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Biomedical subjects

J A Barbara

Publications and source records attributed to J A Barbara.

At least 19 recordsLinked to original sources
PubMed2001

Suppression mediated by anergic CD4+ T cells requires stimulation by MHC-peptide complexes and can be induced in the presence of costimulation.

BACKGROUND: In this study, we have investigated the mechanisms involved in both the induction of suppressive anergy, the stability of the anergy induced, and the possible mechanisms by which the response of immunocompetent CD4+ T cells are suppressed. METHODS: We used immobilized anti-CD3 monoclonal antibody (mAb) to induce anergy in T helper (Th) 1 and Th0 cells reactive with MHC class II molecule H2 I-Ab. RESULTS: We observed that suppressive anergy was induced independently of costimulation in Th0 but not Th1 cells. Although the anergic and suppressive states of Th0 cells were stable in the presence of exogenous interleukin-2, this was not the case for Th1 cells. No evidence for linked epitope suppression was observed for any of the I-Ab reactive cells investigated. Neither anergy nor suppression was observed in Th0 cells upon restimulation with anti-CD3 in the presence of syngeneic antigen-presenting cells (APCs). However, anergy but not suppression was observed in co-cultures restimulated with anti-T-cell antigen receptor (TCR) mAbs/syngeneic APCs and suppression could be restored by the addition of I-Ab+ APCs. CONCLUSIONS: Overall, these data suggested that the MHC-peptide complex recognized by the Th0 cells was required for suppression of the response of immunocompetent cells. We propose that suppression is mediated either by down-modulation of the MHC-peptide complex recognized by the anergic T cells or that a molecule specific to the MHC-peptide/TCR interaction facilitates negative regulation by APC:T or T:T interactions.

Animals↗
PubMed2001

Evaluation of the BacT/Alert automated blood culture system for detecting bacteria and measuring their growth kinetics in leucodepleted and non-leucodepleted platelet concentrates.

BACKGROUND AND OBJECTIVE: To evaluate the BacT/Alert automated blood culture system for the detection of bacteria in platelet concentrates, and to determine bacterial growth kinetics in leucodepleted and non-leucodepleted units. MATERIALS AND METHODS: Apheresis (Cobe Leucocyte Reduction System [LRS]) and pooled buffy coat-derived (Optipress) platelet concentrates (PCs) were tested. Six organisms were used for spiking the PCs: Clostridium perfringens, Bacillus cereus, Group B Streptococcus, Staphylococcus epidermidis, Staphylococcus aureus and Escherichia coli. Units were inoculated to give a final concentration of approximately equal to 1 and 50 colony-forming units (CFU)/ml. On days 0, 2 and 5, BacT/Alert standard aerobic and anaerobic bottles were inoculated with a 5-ml fill volume and bacteria were enumerated. RESULTS: The BacT/Alert Automated blood culture system gave rapid determination times of spiked units, with all positives detected within 48 h and 98.1% detected within 24 h. In general, as the inoculum concentration increased, the detection time decreased. Rapid growth was obtained with all organisms tested except for B. cereus, which failed to grow on four occasions. Bacterial numbers on day 2 ranged from 10(5) to 10(11) CFU/ml and on day 5 ranged from 10(4) to 10(12) CFU/ml. Growth was not significantly greater in leucodepleted units. CONCLUSIONS: The study confirmed that PCs are an excellent growth medium for bacteria. Rapid and substantial growth was obtained with all organisms under test. Leucodepletion does not appear to enhance bacterial proliferation. The BacT/Alert automated blood culture system could rapidly detect contamination of units. Bacterial screening using an automated blood culture system is therefore a potential option.

Bacteria↗
PubMed2001

Evaluation of donor arm disinfection techniques.

BACKGROUND AND OBJECTIVE: To validate a standardized optimal national procedure for donor arm disinfection. MATERIALS AND METHODS: A direct swabbing and plating technique was used to enumerate bacteria present on the arm pre- and postdisinfection. Twelve donor arm disinfection techniques were evaluated. RESULTS: The Medi-Flex Adapted method, consisting of a two-stage process with an initial application of isopropyl alcohol followed by tincture of iodine, produced the best arm disinfection. A percentage reduction in bacterial counts of 99.79% (logarithmic reduction of 2.67) was obtained. Postdisinfection, 70% of donors had bacterial counts of zero, and 98% had counts of 10 or less. CONCLUSION: The Medi-Flex disinfection method offers the English National Blood Service a validated, optimal 'best practice' disinfection technique and should contribute significantly to the reduction in risk of transmission of bacteria by transfusion.

2-Propanol↗
PubMed2001

Human T-cell leukaemia/lymphoma virus risk may be enhanced in some selected donor populations.

BACKGROUND AND OBJECTIVES: Certain patient ethnic groups may require blood components from donors under-represented in the UK donor population. Selective recruitment of Afro-Caribbean donors is therefore necessary but was considered to pose an increased risk of human T-cell leukaemia/lymphoma virus (HTLV) infection. To assess this a seroprevalence study of HTLV was undertaken in Afro-Caribbean and Caucasian donors. MATERIALS AND METHODS: Sera from 1100 Afro-Caribbean and 1100 Caucasian donors were tested for antibody to HTLV. Reactive samples were confirmed for specificity using an algorithm comprising two additional assays and polymerase chain reaction (PCR) where possible. RESULTS: Six Afro-Caribbean donors (0.55%) were considered to be infected with HTLV I. CONCLUSION: Donor selection in this case caused a significantly elevated prevalence of HTLV infection and serves as a warning of the need for care in the design of policies for selective donor recruitment.

Adult↗
PubMed2001

Relationships between homocysteine and related amino acids in chronic hemodialysis patients.

AIMS: Homocysteine (Hcy) has emerged as an important risk factor for atherosclerotic disease. Elevated levels in chronic dialysis patients may contribute to high vascular mortality, but little is known about levels of related amino acids in this group. In an observational study in the clinical setting we sought to document these. METHODS: In 114 hemodialysis patients pre-dialysis total plasma homocysteine, vitamin B12 and red blood cell (RBC) folate concentrations were measured. In a subgroup of patients (n = 42), other plasma amino acids were measured pre- and post-dialysis. All patients were routinely taking oral folic acid supplements (1.2 mg per week). RESULTS: Elevated homocysteine concentrations were found in all patients (geometric mean 33.1 umol/l, range 13.8 - 69.2 umol/l, laboratory reference range (RR) 3-13 umol/l). RBC folate levels were high (1223 +/- 54.5 nmol/l mean +/- SE, RR 300 - 710 nmol/l) and inversely related to pre-dialysis plasma Hcy (r = -0.44, p < 0.001). Hcy levels were not related to vitamin B12 levels. A history of vascular disease was not associated with higher concentrations of Hcy. Hcy clearance on dialysis was substantial (mean Hcy reduction 33 +/- 14%). While plasma methionine levels were normal, serine levels were significantly lower than the reference range (59.3 +/- 2.39 umol/l (mean +/- SE, RR 70 - 195 umol/l)) and directly related to levels of glycine (r = 0.52, p < 0.001). Glycine levels were within normal range. Although overall levels were low, higher serine levels were related to elevated homocysteine (r = 0.42, p < 0.01). Dialytic loss of glycine, serine and methionine was moderate. CONCLUSION: An inverse association between RBC folate and homocysteine levels extended to 3 times the upper limit of normal for folate, suggesting a role for high dose folic acid supplementation in the treatment of renal-failure related hyperhomocysteinemia. Low serine levels are expected as it is primarily synthesized in the kidney. The direct relationship between serine and homocysteine is consistent with the reported lack of effect of serine supplements on high Hcy levels.

Amino Acids↗
PubMed2000

Islet allograft rejection can be mediated by CD4+, alloantigen experienced, direct pathway T cells of TH1 and TH2 cytokine phenotype.

BACKGROUND: It is widely believed that Thl cells that secrete interferon-gamma are primarily involved in the rejection of allografts whereas Th2 cells [interleukin(IL) 4 and IL-10] are thought to be protective of this process. However, the exact role and specificity of these helper T lymphocytes in mediating allograft damage is presently unknown. METHODS: Th0, Th1, and Th2 cell lines specific for the class II MHC molecule H2IAb were adoptively transferred into T cell deficient, syngeneic, diabetic mice before transplantation of fully allogeneic C57BL/10 (H2b) or (CBKxBALB/c)F1 (H2k/d+Kb) islet grafts. T cells were 5-(and-6-)-carboxyfluorescein diacetate succinimidyl ester- (CFSE) labeled to allow detection, immunohistochemistry was performed, and IL-4 transcripts within the rejected islet grafts were quantified by reverse transcriptase polymerase chain reaction (RT-PCR). RESULTS: Adoptive transfer (IV) of Th0-, Th1-, and Th2 IAb-specific T cells resulted in rejection of H2b islet allografts. CFSE-labeling demonstrated that these T cells were able to home to the graft site. CD4+ T cells and CD11b+ macrophages were present within the graft after adoptive transfer of both Thl and Th2 cells. Interestingly, CD8+ T cells and B cells were absent from these rejecting grafts. Even when Th2 cells were introduced directly at the graft site, prompt rejection was still observed despite the presence of increased IL-4 mRNA expression within the islet allografts. CONCLUSIONS: Th2 and Th0 alloreactive CD4+ T helper cells can reject islet grafts with similar efficiency to Th1 cells. These results suggest that deviation of the immune response from a Th1 to Th2 phenotype will not be sufficient to allow successful engraftment of allogeneic organs or tissues.

Animals↗
PubMed2000

Prospective investigation of transfusion transmitted infection in recipients of over 20 000 units of blood. TTI Study Group.

OBJECTIVES: To follow up recipients of 20 000 units of blood to identify any transmissions of infections through blood transfusion. DESIGN: Follow up study of recipients of transfusion. SETTING: 22 hospitals in north London. PARTICIPANT: Adult patients who had recently been transfused. MAIN OUTCOME MEASURES: Patients had further blood samples taken at 9 months that were tested for markers of hepatitis B and C and HIV and human T cell leukaemia/lymphoma virus type I or II (HTLV) infections. Recent infections were distinguished from pre-existing infections by comparison with blood samples taken before transfusion. RESULTS: 9220 patients were recruited, and 5579 recipients of 21 923 units of blood were followed up. No transfusion transmitted infections were identified. The incidence of transfusion transmitted infections was 0 in 21 043 units (95% confidence interval for risk 0 to 1 in 5706 recipients) for hepatitis B; 0 in 21 800 units (0 to 1 in 5911 recipients) for hepatitis C; 0 in 21 923 units (0 to 1 in 5944 recipients) for HIV; and 0 in 21 902 units (0 to 1 in 5939 recipients) for human T cell leukaemia/lymphoma virus. Three patients acquired hepatitis B during or after hospital admission but not through transfusion; 176 (3%) had pre-existing hepatitis B infection. Sixteen (0.29%) patients had hepatitis C, and five (0.09%) had human T cell leukaemia/lymphoma virus. CONCLUSIONS: The current risk of transfusion transmitted infections in the United Kingdom is very small, though hospital acquired infections may arise from sources other than transfusion. A considerable proportion of patients have pre-existing infections.

Adolescent↗
PubMed2000

Retrospective follow-up of recipients and donors of blood donations reactive for anti-HBc or for single HCV antibodies.

A retrospective study was undertaken to investigate the infectivity of blood donations that were HCV RIBA indeterminate or reactive for 'anti-HBc only'. Samples from 6032 blood donations were tested for anti-HBc; 17 of them were positive for anti-HBc but were negative when tested for anti-HBs. None of the recipients of the red cells from these donations, when tested 9 months after transfusion, had evidence of HBV infection. Samples from 3000 blood donations were tested for HCV antibodies using RIBA-3; 53 had single lines. Samples taken 9 months after transfusion from the recipients of the red cells from these donations were tested for evidence of infection with hepatitis C, and all were negative.

Blood Donors↗
PubMed2000

Which agents threaten blood safety in the future?

The safety of the blood supply is critical to many parts of modern medicine. In a time when prescriber's and the public's expectations are increasing, it is essential that transfusion services globally ensure the safety of the blood supply. There are, however, many threats to this safety, one being the appearance of new infectious agents. Such agents may be truly 'novel', or may be existing agents, known but not routinely screened for, posing a new or increased threat. However, before an agent is considered to be a true threat to blood safety it must be well characterized, and evidence must be presented that (i) transfusion transmission is a significant route of spread, and (ii) the agent causes significant clinical disease. If either of these criteria are not met, the question has to be asked as to whether the agent is truly a threat to blood safety.

Blood Transfusion↗
PubMed2000

Effects of handling and storage of blood on the stability of hepatitis C virus RNA: implications for NAT testing in transfusion practice.

BACKGROUND AND OBJECTIVES: To determine the stability of hepatitis C virus (HCV) RNA during transport and storage of blood samples from donors, prior to screening for HCV by nucleic acid amplification technology. MATERIALS AND METHODS: Various blood and plasma sample types were stored for up to 120 h at different temperatures and the HCV RNA level was measured using an in house quantitative reverse transcription-polymerase chain reaction. RESULTS: No decline in HCV RNA level was observed after 72 h of storage of whole blood at 4 degrees C in EDTA tubes (Greiner) and Plasma Preparation Tubes (PPT; Becton Dickinson), while insignificant declines of 0.2 log10 and 0. 25 log10 occurred at 25 degrees C after 72 h in the EDTA tubes and PPT tubes, respectively. When whole blood was stored with mixed anticoagulants CPDA-1 and EDTA for up to 120 h, no decline in HCV RNA level was observed at 4 degrees C and 25 degrees C, while a significant decline of 0.37 log10 occurred at 37 degrees C after 120 h. The temperature during transportation was investigated with a 12-hour period at 25 degrees C and 37 degrees C before storage at 4 degrees C for 108 h. Neither temperature resulted in any loss of HCV RNA in comparison with 120 h of storage at 4 degrees C. CONCLUSION: Whole blood anticoagulated with EDTA or CPDA-1/EDTA may be stored at up to 25 degrees C (room temperature) for up to 5 days without any significant loss in plasma HCV RNA level.

Adenine↗
PubMed2000

A UK survey of virological testing of cadaver tissue donors. Microbiology Working Group of the NIBSC steering group on Tissue/Cell Banking and Engineering.

OBJECTIVES: To analyse information about virological testing of cadaveric tissue donors, including the kits used and the rates of test reactivity. MATERIALS AND METHODS: Retrospective data were collected using a standardised questionnaire sent to 16 tissue banks in the UK. The rates of repeat reactive screen tests and confirmed positive results for the markers HBsAg, anti-HCV, anti-HIV were analysed in 1,833 cadaver tissue donors tested at 12 tissue banks over one year up to March 1998. RESULTS: There was a wide range of kits in use for virological screen testing of cadaver donors. The rates of repeat reactivity in the screen tests varied from 0 to 42%. CONCLUSION: The findings have implications for policies based on discard of tissues from donors with repeat reactive results, and raise important safety issues with regards to cadaveric virological testing, as the test systems in use have not been validated for cadaver blood samples.

Cadaver↗
PubMed1999

Serious hazards of transfusion (SHOT) initiative: analysis of the first two annual reports.

OBJECTIVE: To receive and collate reports of death or major complications of transfusion of blood or components. DESIGN: Haematologists were invited confidentially to report deaths and major complications after blood transfusion during October 1996 to September 1998. SETTING: Hospitals in United Kingdom and Ireland. SUBJECTS: Patients who died or experienced serious complications, as defined below, associated with transfusion of red cells, platelets, fresh frozen plasma, or cryoprecipitate. MAIN OUTCOME MEASURES: Death, "wrong" blood transfused to patient, acute and delayed transfusion reactions, transfusion related acute lung injury, transfusion associated graft versus host disease, post-transfusion purpura, and infection transmitted by transfusion. Circumstances relating to these cases and relative frequency of complications. RESULTS: Over 24 months, 366 cases were reported, of which 191 (52%) were "wrong blood to patient" episodes. Analysis of these revealed multiple errors of identification, often beginning when blood was collected from the blood bank. There were 22 deaths from all causes, including three from ABO incompatibility. There were 12 infections: four bacterial (one fatal), seven viral, and one fatal case of malaria. During the second 12 months, 164/424 hospitals (39%) submitted a "nil to report" return. CONCLUSIONS: Transfusion is now extremely safe, but vigilance is needed to ensure correct identification of blood and patient. Staff education should include awareness of ABO incompatibility and bacterial contamination as causes of life threatening reactions to blood.

Blood Component Transfusion↗
PubMed1999

The visualization of T cell responses.

Transplanting allogeneic grafts is still significantly hampered by the rejection process, despite the use of powerful immunosuppressive agents. The T cell is recognized as playing a central role in the process of rejection, and it is believed that graft tolerance will ultimately be achieved by immunological manipulation of this cell (1, 2). As immunologists strive to define the role of the T cell in the fundamental processes of immunity and tolerance, new methods are emerging that will facilitate visualization of the T cells directly involved in the rejection response (3, 4). This overview addresses the visualization of T cell responses as made possible by these technological developments.

Humans↗
PubMed1999

NAT: perspectives for cellular components.

The introduction of routine testing to detect viral genomes in donated blood was originally driven by requirements for plasma fractionation in relation to exclusion of hepatitis C virus (HCV) RNA. Nevertheless, it was obvious from the outset that a dual standard for fractionated products and individual blood components would be untenable. In many countries therefore, planning for introduction of nucleic acid testing (NAT) of blood incorporated progression to release of HCV RNA tested components. HCV was singled out because of its long seronegative 'window period', relatively high prevalence and incidence in blood donors, rapid burst time and high genome copy number during seroconversion. The latter properties made HCV particularly suitable for detection in pools of samples. If HCV RNA testing is required for release of labile components such as platelets, rapid provision of NAT results is vital because of short shelf life of platelets and the problems of delays when resolving the infectious unit in a reactive pool. For NAT release of labile components smaller sample pool sizes allow faster resolution of RNA positive units. Smaller pools involve high test throughput, the likely need for more testing laboratories and ensuing increased costs. Single sample testing is the ultimate extrapolation of reducing sample pool size. With reduced pool sizes or single sample testing, the option of testing for other viruses (e.g. HIV or HBV) singly or in multiplex also arises. The cost-benefit and incremental yield of such strategies in the light of 'combo' assays for HIV Ag/Ab and the recently described HCV Ag assay will require careful and objective assessment, together with re-appraisal of anti-HBc screening for detection of HBV infected donors at the "tail-end" of carriage.

Blood Cells↗