use of CpG-A and CpG-B as immunomodulators.
Abstract Visceral leishmaniasis (VL) is a potentially fatal disease transmitted by sand fly bites and caused by Leishmania (L. donovani/L. infantum) protozoa. Kupffer cells (KCs) are the liver embryonic resident macrophages (emKCs), characterized by Clec4f and Tim4 expression and their sessile behavior within the liver sinusoids. KCs maintain their numbers via self-proliferation during homeostasis but can be replaced by monocyte-derived cells (moKCs) during inflammation. In the murine VL model, KCs are important for both initial parasite growth and granuloma formation, the latter being associated with the eventual protective response. The objective of our study is to investigate KC proliferation, migration, death, and their replacement by moKCs in VL. We found that KC proliferation was enhanced at 19 d.p.i., while at 42 d.p.i. the granulomas cores contained mixed KC clonal lineages and were located outside the liver sinusoids. At the same time point, Clec4f and Tim4 expression was reduced, and we found evidence of KC apoptosis and ferroptosis. Parabiotic mice demonstrated KC populations that bore either congenic marker, and CCR2 −/−infected mice showed enhanced frequencies of emKCs, reduced frequencies of moKCs, and higher parasite loads compared to WT mice. Reduction of ferroptosis in BACH1 −/−mice resulted in lower frequencies of moKCs. Collectively, our data indicates that KCs migrate to the liver parenchyma to form granulomas, facilitating their activation by other immune cells, and that KC death results in their partial replacement by moKCs, contributing to increased parasite killing. Thus, KC heterogeneity is an important hallmark of hepatic resistance in VL. Funded by the Division of Intramural Research, NIAID.
Abstract Professional APCs present peptides to CD4+ T cells in the context of MHCII. To understand the dynamics of peptide-MHCII complexes in T cell-APC interaction, real-time visualization of these complexes is crucial. However, current reagents such as peptide specific MHCII antibodies do not allow one to probe peptide-MHCII dynamics during live interactions in vivo, as they also block T cell-APC interactions. Fluorescent tags such as green fluorescent protein (GFP) consist of more than 200 amino acids and have the potential of disrupting the functionality of the antigenic peptides. Therefore, we constructed an OVA(323–339) peptide containing a pro-fluorescent tetracysteine tag (CCPGCC) at the C-terminus with aminocaproic acid linker (OVACACA). First, we tested whether the addition of tag had an impact on T cell stimulation and found that OVACACA pulsed APCs could activate OTII cells to same degree as OVA(323–339). Secondly, we treated the APCs with an organoarsenic compound to switch on the fluorescence and measured the signal by flow cytometry. We showed that the fluorescent signal specifically was derived from OVACACA-MHCII, as neither MHCII−/− APCs pulsed with OVACACA, nor MHCII+/+ APCs pulsed with OVA(323–339) produced the same signal. We also tracked the fluorescent signal in OTII-DC cultures in vitro and detected that it was concentrated at the synapse over time. Altogether our findings suggest that tetracysteine tagged peptides can be used for tracking peptide-MHCII complexes during the interactions of primary mouse T cells and APCs and have the potential to be an alternative to MHCII tetramers to detect antigen specific T cells.
Neutrophils are first responders rapidly mobilized to inflammatory sites by a tightly regulated, nonredundant hierarchy of chemoattractants. These chemoattractants engage neutrophil cell surface receptors triggering heterotrimeric G-protein Gαi subunits to exchange GDP for GTP. By limiting the duration that Gαi subunits remain GTP bound, RGS proteins modulate chemoattractant receptor signaling. Here, we show that neutrophils with a genomic knock in of a mutation that disables regulator of G-protein signaling (RGS)-Gαi2 interactions accumulate in the bone marrow and mobilize poorly to inflammatory sites. These defects are attributable to enhanced sensitivity to background signals, prolonged chemoattractant receptor signaling, and inappropriate CXCR2 downregulation. Intravital imaging revealed a failure of the mutant neutrophils to accumulate at and stabilize sites of sterile inflammation. Furthermore, these mice could not control a nonlethal Staphylococcus aureus infection. Neutrophil RGS proteins establish a threshold for Gαi activation, helping to coordinate desensitization mechanisms. Their loss renders neutrophils functionally incompetent.
BACKGROUND: Severe malaria is associated with impaired nitric oxide (NO) synthase (NOS)–dependent vasodilation, and reversal of this deficit improves survival in murine models. Malaria might have selected for genetic polymorphisms that increase endothelial NO signaling and now contribute to heterogeneity in vascular function among humans. One protein potentially selected for is alpha globin, which, in mouse models, interacts with endothelial NOS (eNOS) to negatively regulate NO signaling. We sought to evaluate the impact of alpha globin gene deletions on NO signaling and unexpectedly found human arteries use not only alpha but also beta globin to regulate eNOS. METHODS: The eNOS-hemoglobin complex was characterized by multiphoton imaging, gene expression analysis, and coimmunoprecipitation studies of human resistance arteries. Novel contacts between eNOS and hemoglobin were mapped using molecular modeling and simulation. Pharmacological or genetic disruption of the eNOS-hemoglobin complex was evaluated using pressure myography. The association between alpha globin gene deletion and blood pressure was assessed in a population study. RESULTS: Alpha and beta globin transcripts were detected in the endothelial layer of the artery wall. Imaging colocalized alpha and beta globin proteins with eNOS at myoendothelial junctions. Immunoprecipitation demonstrated that alpha globin and beta globin form a complex with eNOS and cytochrome b5 reductase. Modeling predicted negatively charged glutamic acids at positions 6 and 7 of beta globin to interact with positively charged arginines at positions 97 and 98 of eNOS. Arteries from donors with a glutamic acid–to–valine substitution at beta globin position 6 (sickle trait) exhibited increased NOS-dependent vasodilation. Alpha globin gene deletions were associated with decreased arterial alpha globin expression, increased NOS-dependent vasodilation, and lower blood pressure. Mimetic peptides that targeted the interactions between hemoglobin and eNOS recapitulated the effects of these genetic variants on human arterial vasoreactivity. CONCLUSIONS: Alpha and beta globin subunits of hemoglobin interact with eNOS to restrict NO signaling in human resistance arteries. Malaria-protective genetic variants that alter the expression of alpha globin or the structure of beta globin are associated with increased NOS-dependent vasodilation. Targeting the hemoglobin-eNOS interface could potentially improve NO signaling in diseases of endothelial dysfunction such as severe malaria or chronic cardiovascular conditions.
Breastfeeding is an obligatory requirement of mammalian survival. This process is associated with the adaptation of maternal physiology including transformation of the mammary gland into a milk-secreting organ. How maternal immunity contributes to mammary gland remodeling and function remains largely unknown. Here, we show that maternal adaptive immunity plays a critical role in shaping lactogenesis. Specifically, physiological adaptation during pregnancy is associated with thymic involution and paradoxical enrichment in intraepithelial lymphocyte (IEL) precursors that no longer migrate to the gut, but instead preferentially accumulate within the mammary gland. Within this compartment, IEL precursors differentiate into T-bet-expressing unconventional CD8aa lymphocytes with a cytotoxic signature which accumulate within the mammary epithelium in an IL-15-dependent manner. Mammary IEL control milk production by favoring differentiation of both contractile and milk-secreting cells, thereby promoting offspring fitness. Altogether, this work uncovers a previously unappreciated contribution of the maternal adaptive immune system in organismal remodeling during pregnancy.
