Return to CAP Home
Printable Version

  Clinical Abstracts

title

 

 

 

cap today

May 2002

Hepatitis C virus inhibition of T-lymphocyte response
Hepatitis C infection is a serious and growing public health problem, with approximately 4 million cases in the United States alone. Hepatitis C virus evades effective immune recognition and shows an extremely high rate of viral persistence in the infected individual—more than 90 percent, versus 10 percent for hepatitis B. The typical subclinical phase may last 10 to 20 years, after which HCV infection may progress to end-stage liver disease and is also highly correlated with the development of hepatocellular carcinoma and autoimmune disease. An intrinsically high rate of mutation in the RNA genome of HCV and variability in the envelope protein likely contribute to the ineffective antibody response against the virus. T-lymphocyte responses to HCV gene products have been demonstrated, but the role of these responses in controlling the infection are not well defined. HCV replication persists in hepatocytes of patients with the infection, although lymphocytic infiltration is detectable in the livers of these patients. Lack of an animal model had been a major difficulty in addressing the mechanism of viral persistence and viral replication with respect to host immune responses in HCV. The authors developed a murine model to examine the influence of specific HCV proteins on viral-antigen recognition and viral clearance. In this way, they demonstrated that expression of HCV structural or nonstructural proteins using recombinant vaccinia or Sindbis virus resulted in vigorous T-lymphocyte responses and nonlethal infections with rapid viral clearance. On the other hand, hepatitis C core protein suppresses protective immune responses, such as the antiviral cytotoxic T-lymphocyte response. This immunomodulatory role of core protein may play a critical role in the pathogenesis of hepatitis C viral infection in conjunction with identifying circulating naked core protein in the plasma of those infected with HCV. The authors have screened a human leukocyte cDNA library using a yeast two-hybrid system to identify host proteins with which core can interact. One-quarter of the clones identified encoded the p33gC1q receptor specific for the globular heads of the complement C1q protein. In the current study, the authors described the identification of the core binding to the gC1qR and have undertaken a comprehensive analysis of the interaction as well as the effect of the core on T-cell responsiveness. Like C1q, HCV core can inhibit T-cell proliferative responses in vitro. This HCV core-induced anti-T-cell proliferation is reversed by adding anti-gC1qR antibody in a T-cell proliferation assay. Furthermore, the authors determined that HCV core binds the region spanning amino acids 188 to 259 of gC1qR, which is a site distinct from the binding region of C1q.

Kittlesen DJ, Chianese-Bullock KA, Yao ZQ, et al. Interaction between complement receptor gC1qR and hepatitis C virus core protein inhibits T-lymphocyte proliferation. J Clin Invest. 2000;106:1239-1249.

Reprints: Young S. Hahn, Box 801386, University of Virginia Health Sciences Center, Charlottesville, VA 22908; ysh5E@virginia.edu

Use of fractalkine and its receptor in cardiac allograft rejection
Acute allograft rejection is characterized by a vigorous cellular immune response with an influx of circulating leukocytes into the transplant. Activated immune cells accumulate in the allograft, which is essential to the pathogenesis of tissue injury. Recruiting leukocytes into sites of inflammation involves a tightly regulated series of molecular interactions that includes capture and rolling of cells mediated by selectins followed by fixation on the endothelium, which is a process mediated by the integrins. During these events, the leukocytes become activated through stimulation of G protein-coupled chemokine receptors, resulting in enhanced integrin adhesiveness and activation-dependent stable arrest. The recruitment process culminates in diapedesis across the endothelium and migration into the inflamed tissue. In rejection, the expression of various adhesion molecules, such as ICAM-1 and E-selectin, are up-regulated, but the functional importance of this has not been well established. Although an expression of a variety of chemokines has been demonstrated in rejecting transplants, their contribution to the pathogenesis of rejection is not clear. The human chemokine fractalkine (FKN) and its murine homologue neurotactin recently have been identified as novel chemokines with unique transmembrane chemokine/mucin hybrid structures. FKN promotes leukocyte activation and, unlike other chemokines, can mediate each step of the leukocyte adhesion cascade. FKN interacts with its unique receptor, CX3CR1, to affect firm adhesion of resting monocytes, resting and activated CD8+ T lymphocytes, and activated NK cells. The authors postulated that FKN may play a functional role in allograft rejection and tested this hypothesis using mouse models. They demonstrated that FKN expression is enhanced in rejecting mouse cardiac allografts and that enhanced FKN expression on activated mouse endothelial cells promotes increased leukocyte adhesion. They also found that inhibition of FKN-CX3CR1 signaling with an anti-CX3CR1 Ab significantly prolongs survival of the cardiac allografts in mice. At early time points, the FKN expression was particularly prominent on the endothelium and vascular tissues. As rejection progressed, FKN expression was increased, with prominent anti-FKN staining seen around vessels and on cardiac myocytes. To determine the capacity of FKN on endothelial cells to promote leukocyte adhesion, the authors performed adhesion assays with PBMC and monolayers of TNF-a activated murine endothelial cells under low shear conditions. They found the treatment with anti-FKN or anti-CX3CR1-blocking Ab significantly inhibited PBMC binding, indicating that a large proportion of leukocyte binding to murine endothelium occurs via these receptors. Treatment of murine cardiac allograft recipients with daily injections of anti-CX3CR1 Ab significantly prolonged allograft survival from 7±1 to 49±30 days, which was highly significant. These studies identify a critical role for FKN in the pathogenesis of acute rejection and suggest that FKN may be a useful therapeutic target in rejection.

Robinson LA, Nataraj C, Thomas DW, et al. A role for fractalkine and its receptor (CX3CR1) in cardiac allograft rejection. J Immunol. 2000; 165:6067-6072.

Reprints: Dr. Lisa A. Robinson, Box 3959, Duke University Medical Center, Durham, NC 27710; robin025@mc.duke.edu

Biofilms in the urinary tract
A biofilm is a surface accumulation of microorganisms in which large amounts of organic polymers of microbial origin bind the cells and other material together and to the substratum. The bacteria growing in biofilms differ from planktonic cells in the same environment and from cells grown in pure laboratory cultures. The formation of a biofilm may be a stress response of bacteria to promote survival in a hostile environment. Killing doses of antibiotics determined in the laboratory may be ineffective in treating biofilms. The author reviewed the role of exopolysaccharides in producing a variety of extracellular polymers differing by organism and site. He asserted that fluoroquinolone at high concentrations—20 times the minimal inhibitory concentration—shows considerable killing effect against biofilms, but no commercially available drugs are sufficiently active against the cells in a mature biofilm. The author recommended treating urinary biofilm infection by managing the local urinary condition and removing the local underlying disease, as well as instituting a combination therapy of fluoroquinolone and macrolide or fluoroquinolone and fosfomycin.

Kumon H. Management of biofilm infections in the urinary tract. World J Surg. 2000;24:1193-1196.

Reprints: Dr. H. Kumon, Dept. of Urology, Okayama University Medical School, 2-5-1 Shikata, Okayama 700-8558, Japan; kumon@med.koayama-u.ac.jp

Hepatitis B vaccination and positive tests for hepatitis B surface antigen
Several reports have indicated that otherwise healthy individuals who have received hepatitis B vaccines may test positive for the HBV surface antigen for a short time after vaccination. The authors investigated HBsAg reactivity in eight healthy volunteers after they received their first dose of HBV vaccine. Blood samples were collected on days 0, 3, 5, 7, and 10 post-vaccination. Several different screening assays were used. The highest reactivities were found on samples taken on day 3, but two of the eight volunteers were reactive on day 5. All samples from days 7 and 10 were nonreactive. This study demonstrated that HBsAg assays detect individuals who have recently received the HBV vaccine up to five days after vaccination. Blood donors who have received the HBV vaccine probably should be deferred from blood donation for seven days after being vaccinated.

Dow BC, Yates P, Galea G, et al. Hepatitis B vaccines may be mistaken for confirmed hepatitis B surface antigen-positive blood donors. Vox Sang. 2002;82:15-17.

Correspondence: Dr. Brian C. Dow, SNBTS Microbiology Reference Unit, West of Scotland Transfusion Centre, 25 Shelley Rd., Glasgow G12 OXB, United Kingdom; brian.dow@snbts.csa.scot.nhs.uk

C. pneumoniae infection and mortality from ischemic heart disease
Several small retrospective studies have linked ischemic heart disease with various chronic infections, in particular those caused by Helicobacter pylori and Chlamydia pneumoniae. The susceptibility of these studies to bias and confounding have led to interest in designing and conducting large, prospective studies of socially homogeneous cohorts of subjects. (Socioeconomically disadvantaged individuals may be more likely to develop infection and coronary artery disease independently of one another.) Previous studies have generated mixed results, regardless of whether IgG or IgA was measured. The authors undertook a study to determine the concentration of IgG and IgA antibodies to C. pneumoniae in a cohort of 21,520 healthy British professional men aged 35 to 64 years who went to the BUPA center in London for routine medical examinations between 1975 and 1982. The distributions of concentrations of IgG and IgA antibodies to C. pneumoniae were similar in the 647 men who subsequently died of ischemic heart disease and the 1,294 age-matched controls who did not die. There was no association with heart disease at any cut-off point chosen to define seropositivity.

Wald NJ, Law MR, Morris JK, et al. Chlamydia pneumoniae infection and mortality from ischaemic heart disease: large prospective study. Brit Med J. 2000;321:204-207.

Reprints: N.J. Wald, BUPA Epidemiological Research Group, Wolfson Institute of Preventive Medicine, St. Bartholomew’s and The Royal London School of Medicine and Dentistry, London, EC1M 6BQ, England; n.j.wald@mds.qmw.ac.uk

The ABCA1 gene and Tangier disease
Low high-density lipoprotein cholesterol level is an independent risk factor for coronary artery disease. Inherited forms of this condition include Tangier disease and familial hypoalphalipoproteinemia associated with reduced cholesterol efflux. The authors and others have shown that FHA is allelic to Tangier disease and due to heterozygosity for mutations of the ABCA1 gene. They reported having identified 13 ABCA1 mutations in 11 families and have examined the phenotypes of 77 individuals heterozygous for mutations in the ABCA1 gene. ABCA1 heterozygotes have significantly reduced HDL cholesterol and significantly elevated triglycerides. Age is an important effect modifier of the carrier state, with a greater proportion of individuals 30 to 70 years of age having HDL-C greater than the fifth percentile for age and gender, compared with carriers younger than 30 years old. These ABCA1 heterozygotes have a greater than three-fold increased risk of CAD and earlier onset than unaffected family members. CAD correlates with the level of cholesterol efflux, which correlates directly with HDL-C levels. This provides direct evidence that impaired cholesterol efflux and, consequently, reverse cholesterol transport are associated with reduced plasma HDL-C levels and increased risk of CAD.

Clee SM, Kastelein JJ, vanDam M, et al. Age and residual cholesterol efflux affect HDL cholesterol levels and coronary artery disease in ABCA1 heterozygotes. J Clin Invest. 2000;106(10):1263-1270.

Reprints: Michael R. Hayden, Centre for Molecular Medicine and Therapeutics, 980 W. 29th Ave., Vancouver, BC, Canada, V5H 4Z4; mrh@cmmt.ubc.ca

Lack of diurnal variation in C-reactive protein
Baseline high-sensitivity C-reactive protein has been shown to be a powerful independent predictor of cardiovascular risk. CRP is produced in the liver in response to stimulation by interleukin-6 and other cytokines. The plasma concentration of IL-6 has been shown to follow a marked diurnal variation—low in the morning and high in the evening. This variation may reflect feedback inhibition of cytokine concentration by endogenous cortisol. The authors conducted a study to assess whether such diurnal variation in CRP levels in healthy subjects could be detected using a new high-sensitivity assay. They sampled blood from 20 healthy male and three healthy female subjects aged 21 to 35 years. The samples were taken hourly during a baseline day in a controlled environment (eight hours of nighttime sleep). Only three of the subjects had CRP concentrations greater than 2 mg/L. The raw measurements were stable throughout the 24 hours. When interpreted by comparison with population-based quintiles, no subject was reclassified as a result of diurnal variation. Nonparametric ANOVA and cosine curve fitting of the data were negative for diurnal variation.

Meier-Ewert HK, Ridker PM, Rifai N, et al. Absence of diurnal variation of C-reactive protein concentrations in healthy human subjects. Clin Chem. 2001;47:426-430.

Reprints: Hans K. Meier-Ewert, Dept. of Cardiology, Lahey Clinic Medical Center, 41 Mall Rd., Burlington, MA 01805; hans.k.meierewert@lahey.org

Diagnosis of Lyme disease in children
Overdiagnosis and overtreatment are potential problems of Lyme disease, the most common vector-borne disease in the United States. In 1995, the Centers for Disease Control and Prevention provided criteria for diagnosing Lyme disease. The authors examined the incidence of overdiagnosis of Lyme disease in an endemic area using the diagnostic criteria developed by the CDC. The CDC criteria require the presence of erythema migrans or characteristic symptoms of active Lyme disease (articular, neurologic, or cardiac manifestations) with serologic confirmation. Serologic confirmation involved a two-test approach and included an enzyme immunoassay or an immunofluorescent assay and a Western immunoblot for IgG and IgM antibody. The authors studied 216 patients with presumptive Lyme disease who were referred to a pediatric infectious disease clinic. Thirty-nine children had previously been diagnosed with and treated for Lyme disease, and 17 had symptoms of another illness but were thought to have an acute recurrence of Lyme disease by the referring physician or family member. One hundred and nine of the subjects did not meet the diagnostic criteria for Lyme disease. Of the 216 children, 68 met the criteria for active Lyme disease (36 had arthritis, 15 had erythema migrans, and 17 had central nervous system disease—two had Lyme meningitis and 15 had facial nerve palsy). One hundred and forty-seven of the 216 children had a history of tick bite but never had symptoms, and all had received antibiotic therapy. The authors concluded that overdiagnosis and overtreatment of Lyme disease in children is common and is significantly related to lack of education about diagnostic guidelines and misinterpretation of Western immunoblot results.

Qureshi MZ, New D, Zulqarni NJ, et al. Overdiagnosis and overtreatment of Lyme disease in children. Pediatr Infect Dis J. 2002;21:12-14.

Correspondence: Department of Pediatrics, Division of Infectious Diseases, State University of New York at Stony Brook, Stony Brook, NY 11794 (reprints not available)

Prenatal CMV diagnosis
Cytomegalovirus infection occurs intrauterinely in 0.3 to 2.0 percent of all live births, making it the most common intrauterine infection. Only 10 to 15 percent of infected fetuses show symptoms at birth, but severe central nervous system and multi-organ involvement may lead to a 20 to 30 percent perinatal mortality rate in this group and major neurologic sequelae in more than 90 percent of survivors. The authors assessed whether amniotic CMV viral load determinations correlate with outcome. They studied 138 pregnant women with primary infection, defined as IgG seroconversion or presence of IgM with low avidity IgG. Of these subjects, 68 accepted amniocentesis. Amniotic fluid samples were tested by polymerase chain-reaction and quantitative PCR. CMV infection in neonates was determined by urinary viral isolation during the first postnatal week or histologically in aborted fetuses. CMV infection was found in 16 fetuses and neonates (23 percent)—five of whom were symptomatic. Quantitative PCR showed that 103 genome equivalents or greater predicted mother-child infection with 100 percent probability and 105 genome equivalents or greater predicted development of a symptomatic infection. The authors concluded that fewer CMV-infected fetuses are at risk for CMV disease than expected.

Guerra B, Lazzarotto T, Quarta S, et al. Prenatal diagnosis of symptomatic congenital cytomegalovirus infection. Am J Obstet Gynecol. 2000;183(2):476-482.

Reprints: Dr. Brunella Guerra, Clinica Obstetrica e Ginecologica II, Policlinico S. Orsola, Via Massarenti 13, 40138 Bologna, Italy.

Incidence of tuberculosis in U.S. immigrants
Infection with Mycobacterium tuberculosis is extremely widespread internationally, affecting as much as one-third of the worlds population. In developed countries, substantial immigration rates have contributed to the incidence of TB and sustained TB occurrence rates. The number of cases of TB in the United States has decreased since its peak in 1992, but the decline has occurred among those born in the United States. The authors performed a descriptive analysis of U.S. TB surveillance data between 1993 and 1998 and found that TB among the U.S. foreign-born population increased 2.6 percent, totalling 7,402 in 1993 and 7,591 in 1998, and the proportion of all U.S. TB cases represented by foreign-born persons rose from 29.8 percent to 41.6 percent. The 1993 to 1998 TB case rate was 32.9 per 100,000 foreign-born persons and 5.8 per 100,000 U.S.-born persons. Of cases involving foreign-born subjects, 73.4 percent were reported in the states of California, New York, Texas, Florida, New Jersey, and Illinois, and two-thirds of the infected subjects originally were from Mexico, Philippines, Vietnam, India, China, Haiti, or South Korea. Most subjects with TB were males aged 25 to 44 years—51.5 percent had been in the United States less than five years before diagnosis. The authors concluded that TB control strategies for the foreign-born community are essential to eliminating the disease in the United States.

Talbot EA, Moore M, McCray E, et al. Tuberculosis among foreign-born persons in the United States, 1993-1998. JAMA. 2000;284:2894-2900.

Reprints: Dr. Marisa Moore, Surveillance and Epidemiology Branch, Division of TB Elimination, Centers for Disease Control and Prevention, Mail Stop E-10, Atlanta, GA 30333; mmoore@cdc.gov