Mucosal Immunity in Mycobacterial infections

More than a century after the identification of the tubercle bacillus and the first attempts at vaccination, tuberculosis (TB) still remains one of the world’s most serious infectious diseases. TB, caused by the bacterium Mycobacterium tuberculosis, is typically a disease of the lung, which serves both as port of entry and as the major site of disease manifestation. The currently used vaccine, BCG, is administered parenterally and induces a systemic immune response. However, it fails to protect against pulmonary TB, thereby raising the question whether vaccination targeting the mucosal immunity in the lungs could be favourable. The respiratory mucosal surfaces represent the first line of defence against a multitude of pathogens. Secretory IgA, in mucosal secretions has an important function by blocking entrance of pathogenic organisms and preventing infections. Additionally, a role for IgA in modulation of immune responses is currently being revealed. In this work, we investigated the relevance of mucosal IgA in protection against mycobacterial infections using mice deficient for IgA and the polymeric Ig receptor, the receptor responsible for mucosal secretions of IgA. Gene-targeted mice were more susceptible to mycobacterial infections in the respiratory tract and displayed reduced production of proinflammatory, and protective, factors such as IFN-γ and TNF-α in the lungs. The mechanisms explaining the defective proinflammatory responses in the lungs of deficient mice might involve impaired signalling through Fcα receptors, or homologous receptors, which could lead to inadequate activation of pulmonary macrophages. This could subsequently result in suboptimal induction and production of cytokines and chemokines important for attraction and migration of immune cells to the site of infection. Induction of optimal adaptive immune responses to combat mycobacterial infections requires prompt innate immune activation. Toll-like receptors (TLRs) are vital components of the innate branch of the immune system, ensuring early recognition of invading pathogens. Using TLR-deficient mice we demonstrated an important role for TLR2, and partly TLR4, in protection against mycobacterial infection in the respiratory tract. TLR2-deficient mice failed to induce proper proinflammatory responses at the site of infection, and macrophages derived from the knockout mice displayed impaired anti-mycobacterial activity. Experimental evidence has concluded that the immune response upon an infection can influence the outcome of succeeding infections with other pathogens. Concurrent infections might additionally interfere with responses to vaccinations and have deleterious effects. We developed an in vitro model to study the effect of a malaria infection on a successive M. tuberculosis infection. Our results demonstrate that a malaria blood-stage infection enhances the innate immune response to a subsequent M. tuberculosis infection with a Th1 prone profile. Reduced infectivity of malaria-exposed dendritic cells implies that a malaria infection could impose relative resistance to ensuing M. tuberculosis infection. However, a prolonged Th1 response may interfere with malaria parasite control. The outcome of this work emphasizes the importance of generating effective immune responses in the local mucosal environment upon respiratory mycobacterial infections. It furthermore puts new light on the immunological interaction between parasites and mycobacteria, which could have implications for future vaccine research

Does IgA play a role in protection against pulmonary tuberculosis?

More than a century after the identification of the tubercle bacillus and the first attempts at vaccination, tuberculosis (TB) still remains one of the world’s most serious infectious diseases. TB is typically a disease of the lung, which serves both as port of entry and as the major site of disease manifestation. The currently used vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is administered parentally and induces a systemic immune response. However, it fails to protect against pulmonary TB, thereby raising the question whether vaccination targeting the mucosal immunity in the lungs could be favourable. The respiratory mucosal surfaces represent the first line of defence against a multitude of pathogens. Secretory IgA (sIgA) in mucosal secretions has an important function by blocking entrance of pathogenic organisms and preventing infections. Yet, another role for IgA in protection against intracellular pathogens has lately been appreciated, when sIgA was demonstrated to neutralize viruses intracellulary. We aimed to investigate the relevance of sIgA in protection against mycobacterial infections using mice deficient for IgA and the polymeric Ig receptor. Mice were immunized intranasally with a mycobacterial antigen which elicited, in wild-type mice, a strong IgA response in mucosal secretions in the respiratory tract. Gene-targeted mice failed to induce the same response and more importantly, were more susceptible to mycobacterial infections in the respiratory tract, as demonstrated by higher bacterial loads in the lungs than wild-type mice. Analysis of immune responses after infection revealed reduced production of proinflammatory, and protective, factors such as IFN-γ and TNF-α in the lungs of deficient mice, which was in concordance with the higher bacterial burden seen in the lungs of these mice. The mechanisms explaining the defective proinflammatory responses in the lungs of deficient mice are not clear but might involve impaired signalling through Fcα receptors, or homologous receptors, which could lead to inadequate activation of pulmonary macrophages. This could subsequently result in suboptimal induction and production of cytokines and chemokines important for attraction and migration of cells to sites of infection in the lungs. Our results demonstrate a role for IgA in protection against mycobacterial infection in the respiratory tract by blocking the entrance of the mycobacterium into the lungs, and/or by modulating the locally induced proinflammatory immune responses

On the Tissue-type Plasminogen Activator (t-PA) -7,351C>T Enhancer Polymorphism. Importance for endothelial t-PA gene expression and arterial thrombotic disease

Local endothelial release of tissue-type plasminogen activator (t-PA) is an important thromboprotective mechanism. Earlier work by our group has identified a common single nucleotide polymorphism (SNP) at the t-PA locus (-7,351C>T), located within a GC-box in the retinoic acid (RA) and steroid hormone responsive t-PA enhancer. This SNP was associated with local t-PA release in vivo, as subjects homozygous for the wild-type -7,351C allele had twice the t-PA release rates compared to carriers of the mutant T allele. The aim of the present thesis was to elucidate the physiological and pathophysiological relevance of this t-PA variant. TaqMan genotyping assays were designed for a set of SNPs in hemostatic genes to facilitate association studies on these SNPs and thrombotic disease. Specificity and reproducibility was confirmed by DNA sequencing and repeated genotyping. The pathophysiologial relevance of the t-PA -7,351C>T SNP was initially addressed in a prospective study on myocardial infarction (MI) in northern Sweden. An independent association for the t-PA -7,351C>T SNP was found, with a greater risk of MI in T allele carriers. In a large case-control study on ischemic stroke from western Sweden we did, however, not detect a similar association. This study also included a genetic variant of the main inhibitor of t-PA, the plasminogen activator inhibitor type-1 (PAI-1) -675 4G>5G SNP. A reduced risk of ischemic stroke was observed for the combined t-PA CC and PAI-1 4G4G genotype.In vitro studies were performed to functionally characterize the t-PA -7,351C>T SNP. Gel shift analysis using nuclear extracts derived form various cell types, including endothelial cells (ECs) and neuronal-like cells, revealed a strongly reduced binding affinity of transcription factors Sp1 and Sp3 to the T allele, which is interesting in view of the role for Sp1 in gene regulation and enhancer action. Transient transfections demonstrated a lower transcriptional activity in the T enhancer variant after stimulation with RA. An interaction between Sp1 and the RA receptor was also observed. ECs carrying the T allele showed a reduced t-PA induction, both at the mRNA and protein level, in response to RA and protein kinase C (PKC) activation. The combination of RA and PKC activation produced a synergistic t-PA response, resulting in a 2-fold difference in t-PA expression between genotypes.In conclusion, the t-PA -7,351C>T SNP affects endothelial t-PA gene expression at the level of transcription. The reduced expression seen with the mutant T allele may explain our finding of an increased risk for MI in individuals carrying this allele. The t-PA -7,351C>T SNP did not show a significant association to ischemic stroke, but a reduced risk was observed in subjects with the combined t-PA CC and PAI-1 4G4G genotype, supporting a differentiated and more complex role for t-PA and PAI-1 in the brain as compared to the heart

Species-specific regulation of t-PA and PAI-1 gene expression in human and rat astrocytes

In recent years, the role and physiological regulation of the serine protease tissue-type plasminogen activator (t-PA and its inhibitors, including plasminogen activator inhibitor type-1 (PAI-1, in the brain have received much attention. However, as studies focusing these issues are difficult to perform in humans, a great majority of the studies conducted to date have utilized rodent in vivo and/or in vitro models. In view of the species-specific structural differences present in both the t-PA and the PAI-1 promoters, we have compared the response of these genes in astrocytes of rat and human origin. We reveal marked quantitative and qualitative species-specific differences in gene induction following treatment with various physiological and pathological stimuli. Thus, our findings are of importance for the interpretation of previous and future results related to t-PA and PAI-1 expression

Nail psoriasis dynamics during biologic treatment and withdrawal in patients with psoriasis who may be at high risk of developing psoriatic arthritis: a post hoc analysis of the VOYAGE 2 randomized trial

Abstract Background Nail psoriasis is a common, physiologically, and psychologically disruptive, and yet often under-treated manifestation of psoriasis. The objectives of this analysis were to investigate the trajectory of nail psoriasis, a risk factor for psoriatic arthritis (PsA), with guselkumab vs adalimumab treatment followed by withdrawal, and determine characteristics associated with nail response in patients treated with guselkumab. Methods This post hoc analysis of the phase III trial VOYAGE 2 included patients with moderate-to-severe plaque psoriasis and baseline nail involvement. Nail Psoriasis Severity Index (NAPSI) and Psoriasis Area and Severity Index (PASI) were analyzed through week 48 in patients randomized to guselkumab or adalimumab. Multiple logistic regression analyzed factors associated with NAPSI 0/1 at week 24/week 48 following guselkumab treatment. In a separate analysis, patients were stratified by prior biologic experience. Results Overall, 272 vs 132 patients receiving guselkumab vs adalimumab had nail psoriasis at baseline. Lower baseline NAPSI and week 16 PASI were associated with achieving NAPSI 0/1 at week 24 (NAPSI, odds ratio 0.685 [95% confidence interval: 0.586, 0.802]; week 16 PASI, 0.469 [0.281, 0.782]) and week 48 (NAPSI, 0.784 [0.674, 0.914]; week 16 PASI, 0.557 [0.331, 0.937]) with guselkumab. Previous biologic experience did not impact NAPSI response. Following treatment withdrawal at week 28, mean NAPSI was maintained in the guselkumab arm (week 24 1.7, week 48 1.9) and increased slightly in the adalimumab arm (week 24 1.4, week 48 2.3). Mean PASI increased across both treatment arms. Conclusions Higher skin efficacy at week 16 was associated with better nail responses during guselkumab treatment. Nail psoriasis improvements reflected skin improvements. Following guselkumab withdrawal, nail response was maintained longer than skin response. Future studies should investigate whether such improvements in nail response reduce patients’ risk of later PsA development. Trial registration ClinicalTrials.gov, NCT02207244. Registered July 31, 2014

Odds ratios and 95% confidence intervals for the associations between SNPs in <i>BDNF</i> and poor functional outcome after stroke as measured by mRS ≧2 at 3 months (A), 2 years (B), and 7 years (C) post-stroke.

<p>White boxes, adjusted for age and sex; grey boxes adjusted for age, sex, smoking, diabetes, hypertension, hyperlipidemia, TOAST subtype and NIHSS during the acute phase. † <i>P</i><0.01 compared with good outcome after stroke. Patients that died after the 2-year follow-up were excluded from the 7-year analyses (n = 73).</p