Poly-N-Acetylglucosamine Expression by Wild-Type Yersinia pestis Is Maximal at Mammalian, Not Flea, Temperatures

Numerous bacteria, including Yersinia pestis, express the poly-N-acetylglucosamine (PNAG) surface carbohydrate, a major component of biofilms often associated with a specific appearance of colonies on Congo red agar. Biofilm formation and PNAG synthesis by Y. pestis have been reported to be maximal at 21 to 28°C or “flea temperatures,” facilitating the regurgitation of Y. pestis into a mammalian host during feeding, but production is diminished at 37°C and thus presumed to be decreased during mammalian infection. Most studies of PNAG expression and biofilm formation by Y. pestis have used a low-virulence derivative of strain KIM, designated KIM6+, that lacks the pCD1 virulence plasmid, and an isogenic mutant without the pigmentation locus, which contains the hemin storage genes that encode PNAG biosynthetic proteins. Using confocal microscopy, fluorescence-activated cell sorter analysis and growth on Congo red agar, we confirmed prior findings regarding PNAG production with the KIM6+ strain. However, we found that fully virulent wild-type (WT) strains KIM and CO92 had maximal PNAG expression at 37°C, with lower PNAG production at 28°C both in broth medium and on Congo red agar plates. Notably, the typical dark colony morphology appearing on Congo red agar was maintained at 28°C, indicating that this phenotype is not associated with PNAG expression in WT Y. pestis. Extracts of WT sylvatic Y. pestis strains from the Russian Federation confirmed the maximal expression of PNAG at 37°C. PNAG production by WT Y. pestis is maximal at mammalian and not insect vector temperatures, suggesting that this factor may have a role during mammalian infection

Apoptosis of αβ T lymphocytes in the nervous system in experimental autoimmune encephalomyelitis: Its possible implications for recovery and acquired tolerance

We have recently shown that apoptosis, an active process of cellular self-destruction, occurs in the central nervous system in Lewis rats with acute experimental autoimmune encephalomyelitis (EAE) induced by inoculation with myelin basic protein (MBP) and adjuvants. Conventional light and electron microscopic studies suggested that some of the apoptotic cells were oligodendrocytes and that others were hematogenous mononuclear cells. To determine whether any of the apoptotic cells were T lymphocytes, we used the technique of pre-embedding immunolabelling which allows sufficient preservation of the ultrastructure to permit recognition of apoptotic changes while at the same time preserving surface antigens so that the identity of the apoptotic cells can be determined by immunocytochemistry. Light microscopic immunocytochemistry using the mono-clonal antibodies OX-34 (CD2) and R73 (alpha beta T-cell receptor) revealed that 10% of the CD2+ cells and 5% of the alpha beta T lymphocytes in the parenchyma of the spinal cord were dying by apoptosis. The presence of apoptotic alpha beta T cells was confirmed by electron microscopy. About half of all the apoptotic cells within the spinal cord were labelled by these antibodies. It is possible that some of the unlabelled apoptotic cells were also T lymphocytes but that others were glial cells such as oligodendrocytes. One possible interpretation of this T-cell apoptosis is that it represents activation-induced cell death, which has recently been shown to provide a mechanism of clonal elimination of mature as well as immature autoreactive T cells. Another possible interpretation is that it is a result of corticosterone released during the course of EAE. The apoptotic elimination of target-antigen-specific lymphocytes within the target organ in this autoimmune disease may contribute to the subsidence of inflammation and, if ongoing, to the development of tolerance

Antibody-mediated enhancement of community-acquired methicillin-resistant Staphylococcus aureus infection

Community-acquired infections caused by methicillin-resistant Staphylococcus aureus (MRSA) expressing the Panton-Valentine leukocidin (PVL) are rampant, but the contribution of PVL to bacterial virulence remains controversial. While PVL is usually viewed as a cytotoxin, at sublytic amounts it activates protective innate immune responses. A leukotoxic effect might predominate in high inoculum studies, whereas protective proinflammatory properties might predominate in settings with lower bacterial inocula that more closely mimic what initially occurs in humans. However, these protective effects might possibly be neutralized by antibodies to PVL, which are found in normal human sera and at increased levels following PVL+ S. aureus infections. In a low-inoculum murine skin abscess model including a foreign body at the infection site, strains deleted for the pvl genes replicated more efficiently within abscesses than isogenic PVL+ strains. Coinfection of mice at separate sites with isogenic PVL+ and PVL- MRSA abrogated the differences in bacterial burdens, indicating a systemic effect on host innate immunity from production of PVL. Mice given antibody to PVL and then infected with seven different PVL+ strains also had significantly higher bacterial counts in abscesses compared with mice given nonimmune serum. Antibody to PVL had no effect on MRSA strains that did not produce PVL. In vitro, antibody to PVL incapacitated PVL-mediated activation of PMNs, indicating that virulence of PVL+ MRSA is enhanced by the interference of PVL-activated innate immune responses. Given the high rates of primary and recurring MRSA infections in humans, it appears that antibodies to PVL might contribute to host susceptibility to infection

Titration of medications and outcomes in multi-ethnic heart failure cohorts (with reduced ejection fraction) from Singapore and New Zealand

Aims: We investigated titration patterns of angiotensin-converting enzyme inhibitors (ACEis)/angiotensin receptor blockers (ARBs) and beta-blockers, quality of life (QoL) over 6 months, and associated 1 year outcome [all-cause mortality/heart failure (HF) hospitalization] in a real-world population with HF with reduced ejection fraction (HFrEF). Methods and results: Participants with HFrEF (left ventricular ejection fraction &lt;40%) from a prospective multi-centre study were examined for use and dose [relative to guideline-recommended maintenance dose (GRD)] of ACEis/ARBs and beta-blockers at baseline and 6 months. ‘Stay low’ was defined as &lt;50% GRD at both time points, ‘stay high’ as ≥50% GRD, and ‘up-titrate’ and ‘down-titrate’ as dose trajectories. Among 1110 patients (mean age 63 ± 13 years, 16% women, 26% New York Heart Association Class III/IV), 714 (64%) were multi-ethnic Asians from Singapore and 396 were from New Zealand (mainly European ethnicity). Baseline use of either ACEis/ARBs or beta-blockers was high (87%). Loop diuretic was prescribed in &gt;80% of patients, mineralocorticoid receptor antagonist in about half of patients, and statins in &gt;90% of patients. At baseline, only 11% and 9% received 100% GRD for each drug class, respectively, with about half (47%) achieving ≥50% GRD for ACEis/ARBs or beta-blockers. At 6 months, a large majority remained in the ‘stay low’ category, one third remained in ‘stay high’, whereas 10–16% up-titrated and 4–6% down-titrated. Patients with lower (vs. higher) N-terminal pro-beta-type natriuretic peptide levels were more likely to be up-titrated or be in ‘stay high’ for ACEis/ARBs and beta-blockers (P = 0.002). Ischaemic aetiology, prior HF hospitalization, and enrolment in Singapore (vs. New Zealand) were independently associated with higher odds of ‘staying low’ (all P &lt; 0.005) for prescribed doses of ACEis/ARBs and beta-blockers. Adjusted for inverse probability weighting, ≥100% GRD for ACEis/ARBs [hazard ratio (HR) = 0.42; 95% confidence interval (CI) 0.24–0.73] and ≥50% GRD for beta-blockers (HR = 0.58; 95% CI 0.37–0.90) (vs. Nil) were associated with lower hazards for 1 year composite outcome. Country of enrolment did not modify the associations of dose categories with 1 year composite outcome. Higher medication doses were associated with greater improvements in QoL. Conclusions: Although HF medication use at baseline was high, most patients did not have these medications up-titrated over 6 months. Multiple clinical factors were associated with changes in medication dosages. Further research is urgently needed to investigate the causes of lack of up-titration of HF therapy (and its frequency), which could inform strategies for timely up-titration of HF therapy based on clinical and biochemical parameters.</p

Titration of medications and outcomes in multi-ethnic heart failure cohorts (with reduced ejection fraction) from Singapore and New Zealand

Aims: We investigated titration patterns of angiotensin-converting enzyme inhibitors (ACEis)/angiotensin receptor blockers (ARBs) and beta-blockers, quality of life (QoL) over 6 months, and associated 1 year outcome [all-cause mortality/heart failure (HF) hospitalization] in a real-world population with HF with reduced ejection fraction (HFrEF). Methods and results: Participants with HFrEF (left ventricular ejection fraction &lt;40%) from a prospective multi-centre study were examined for use and dose [relative to guideline-recommended maintenance dose (GRD)] of ACEis/ARBs and beta-blockers at baseline and 6 months. ‘Stay low’ was defined as &lt;50% GRD at both time points, ‘stay high’ as ≥50% GRD, and ‘up-titrate’ and ‘down-titrate’ as dose trajectories. Among 1110 patients (mean age 63 ± 13 years, 16% women, 26% New York Heart Association Class III/IV), 714 (64%) were multi-ethnic Asians from Singapore and 396 were from New Zealand (mainly European ethnicity). Baseline use of either ACEis/ARBs or beta-blockers was high (87%). Loop diuretic was prescribed in &gt;80% of patients, mineralocorticoid receptor antagonist in about half of patients, and statins in &gt;90% of patients. At baseline, only 11% and 9% received 100% GRD for each drug class, respectively, with about half (47%) achieving ≥50% GRD for ACEis/ARBs or beta-blockers. At 6 months, a large majority remained in the ‘stay low’ category, one third remained in ‘stay high’, whereas 10–16% up-titrated and 4–6% down-titrated. Patients with lower (vs. higher) N-terminal pro-beta-type natriuretic peptide levels were more likely to be up-titrated or be in ‘stay high’ for ACEis/ARBs and beta-blockers (P = 0.002). Ischaemic aetiology, prior HF hospitalization, and enrolment in Singapore (vs. New Zealand) were independently associated with higher odds of ‘staying low’ (all P &lt; 0.005) for prescribed doses of ACEis/ARBs and beta-blockers. Adjusted for inverse probability weighting, ≥100% GRD for ACEis/ARBs [hazard ratio (HR) = 0.42; 95% confidence interval (CI) 0.24–0.73] and ≥50% GRD for beta-blockers (HR = 0.58; 95% CI 0.37–0.90) (vs. Nil) were associated with lower hazards for 1 year composite outcome. Country of enrolment did not modify the associations of dose categories with 1 year composite outcome. Higher medication doses were associated with greater improvements in QoL. Conclusions: Although HF medication use at baseline was high, most patients did not have these medications up-titrated over 6 months. Multiple clinical factors were associated with changes in medication dosages. Further research is urgently needed to investigate the causes of lack of up-titration of HF therapy (and its frequency), which could inform strategies for timely up-titration of HF therapy based on clinical and biochemical parameters.</p

Titration of medications and outcomes in multi-ethnic heart failure cohorts (with reduced ejection fraction) from Singapore and New Zealand

Aims: We investigated titration patterns of angiotensin-converting enzyme inhibitors (ACEis)/angiotensin receptor blockers (ARBs) and beta-blockers, quality of life (QoL) over 6 months, and associated 1 year outcome [all-cause mortality/heart failure (HF) hospitalization] in a real-world population with HF with reduced ejection fraction (HFrEF). Methods and results: Participants with HFrEF (left ventricular ejection fraction &lt;40%) from a prospective multi-centre study were examined for use and dose [relative to guideline-recommended maintenance dose (GRD)] of ACEis/ARBs and beta-blockers at baseline and 6 months. ‘Stay low’ was defined as &lt;50% GRD at both time points, ‘stay high’ as ≥50% GRD, and ‘up-titrate’ and ‘down-titrate’ as dose trajectories. Among 1110 patients (mean age 63 ± 13 years, 16% women, 26% New York Heart Association Class III/IV), 714 (64%) were multi-ethnic Asians from Singapore and 396 were from New Zealand (mainly European ethnicity). Baseline use of either ACEis/ARBs or beta-blockers was high (87%). Loop diuretic was prescribed in &gt;80% of patients, mineralocorticoid receptor antagonist in about half of patients, and statins in &gt;90% of patients. At baseline, only 11% and 9% received 100% GRD for each drug class, respectively, with about half (47%) achieving ≥50% GRD for ACEis/ARBs or beta-blockers. At 6 months, a large majority remained in the ‘stay low’ category, one third remained in ‘stay high’, whereas 10–16% up-titrated and 4–6% down-titrated. Patients with lower (vs. higher) N-terminal pro-beta-type natriuretic peptide levels were more likely to be up-titrated or be in ‘stay high’ for ACEis/ARBs and beta-blockers (P = 0.002). Ischaemic aetiology, prior HF hospitalization, and enrolment in Singapore (vs. New Zealand) were independently associated with higher odds of ‘staying low’ (all P &lt; 0.005) for prescribed doses of ACEis/ARBs and beta-blockers. Adjusted for inverse probability weighting, ≥100% GRD for ACEis/ARBs [hazard ratio (HR) = 0.42; 95% confidence interval (CI) 0.24–0.73] and ≥50% GRD for beta-blockers (HR = 0.58; 95% CI 0.37–0.90) (vs. Nil) were associated with lower hazards for 1 year composite outcome. Country of enrolment did not modify the associations of dose categories with 1 year composite outcome. Higher medication doses were associated with greater improvements in QoL. Conclusions: Although HF medication use at baseline was high, most patients did not have these medications up-titrated over 6 months. Multiple clinical factors were associated with changes in medication dosages. Further research is urgently needed to investigate the causes of lack of up-titration of HF therapy (and its frequency), which could inform strategies for timely up-titration of HF therapy based on clinical and biochemical parameters.</p