Publications

Clostridium perfringens strains produce severe diseases, including myonecrosis and enteritis necroticans, in humans and animals. Diseases are mediated by the production of potent toxins that often damage the site of infection, e.g., skin epithelium during myonecrosis. In planktonic cultures, the regulation of important toxins, such as CPA, CPB, and PFO, is controlled by the C. perfringens Agr-like (CpAL) quorum sensing (QS) system. Strains also encode a functional LuxS/AI-2 system. Although C. perfringens strains form biofilm-like structures, the regulation of biofilm formation is poorly understood. Therefore, our studies investigated the role of CpAL and LuxS/AI-2 QS systems and of QS-regulated factors in controlling the formation of biofilms. We first demonstrate that biofilm production by reference strains differs depending on the culture medium. Increased biomass correlated with the presence of extracellular DNA in the supernatant, which was released by lysis of a fraction of the biofilm population and planktonic cells. Whereas ΔagrB mutant strains were not able to produce biofilms, a ΔluxS mutant produced wild-type levels. The transcript levels of CpAL-regulated cpa and pfoA genes, but not cpb, were upregulated in biofilms compared to planktonic cultures. Accordingly, Δcpa and ΔpfoA mutants, in type A (S13) or type C (CN3685) backgrounds, were unable to produce biofilms, whereas CN3685Δcpb made wild-type levels. Biofilm formation was restored in complemented Δcpa/cpa and ΔpfoA/pfoA strains. Confocal microscopy studies further detected CPA partially colocalizing with eDNA on the biofilm structure. Thus, CpAL regulates biofilm formation in C. perfringens by increasing levels of certain toxins required to build biofilms.

BACKGROUND

Anemia is common in chronic kidney disease (CKD) and associated with poor outcomes. In cross-sectional studies, lower estimated glomerular filtration rate (eGFR) has been associated with increased risk for anemia. The aim of this study was to determine how hematocrit changes as eGFR declines and what factors impact this longitudinal association.

METHODS

We followed 1094 African-Americans with hypertensive nephropathy who participated in the African-American Study of Kidney Disease and Hypertension. Mixed effects models were used to determine longitudinal change in hematocrit as a function of eGFR. Interaction terms were used to assess for differential effects of age, gender, baseline eGFR, baseline proteinuria, malnutrition and inflammation on eGFR-associated declines in hematocrit. In sensitivity analyses, models were run using iGFR (by renal clearance of I(125) iothalamate) in place of eGFR.

RESULTS

At baseline, mean hematocrit was 39% and 441 (40%) individuals had anemia. The longitudinal relationship between eGFR and hematocrit differed by baseline eGFR and was steeper when baseline eGFR was <45 mL/min/1.73 m(2). For example, the absolute decline in hematocrit per 10 mL/min/1.73 m(2) decline in longitudinal eGFR was -3.7, -1.3 and -0.5% for baseline eGFR values of 20, 40 and 60 mL/min/1.73 m(2), respectively (P < 0.001 comparing the longitudinal association between baseline eGFR = 40 or 60 versus baseline eGFR = 20 mL/min/1.73 m(2)). Similarly, male sex, younger age (<65 years) and higher baseline proteinuria (protein-to-creatinine ratio >0.22) were associated with greater hematocrit declines per unit decrease in longitudinal eGFR compared with female sex, older age and low baseline proteinuria, respectively (P-interaction <0.05 for each comparison). The longitudinal eGFR-hematocrit association did not differ by body mass index, serum albumin or C-reactive protein.

CONCLUSIONS

Men, younger individuals and those with low baseline eGFR (<45 mL/min/1.73 m(2)) or baseline proteinuria are particularly at risk for eGFR-related declines in hematocrit.

Gastrointestinal T lymphocytes are critical for mucosal immunity and HIV pathogenesis, yet little is known about normal T cell numbers and phenotypes in different regions of the gut, or the degree to which ART can restore levels to those of HIV-uninfected individuals. To investigate these questions, we measured T cell frequencies and markers of memory, activation, anergy, and homing in the blood, ileum, and rectum of HIV- and ART-suppressed HIV+ adults. In HIV- individuals, T cell frequencies and phenotypes differed significantly between sites. Compared to HIV- adults, HIV+ adults had lower absolute CD4+T cell counts in the ileal lamina propria and lower relative CD4+T cell counts in the blood and ileum. In the gut, HIV+ adults had a higher proportion of CD38+ CD4+T cells, a lower proportion of terminally-differentiated effector cells, and, in the rectum, a higher proportion of CTLA-4+ CD4+T cells. In HIV+ individuals, relative CD4+T cell numbers in the ileum correlated with the proportion of CTLA-4+ CD4+T cells, whereas in the rectum, they tended to correlate with the proportion of circulating CD4+T cells expressing α4β7 or CCR6. Mechanisms of T cell reconstitution may differ throughout the gut, with homing contributing more in the rectum while ileal reconstitution is associated with mucosal CD4+T cell anergy.