Health care professionals' experiences of pain management in the intensive care unit: a qualitative study

Despite the existence of evidence-based guidelines for the assessment and management of pain in the critical care setting, the prevalence of acute pain remains high. Inadequate pain management is associated with longer duration of mechanical ventilation, reduced capacity for rehabilitation and long-term psychological sequelae. This study aimed to describe the experiences of pain management from healthcare professionals working in intensive care units. Healthcare professionals were recruited from intensive care units in London, UK using a purposive sampling technique. Semi-structured interviews were transcribed verbatim. Transcripts were analysed using an inductive thematic analysis technique. Thirty participants were recruited from eight diverse intensive care units. Five themes were identified. First, there was a lack of consensus in pain assessment in the ICU where nursing staff described more knowledge and confidence of validated pain measures than physicians, and concerns over validity and usability were raised. Second, there was a universal perception of resource availability impacting the quality of pain management including high clinical workload, staff turnover and availability of certain pain management techniques. Third, acknowledgement of the importance of pain management was highest in those with experience of interacting with critical care survivors. Fourth, participants described their own emotional reaction to managing those in pain which influenced their learning. Finally, there was a perception that, due to the complexity of the intensive care unit population, pain was de-prioritised and there were conflicting views as to whether standardised analgosedation algorithms were useful. This study provides evidence to suggest interdisciplinary training, collaboratively designed decision-making tools, prioritisation initiatives and research priorities are areas that could be targeted to improve pain management in critical care.

1175 WAS ICU RIGHT FOR YOU? AN EXPLORATORY QUALITATIVE STUDY OF PATIENTS >=65 YRS AND NEXT OF KIN IN COVID-19: THE ESCALATE STUDY

Introduction

The decision to admit an older patient to the intensive care unit (ICU) should reflect shared goals of care. Resource limitations during the Covid-19 pandemic highlighted challenges in selecting candidates for escalation. Patients and next of kin (NoK) who have experienced ICU are well-placed to reflect on whether the admission was right for them.

Objective

To explore older patients’ (>65 years) and their loved ones’ views on escalation decision making.

Methods

Qualitative study involving semi-structured interviews with patients, NoK of survivors and NoK of deceased who experienced UK ICU admission with Covid-19 respiratory failure between March 2020 and February 2021. A preliminary questionnaire was used to maximise sample diversity of age, sex, ethnicity, survival, decision regret and impact of event scores. Interview data were collected via video conferencing or telephone. Transcripts were analysed using framework analysis. Results 30 participants were interviewed.

Results

Five themes were identified: ‘Inevitability’ - a sense that the illness and its management are out of the control of the patient or their loved one; ‘Disconnect’ - differences between hospital and lay person narratives; challenges to bridging that gap included effective communication aided by technology; ‘Acceptance’ - of the consequences, good or bad, of an intensive care admission as unalterable; ‘Beyond comprehension’ - participants had not contemplated ill health or ICU prior to admission and even with the benefit of hindsight struggled to describe which potential outcomes would be acceptable or unacceptable if they needed to be involved in similar decision-making around escalation in the future; ‘Covid-19’ - unique impact of a pandemic.

Conclusion

This study, which includes bereaved NoK as well as patients and NoK of survivors, adds perspective to inform decision making regarding treatment escalation of older people.

Patient outcomes following transfer between intensive care units during the COVID-19 pandemic

Transferring critically ill patients between intensive care units (ICU) is often required in the UK, particularly during the COVID-19 pandemic. However, there is a paucity of data examining clinical outcomes following transfer of patients with COVID-19 and whether this strategy affects their acute physiology or outcome. We investigated all transfers of critically ill patients with COVID-19 between three different hospital ICUs, between March 2020 and March 2021. We focused on inter-hospital ICU transfers (those patients transferred between ICUs from different hospitals) and compared this cohort with intra-hospital ICU transfers (patients moved between different ICUs within the same hospital). A total of 507 transfers were assessed, of which 137 met the inclusion criteria. Forty-five patients underwent inter-hospital transfers compared with 92 intra-hospital transfers. There was no significant change in median compliance 6 h pre-transfer, immediately post-transfer and 24 h post-transfer in patients who underwent either intra-hospital or inter-hospital transfers. For inter-hospital transfers, there was an initial drop in median PaO₂ /F_I O₂ ratio: from median (IQR [range]) 25.1 (17.8-33.7 [12.1-78.0]) kPa 6 h pre-transfer to 19.5 (14.6-28.9 [9.8-52.0]) kPa immediately post-transfer (p < 0.05). However, this had resolved at 24 h post-transfer: 25.4 (16.2-32.9 [9.4-51.9]) kPa. For intra-hospital transfers, there was no significant change in PaO₂ /F_I O₂ ratio. We also found no meaningful difference in pH; PaCO₂ ;_, base excess; bicarbonate; or norepinephrine requirements. Our data demonstrate that patients with COVID-19 undergoing mechanical ventilation of the lungs may have short-term physiological deterioration when transferred between nearby hospitals but this resolves within 24 h. This finding is relevant to the UK critical care strategy in the face of unprecedented demand during the COVID-19 pandemic.

The presence and potential impact of psychological safety in the healthcare setting: an evidence synthesis

INTRODUCTION

Psychological safety is the shared belief that the team is safe for interpersonal risk taking. Its presence improves innovation and error prevention. This evidence synthesis had 3 objectives: explore the current literature regarding psychological safety, identify methods used in its assessment and investigate for evidence of consequences of a psychologically safe environment.

METHODS

We searched multiple trial registries through December 2018. All studies addressing psychological safety within healthcare workers were included and reviewed for methodological limitations. A thematic analysis approach explored the presence of psychological safety. Content analysis was utilised to evaluate potential consequences.

RESULTS

We included 62 papers from 19 countries. The thematic analysis demonstrated high and low levels of psychological safety both at the individual level in study participants and across the studies themselves. There was heterogeneity in responses across all studies, limiting generalisable conclusions about the overall presence of psychological safety. A wide range of methods were used. Twenty-five used qualitative methodology, predominantly semi-structured interviews. Thirty quantitative or mixed method studies used surveys. Ten studies inferred that low psychological safety negatively impacted patient safety. Nine demonstrated a significant relationship between psychological safety and team outcomes. The thematic analysis allowed the development of concepts beyond the content of the original studies. This analytical process provided a wealth of information regarding facilitators and barriers to psychological safety and the development of a model demonstrating the influence of situational context.

DISCUSSION

This evidence synthesis highlights that whilst there is a positive and demonstrable presence of psychological safety within healthcare workers worldwide, there is room for improvement. The variability in methods used demonstrates scope to harmonise this. We draw attention to potential consequences of both high and low psychological safety. We provide novel information about the influence of situational context on an individual's psychological safety and offer more detail about the facilitators and barriers to psychological safety than seen in previous reviews. There is a risk of participation bias - centres involved in safety research may be more aligned to these ideals. The data in this synthesis are useful for institutions looking to improve psychological safety by providing a framework from which modifiable factors can be identified.

How do critical care staff respond to organisational challenge? A qualitative exploration into personality types and cognitive processing in critical care

Critical care staff are frequently required to respond to stressful scenarios. The way staff counter organisational challenge may be influenced by their underlying personality type, preferred style of cognitive processing and previous clinical experience. Our objective was to explore the personality types of a sample of critical care workers, and the potential relationship of this with cognitive processing. This was achieved through a qualitative interview study in which participants were presented with difficult but realistic scenarios pertaining to staffing. Data on individual’s personality were captured using the ‘16 Personality Factor’ assessment, a tool that produces scores for 16 different elements of an individual’s personality. The existence of perfectionist and pragmatic cognitive processing styles were identified as one theme emerging from a prior analysis of these interview transcripts. We aimed to validate this, explore our ability to categorise individuals into groups based upon their cognitive processing. We identified that some individuals strongly tended to either a perfectionist or pragmatic style of cognitive processing for the majority of their decisions; however most adapted their style of processing according to the nature of the decision. Overall participants generally demonstrated average scores for all 16 personality factors tested. However, we observed that some factors tended to higher scores than others, indicating a pattern within the personalities of our sample cohort. Whilst a small sample size, our data suggests that individuals working within the same critical care environment may have clear differences in their approach to problem solving as a consequence of both their personality type and preferred style of cognitive processing. Thus there may be individuals within this environment who would benefit from increased support to minimise their risk of cognitive dissonance and stress in times of challenge.

Leucine-enriched essential amino acid supplementation in mechanically ventilated trauma patients: a feasibility study

Background

Critically ill patients lose up to 2% of muscle mass per day. We assessed the feasibility of administering a leucine-enriched essential amino acid (L-EAA) supplement to mechanically ventilated trauma patients with the aim of assessing the effect on skeletal muscle mass and function.

Methods

A randomised feasibility study was performed over six months in intensive care (ICU). Patients received 5 g L-EAA five times per day in addition to standard feed (L-EAA group) or standard feed only (control group) for up to 14 days. C-reactive protein, albumin, IL-6, IL-10, urinary 3-MH, nitrogen balance, protein turnover ([1-13C] leucine infusion), muscle depth change (ultrasound), functional change (Katz and Barthel indices) and muscle strength Medical Research Council (MRC) sum score to assess ICU Acquired Weakness were measured sequentially.

Results

Eight patients (9.5% of screened patients) were recruited over six months. L-EAA doses were provided on 91/124 (73%) occasions. Inflammatory and urinary marker data were collected; serial muscle depth measurements were lacking due to short length of stay. Protein turnover studies were performed on five occasions. MRC sum score could not be performed as patients were not able to respond to the screening questions. The Katz and Barthel indices did not change. L-EAA delivery was achievable, but meaningful functional and muscle mass outcome measures require careful consideration in the design of a future randomised controlled trial.

Conclusion

L-EAA was practical to provide, but we found significant barriers to recruitment and measurement of the chosen outcomes which would need to be addressed in the design of a future, large randomised controlled trial.

Trial registration

ISRCTN Registry, ISRCTN79066838. Registered on 25 July 2012.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3639-2) contains supplementary material, which is available to authorized users.

Continuous monitoring and feedback of quality of recovery indicators for anaesthetists: a qualitative investigation of reported effects on professional behaviour

Background

Research suggests that providing clinicians with feedback on their performance can result in professional behaviour change and improved clinical outcomes. Departments would benefit from understanding which characteristics of feedback support effective quality monitoring, professional behaviour change and service improvement. This study aimed to report the experience of anaesthetists participating in a long-term initiative to provide comprehensive personalized feedback to consultants on patient-reported quality of recovery indicators in a large London teaching hospital.

Methods

Semi-structured interviews were conducted with 13 consultant anaesthetists, six surgical nursing leads, the theatre manager and the clinical coordinator for recovery. Transcripts were qualitatively analysed for themes linked to the perceived value of the initiative, its acceptability and its effects upon professional practice.

Results

Analysis of qualitative data from participant interviews suggested that effective quality indicators must address areas that are within the control of the anaesthetist. Graphical data presentation, both longitudinal (personal variation over time) and comparative (peer-group distributions), was found to be preferable to summary statistics and provided useful and complementary perspectives for improvement. Developing trust in the reliability and credibility of the data through co-development of data reports with clinical input into areas such as case-mix adjustment was important for engagement. Making feedback specifically relevant to the recipient supported professional learning within a supportive and open collaborative environment.

Conclusions

This study investigated the requirements for effective feedback on quality of anaesthetic care for anaesthetists, highlighting the mechanisms by which feedback may translate into improvements in practice at the individual and peer-group level.

The Faculty of Intensive Care Medicine Workforce Survey - What impacts on our working lives?

The Faculty of Intensive Care Medicine distributes an annual survey to its Consultants, allowing the evaluation of workforce profile, working patterns and the opportunity for analysis of key information on issues affecting these. We undertook an exploratory review of the data provided within the 2016 survey, with the aim of identifying themes within respondents stated career intentions and associated factors. Given the modest (36%) response rate, we are unable to draw conclusions with certainty, but there are indications within the data that the UK Intensive Care Medicine consultant body is facing significant stressors whilst at work, due to working patterns and limited resources. The data within the 2016 survey provide a base from which to develop future Faculty of Intensive Care Medicine workforce surveys that will extract data about the positive aspects of a career in intensive care medicine. The survey data provide a signal that there may be significant potentially modifiable stressors for intensive care doctors, and as such affords support for initiatives to improve job planning and sharing of implemented solutions, as well as a need to focus on workforce wellbeing as an important and necessary contributor to patient safety within intensive care medicine.

Pain Assessment in INTensive care (PAINT): an observational study of physician-documented pain assessment in 45 intensive care units in the United Kingdom

Pain is a common and distressing symptom experienced by intensive care patients. Assessing pain in this environment is challenging, and published guidelines have been inconsistently implemented. The Pain Assessment in INTensive care (PAINT) study aimed to evaluate the frequency and type of physician pain assessments with respect to published guidelines. This observational service evaluation considered all pain and analgesia-related entries in patients' records over a 24-h period, in 45 adult intensive care units (ICUs) in London and the South-East of England. Data were collected from 750 patients, reflecting the practice of 362 physicians. Nearly two-thirds of patients (n = 475, 64.5%, 95%CI 60.9-67.8%) received no physician-documented pain assessment during the 24-h study period. Just under one-third (n = 215, 28.6%, 95%CI 25.5-32.0%) received no nursing-documented pain assessment, and over one-fifth (n = 159, 21.2%, 95%CI 19.2-23.4)% received neither a doctor nor a nursing pain assessment. Two of the 45 ICUs used validated behavioural pain assessment tools. The likelihood of receiving a physician pain assessment was affected by the following factors: the number of nursing assessments performed; whether the patient was admitted as a surgical patient; the presence of tracheal tube or tracheostomy; and the length of stay in ICU. Physician-documented pain assessments in the majority of participating ICUs were infrequent and did not utilise recommended behavioural pain assessment tools. Further research to identify factors influencing physician pain assessment behaviour in ICU, such as human factors or cultural attitudes, is urgently needed.

pRotective vEntilation with veno-venouS lung assisT in respiratory failure: A protocol for a multicentre randomised controlled trial of extracorporeal carbon dioxide removal in patients with acute hypoxaemic respiratory failure

One of the few interventions to demonstrate improved outcomes for acute hypoxaemic respiratory failure is reducing tidal volumes when using mechanical ventilation, often termed lung protective ventilation. Veno-venous extracorporeal carbon dioxide removal (vv-ECCO₂R) can facilitate reducing tidal volumes. pRotective vEntilation with veno-venouS lung assisT (REST) is a randomised, allocation concealed, controlled, open, multicentre pragmatic trial to determine the clinical and cost-effectiveness of lower tidal volume mechanical ventilation facilitated by vv-ECCO₂R in patients with acute hypoxaemic respiratory failure. Patients requiring intubation and mechanical ventilation for acute hypoxaemic respiratory failure will be randomly allocated to receive either vv-ECCO₂R and lower tidal volume mechanical ventilation or standard care with stratification by recruitment centre. There is a need for a large randomised controlled trial to establish whether vv-ECCO₂R in acute hypoxaemic respiratory failure can allow the use of a more protective lung ventilation strategy and is associated with improved patient outcomes.

Risk factors for heat illness among British soldiers in the hot Collective Training Environment

Background

Heat illness is a preventable disorder in military populations. Measures that protect vulnerable individuals and contribute to effective Immediate Treatment may reduce the impact of heat illness, but depend upon adequate understanding and awareness among Commanders and their troops.

Objective

To assess risk factors for heat illness in British soldiers deployed to the hot Collective Training Environment (CTE) and to explore awareness of Immediate Treatment responses.

Methods

An anonymous questionnaire was distributed to British soldiers deployed in the hot CTEs of Kenya and Canada. Responses were analysed to determine the prevalence of individual (Intrinsic) and Command-practice (Extrinsic) risk factors for heat illness and the self-reported awareness of key Immediate Treatment priorities (recognition, first aid and casualty evacuation).

Results

The prevalence of Intrinsic risk factors was relatively low in comparison with Extrinsic risk factors. The majority of respondents were aware of key Immediate Treatment responses. The most frequently reported factors in each domain were increased risk by body composition scoring, inadequate time for heat acclimatisation and insufficient briefing about casualty evacuation.

Conclusions

Novel data on the distribution and scale of risk factors for heat illness are presented. A collective approach to risk reduction by the accumulation of ‘marginal gains’ is proposed for the UK military. This should focus on limiting Intrinsic risk factors before deployment, reducing Extrinsic factors during training and promoting timely Immediate Treatment responses within the hot CTE.

Hospital costs of out-of-hospital cardiac arrest patients treated in intensive care; a single centre evaluation using the national tariff-based system

OBJECTIVES

There is a scarcity of literature reporting hospital costs for treating out of hospital cardiac arrest (OOHCA) survivors, especially within the UK. This is essential for assessment of cost-effectiveness of interventions necessary to allow just allocation of resources within the National Health Service. We set out primarily to calculate costs stratified against hospital survival and neurological outcomes. Secondarily, we estimated cost effectiveness based on estimates of survival and utility from previous studies to calculate costs per quality adjusted life year (QALY).

SETTING

We performed a single centre (London) retrospective review of in-hospital costs of patients admitted to the intensive care unit (ICU) following return of spontaneous circulation (ROSC) after OOHCA over 18 months from January 2011 (following widespread introduction of targeted temperature management and primary percutaneous intervention).

PARTICIPANTS

Of 69 successive patients admitted over an 18-month period, survival and cerebral performance category (CPC) outcomes were obtained from review of databases and clinical notes. The Trust finance department supplied ICU and hospital costs using the Payment by Results UK system.

RESULTS

Of those patients with ROSC admitted to ICU, survival to hospital discharge (any CPC) was 33/69 (48%) with 26/33 survivors in CPC 1-2 at hospital discharge. Cost per survivor to hospital discharge (including total cost of survivors and non-survivors) was £50,000, cost per CPC 1-2 survivor was £65,000. Cost and length of stay of CPC 1-2 patients was considerably lower than CPC 3-4 patients. The majority of the costs (69%) related to intensive care. Estimated cost per CPC 1-2 survivor per QALY was £16,000.

CONCLUSIONS

The costs of in-hospital patient care for ICU admissions following ROSC after OOHCA are considerable but within a reasonable threshold when assessed from a QALY perspective.

Risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza: United Kingdom first wave (May-September 2009)

BACKGROUND

During the first wave of pandemic H1N1 influenza in 2009, most cases outside North America occurred in the UK. The clinical characteristics of UK patients hospitalised with pandemic H1N1 infection and risk factors for severe outcome are described.

METHODS

A case note-based investigation was performed of patients admitted with confirmed pandemic H1N1 infection.

RESULTS

From 27 April to 30 September 2009, 631 cases from 55 hospitals were investigated. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged > or = 65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with a severe outcome, as were radiologically-confirmed pneumonia and a raised C-reactive protein (CRP) level (> or = 100 mg/l). 59% of all in-hospital deaths occurred in previously healthy people.

CONCLUSIONS

Pandemic H1N1 infection causes disease requiring hospitalisation of previously fit individuals as well as those with underlying conditions. An abnormal chest x-ray or a raised CRP level, especially in patients who are recorded as obese or who have pulmonary conditions other than asthma or COPD, indicate a potentially serious outcome. These findings support the use of pandemic vaccine in pregnant women, children <5 years of age and those with chronic lung disease.

Cognitive dysfunction in intensive care survivors

Cognitive dysfunction is increasingly recognized as a common, often prolonged and potentially disabling complication of critical illness. While demonstrable in patients who have survived a variety of both medical and surgical conditions, its causes remain unclear. Screening of patients in intensive care units and at follow up may help identify those who could benefit from cognitive rehabilitation.

Psychological assessment of ICU survivors: a comparison between the Hospital Anxiety and Depression scale and the Depression, Anxiety and Stress scale

Recovery from a critical illness can be delayed by persistent anxiety and depression. To identify such patients, a new self-report questionnaire (the Depression, Anxiety and Stress scale, DASS) was used alongside an established instrument (the Hospital Anxiety and Depression scale, HADS) in those who had spent a minimum of 3 days (median 9 days) in a general intensive care unit. Fifty-one patients were studied 3 months later, and 45 survivors were reviewed at 9 months. High Cronbach alpha values (0.92-0.95) for each subscale of DASS confirmed its internal consistency, and likewise for HADS (0.82-0.86). HADS and DASS correlated strongly at each time point both for anxiety (r = 0.88) and depression (r = 0.93), with few discrepant values on a Bland and Altman plot. DASS performs as consistently as HADS in screening for anxiety and depression, and its psychometric properties support its use in an intensive care setting.

Long-term survival and residual hazard after in-hospital cardiac arrest

AIM

The purpose of this study was to determine long-term survival after in-hospital cardiac arrests and to explore if and when the excess mortality risk imposed by the index event reaches that of an age and sex matched general population.

METHOD

A retrospective analysis of data from 1,571 in-hospital cardiac arrests between the calendar years 1997 and 2002 inclusive was performed. Two hundred and fifty-nine people survived until hospital discharge, 220 of which were residents in England and included in the study. Kaplan-Meier curves were constructed for the survivors and an age and sex matched comparator population, and survival compared with a one-sample log rank test. Smoothed hazard curves were constructed for the two populations. Differences in outcome from year of index event were also sought.

RESULTS

16.5% of patients survived to hospital discharge. Patients continue to experience a mortality rate greater than that of the comparator population during the first 200 days, with overall 70 deaths versus 18.7 as predicted from life tables (p < 0.0001). The hazard is greatest after resuscitation and falls thereafter until about 2 years where it is not very different to that of the comparator population and then subsequently rises. No evidence was found of a difference in the first year survival between patients resuscitated in different calendar years (p > 0.3 for all tests).

CONCLUSION

The residual risk to an individual cardiac arrest survivor's life is greatest during the first year of survival, but declines progressively during the first 2 years after the event, subsequently approaching the risk experienced by the general population.

Prolonged cognitive dysfunction in survivors of critical illness

A prospective study using neuropsychological testing explored cognitive performance, and specifically executive function, in survivors of critical illness during the first year of recovery. Fifty-one patients who had survived 3 days or more in the intensive care unit were studied approximately 3 months after discharge; 45 of them were studied again 6 months later. General health was assessed using the Short-Form 36. Cognitive and executive functions were measured using Raven's Progressive Matrices, the Hayling Sentence completion test and the Six-Element Test. Three months after discharge from intensive care, all eight domains of Short-Form 36 were impaired among survivors; by 9 months, four of the eight domains showed significant improvement. At 3 months, 35% of patients scored at or below a level equivalent to the lowest performing 5% of a normal population (i.e. the fifth percentile) on two or more tests of cognitive function; by 9 months only 4% of patients were impaired to this extent. Although cognitive performance improved with time, it remained below normal.

A survey of physicians' attitudes to transfusion practice in critically ill patients in the UK

This study aimed to examine the attitudes of intensivists and haematologists to the use of blood and blood products using a scenario-based postal questionnaire. One hundred and sixty-two intensivists and 77 haematologists responded to the survey. In four scenarios, the baseline haemoglobin thresholds for red cell transfusion ranged from 6 to 12 g.dl(-1). There was significant variation between scenarios (p <0.005). Increasing age, high Acute Physiology and Chronic Health Status II score, surgery, acute respiratory distress syndrome, septic shock and lactic acidosis significantly (p <0.005) modified the transfusion threshold. There were greater variations in the baseline threshold for platelet transfusion. The majority of respondents (72.3%) selected a baseline haemoglobin threshold between 9 and 10 g.dl(-1). The thresholds for platelet transfusion were far less consistent.

Blood component use in critically ill patients

This prospective observational study was conducted to assess the current transfusion practice in critically ill patients. One thousand two hundred and forty-seven consecutive critically ill patients admitted between February 1999 and October 1999 were included in the study. Overall 666 (53%) patients were administered red cells. Transfused patients had significantly higher intensive care unit mortality but also had higher Acute Physiology and Chronic Health Evaluation II scores and longer durations of stay. The average pretransfusion haemoglobin concentration was < 9 g.dl(-1) in 75% of transfusion episodes. The common indications for transfusion were low haemoglobin (72%) and haemorrhage (25%). Overall, 202 (16%) and 281 (22%) of the patients were transfused platelets and fresh frozen plasma, respectively. The indications for transfusion were haemorrhage, low platelet counts, prolonged prothrombin time or to provide cover for invasive interventions. Most platelet transfusions were given at values in the order of 50-100 x 10(9).l(-1). The pretransfusion platelet count varied according to the indications for transfusion. This study showed that transfusion practice is consistent and that in general there does not seem to be an excessive use of blood components in critically ill patients.

Expression of L-selectin on Th1 cells is regulated by IL-12

L-selectin has become established as a key molecule in the recirculation of naïve T cells from the blood to peripheral lymph nodes, yet little is known about its role in the migration of effector or memory cells. While differentiating naïve CD4+ T cells into Th1 and Th2 subsets in vitro, it was noted that L-selectin levels were maintained on the Th1 subset of cells. The expression of L-selectin on the Th1 cells appeared to be dependent on the presence of IL-12. Th2 cells, differentiated in the absence of IL-12, failed to maintain L-selectin expression. Coculture with IL-12, IL-18, IL-4, TNF-alpha, or IFN-alpha, -beta, or -gamma demonstrated a dependence on IL-12 alone for L-selectin expression. In addition, the inclusion of heat-killed Listeria monocytogenes in the cultures also maintained L-selectin expression on the Th1 cells. In all cultures, the maintenance of L-selectin on the T cell surface could be blocked by the inclusion of anti-IL-12 Abs. Analysis of the mRNA levels for L-selectin in T cells, differentiated in the presence or absence of IL-12, showed that the cytokine appears to exert its effect on L-selectin at the transcriptional level. Given the key role played by IL-12 in the differentiation of naïve T cells into the Th1 subset, the observation that IL-12 can also regulate L-selectin expression has implications for the migration of Th1 effector cells both through the lymphatic system and to sites of inflammation.

Clinical correlates in acute lung injury: response to inhaled nitric oxide

STUDY OBJECTIVES

The use of inhaled nitric oxide (NO) in the management of patients with ARDS has become widespread, although not all patients respond to this form of support. The aim of this study was to examine the relationship of responsiveness to inhaled NO and features of underlying disease.

DESIGN

Prospective observational study.

SETTING

The ICU of a university-affiliated, tertiary referral hospital.

PATIENTS

Twenty-six adult patients with established ARDS.

INTERVENTIONS

Conventional support for multiple organ failure, plus inhaled NO.

MEASUREMENTS AND RESULTS

Response to inhaled NO was assessed, and ARDS was characterized in terms of pulmonary morphology (scoring of high-resolution CT); inflammation (BAL neutrophil count and plasma myeloperoxidase concentration); and markers of lung injury severity (oxygenation deficit and pulmonary vascular resistance [PVR]). Fourteen patients responded to NO and 12 did not. There were no differences between the two groups in terms of CT score, inflammatory status, baseline oxygenation deficit, lung injury score, or PVR. Additionally, there was no difference in survival between responders and nonresponders. Patients who developed ARDS after thoracic surgery were significantly more likely to die than other patients (relative risk 4.1, p < 0.01). The oxygenation deficit and lung injury score correlated better with the extent of ground-glass opacification than with the volume of consolidated lung tissue.

CONCLUSION

We were unable to identify features of disease likely to be associated with a clinically useful response to inhaled NO therapy using the parameters studied.

Cross-linking of the CAMPATH-1 antigen (CD52) mediates growth inhibition in human B- and T-lymphoma cell lines, and subsequent emergence of CD52-deficient cells

The CAMPATH-1H (CD52) antigen is a 21 000-28 000 MW glycopeptide antigen that is highly expressed on T and B lymphocytes and is coupled to the membrane by a glycosylphosphatidylinositol (GPI) anchoring structure. The humanized CAMPATH-1H anti-CD52 antibody is extremely effective at mediating depletion of both normal and tumorigenic lymphocytes in vivo and has been used in clinical trials for lymphoid malignancy and rheumatoid arthritis. Cross-linking GPI-anchored molecules, including CD52, on the surface of T lymphocytes in the presence of phorbol 12-myristate 13-acetate or anti-CD3, results in cellular activation. In the present study we have investigated the functional effects of cross-linking CD52 on T and B tumour cell lines. Cross-linking CD52 on either a B-cell line, Wien 133, which expresses high levels of endogenous CD52 or Jurkat T cells transfected and selected to express high levels of CD52 resulted in growth inhibition. This effect showed slower kinetics and occurred in a lower percentage of cells than growth inhibition stimulated via T- or B-cell receptors. Growth inhibition of the Wien 133 line was followed by the induction of apoptosis, which appeared independent of the Fas/Fas L pathway. Wien 133 cells surviving anti-CD52 treatment were selected and cloned and found to have down-regulated CD52 expression, with a characteristic biphasic pattern of 10% CD52-positive, 90% negative by fluorescence-activated cell sorter analysis. Interestingly, surface expression of other GPI-linked molecules, such as CD59 and CD55, was also down-regulated, but other transmembrane molecules such as surface IgM, CD19, CD20, HLA-DR were unaffected. The present study and previous work show that this is due to a defect in the synthesis of mature GPI precursors. Separation of CD52-positive and negative populations in vitro resulted in a rapid redistribution to the mixed population. Injection of CD52-negative cells into nude mice to form a subcutaneous tumour resulted in a substantial increase in expression of CD52. These results suggest that the defect in the Wien 133 cells is reversible, although the molecular mechanism is not clear. These observations have relevance to the clinical situation as a similar GPI-negative phenotype has been reported to occur in lymphocytes following CAMPATH-1H treatment in vivo.

Pulmonary response of normal human subjects to inhaled vasodilator substances

1. Inhaled vasodilators such as nitric oxide and epoprostenol (prostaglandin I2) are now widely employed as supportive therapies to improve oxygenation and reduce pulmonary vascular resistance in patients with acute and chronic pulmonary hypertension. However, few data exist concerning their effects in normal individuals. The aim of this study was to characterize the response of the pulmonary circulation in normal individuals to inhaled nitric oxide and nebulized prostaglandin I2.2.Eight healthy volunteers were exposed to inhaled nitric oxide (0, 20 and 40 p.p.m.) and nebulized prostaglandin I2 (10 microgram/ml). Changes in effective pulmonary blood flow and diffusing capacity of the lung for carbon monoxide (TLCO) were measured using respiratory mass spectrometry. Bicycle ergometry was used to increase effective pulmonary blood flow as a positive control.3. Exercise produced significant increases in both effective pulmonary blood flow and TLCO, but neither nitric oxide nor prostaglandin I2 produced significant changes in either parameter.4.No significant change in pulmonary haemodynamics was demonstrated in response to inhaled nitric oxide or nebulized prostaglandin I2, using doses known to be effective in patients with acute and chronic pulmonary hypertension. These data suggest that the normal pulmonary vascular bed is not amenable to vasodilatation by inhaled drugs. The study further suggests that the normal pulmonary vasodilatation seen on exercise is not mediated pharmacologically, but is a secondary consequence to the mechanical effects of a rise in pulmonary blood flow. This study thus supports the view that there is no resting vasoconstrictor tone in the pulmonary vascular bed.

Reduced mortality in association with the acute respiratory distress syndrome (ARDS)

BACKGROUND

A study was undertaken to investigate possible reductions in mortality and/or changes in outcome predictive factors in patients with the acute respiratory distress syndrome (ARDS) managed in a single centre.

METHODS

The study was a prospective observational cohort study of two patient populations with ARDS. Group 1 comprised 41 patients enrolled between May 1990 and April 1993, and group 2 consisted of 78 patients enrolled between June 1993 and March 1997. The end points of the study were mortality and various factors predictive of death.

RESULTS

There was a marked reduction in mortality between groups 1 and 2 (66% versus 34%; relative risk 1.77; CI 1.23 to 2.55). There were no significant differences between the groups in terms of age (40.6 (3.3) versus 45.5 (2.2) years), APACHE score (14.5 (0.72) versus 13.6 (0.1)), lung injury score (2.95 (0.07) versus 2.8 (0.1)), incidence of multi-organ failure (29% versus 32%), incidence of sepsis (31% versus 39%), or PaO2/FIO2 (kPa) ratio (11.8 (0.67) versus 12.0 (0.6)). There was a significantly lower proportion of men in group 1 (51% versus 74%). The case mix of the two groups was closely matched: following elective surgery 48% versus 48%, trauma 17% versus 16%, primary lung injury 12% versus 24%. Patients in group 1 were supported using several ventilatory and other modes (volume preset, non-inverse ratio ventilation, n = 15; pressure controlled inverse ratio ventilation (PC-IRV), n = 11; ultra high frequency jet ventilation (UHFJV), n = 13; an intravascular oxygenation device (IVOX) and extracorporeal gas exchange (ECGE), n = 2). Within group 1 no significant difference in mortality was observed between the patients on volume controlled ventilation and the remainder. In group 2 all patients received PC-IRV (n = 78) but, in addition, some received other support techniques (UHFJV n = 4, ECGE n = 2). In group 1 only sepsis on admission (21% (survivors) versus 56% (non-survivors)) predicted death. In group 2 age of survivors and non-survivors (41.2 (2.6) versus 52.6 (3.5)), APACHE score (12.2 (0.6) versus 15.8 (0.9)), and PaO2/FIO2 (12.8 (0.86) versus 10.5 (0.72)) predicted survival, but not the incidence of sepsis or multi-organ failure.

CONCLUSIONS

In recent years a highly significant reduction in mortality associated with ARDS has been observed between two groups of patients well matched for disease severity and case mix. Changes in ICU organisation rather than specific interventions may account for this reduction, although different ventilatory and other management strategies used in the two groups may also be relevant.

Measurement of endogenous nitric oxide in the lungs of patients with the acute respiratory distress syndrome

Elevated levels of nitric oxide (NO) are detectable in the exhaled breath of patients suffering from a number of inflammatory lung diseases. We hypothesized that NO would be detectable in the exhaled air of patients with the acute respiratory distress syndrome (ARDS) undergoing mechanical ventilation and that the concentration would be greater than that from a control group of ventilated subjects. The concentration of NO in the lower airways of 13 patients with ARDS and 18 patients anesthetized and ventilated prior to cardiac surgery was measured by chemiluminescence. The NO concentration was 1.13 +/- 0.36 (mean +/- SEM) parts per billion (ppb) in the ARDS group and 5.5 +/- 0.8 ppb in the control group (2 p < 0.0001). NO is detectable in the exhaled air of patients with ARDS and is at a lower concentration than in control subjects.

Production of nitric oxide during surgery involving cardiopulmonary bypass

OBJECTIVES

Surgery involving cardiopulmonary bypass induces an inflammatory response due to the contact of blood with the extracorporeal circuit. In some patients, this inflammatory response leads to multiple organ failure and death. Inflammatory states may increase the production of nitric oxide, either by increasing the activity of constitutive enzyme systems or by inducing of inflammation-specific systems. We hypothesized that surgery involving cardiopulmonary bypass would increase the production of nitric oxide in association with the inflammatory response.

DESIGN

Prospective, single center, observational study.

SETTING

University-affiliated, tertiary referral cardiothoracic center.

PATIENTS

Eleven adult patients undergoing routine myocardial revascularization.

INTERVENTIONS

Surgery for myocardial revascularization.

MEASUREMENTS AND MAIN RESULTS

Observations were made after induction of anesthesia, before bypass, after completion of the bypass, and on return to the recovery area. Parameters measured included hemodynamics, exhaled nitric oxide concentrations, plasma nitrate/nitrite concentration, plasma and bronchoalveolar lavage myeloperoxidase concentrations, and protein carbonyl conversion. All patients survived surgery. Oxygenation index fell significantly after bypass. Plasma myeloperoxidase increased significantly during the study period. Plasma carbonyl conversion also increased, although not significantly. Plasma nitrate/nitrite and airway nitric oxide concentrations did not change through the course of the study.

CONCLUSION

Surgery involving cardiopulmonary bypass induced a demonstrable inflammatory response, but this response was not associated with increased nitric oxide production.

Differential functional effects of a humanized anti-CD4 antibody on resting and activated human T cells

A fully humanized immunoglobulin G1 (IgG1) anti-CD4 monoclonal antibody is currently being evaluated in phase I/II clinical trials for rheumatoid arthritis. In order to understand the mode of action of this antibody in vivo, we have carried out a detailed functional analysis in vitro of the effects of this antibody on T-cell activation. The anti-CD4 antibody was found to inhibit both antigen-specific responses involving recognition of human leucocyte antigen (HLA) class II and processed antigenic peptides as well as non-class II dependent responses via anti-CD3 antibodies. The antibody did not cause total blockade of T-cell proliferation, but rather induced a shift in the dose-response curve, decreasing the sensitivity of cells to antigen or anti-CD3-mediated stimulation. The antibody appears to allow at least a partial early signal into the T cell as it does not inhibit the increase in tyrosine phosphorylation induced by anti-CD3 antibodies. A comparison of the intact antibody with that of either the F(ab')2 fragment or an engineered non-Fc receptor (FcR) binding form revealed that the intact antibody was the most effective at inhibiting proliferation of resting peripheral blood CD4+ T cells. However, this difference was only apparent when excess antibody was removed from culture prior to antigen or anti-CD3 mediated stimulation. The intact antibody induced both CD4 down-modulation and increases in CD4-associated tyrosine phosphorylation of resting CD4+ T cells, which were not seen with the non-FcR binding versions, which may account for the enhanced potency of the intact antibody at inhibiting T-cell activation. Interestingly, the anti-CD4 antibody induced a differential effect on activated CD4+ T cell clones compared with resting CD4+ T cells with respect to degree of CD4 cross-linking required to induce functional effects in the T cell. Both intact and non-FcR binding antibodies were equally effective at inhibiting T-cell proliferation of activated T-cell clones. In addition CD4 down-modulation and increased CD4-associated tyrosine phosphorylation were observed with T-cell clones in the absence of secondary cross-linking. Such observations may be of relevance when studying the effects of the antibody at sites of inflammation, where there will be CD4+ T cells of differing activation states as well as varying numbers of FcR positive cells.

Quantitative but not qualitative variation in MHC class II alters CD4 interaction and influences T cell repertoire formation

The influence of the interaction between CD4 and MHC class II molecules on selection of the T cell repertoire was studied in transgenic mice expressing human or human/mouse hybrid MHC class II beta chains. Either wild-type DR beta chains (DR1 beta) or hybrid beta chains comprising the beta1 domain of DR and the beta2, transmembrane, and intracytoplasmic domains of I-E (DRbeta 1Ebeta2) were introduced into and expressed in transgenic mice as a heterodimer with endogenous I-E alpha. Mice expressing low levels of DR1beta:I-E alpha or those expressing low or higher levels of the hybrid DRbeta 1Ebeta2:I-E alpha were studied. Immunization with a suboptimal dose of influenza nucleoprotein peptide exposed a fivefold lower frequency of DR-restricted, peptide-specific, IL-2-secreting T cells in the mice with low-level expression of DRbeta1 Ebeta2:I-E alpha when compared to mice expressing the same molecule at higher levels. The frequency in DRbeta wild-type mice was only twofold lower than that measured in mice with comparable levels of expression of DRbeta 1Ebeta2. These results suggest that positive selection is sensitive to quantitative variation in MHC class II density, unmasked when antigen is limiting, but is relatively insensitive to qualitative variation in the MHC class II: CD4 interaction.

Emergence of CD52-, glycosylphosphatidylinositol-anchor-deficient lymphocytes in rheumatoid arthritis patients following Campath-1H treatment

CD52 is a glycosylphosphatidyl-inositol (GPI)-linked glycoprotein expressed at high levels on normal T and B lymphocytes and at lower levels on monocytes, while being absent on granulocytes and bone marrow stem cell precursors. The emergence of CD52- lymphocytes of both T and B cell lineages was observed in three out of 25 rheumatoid arthritis patients treated with teh humanized antibody Campath-1H in phase II clinical trial. Whereas the majority of CD52- B cells had disappeared from the peripheral blood by 3 months post-treatment, both CD52- CD4+ and CD8+ T cells persisted in the circulation for at least 20 months. In the two patients that were tested, the GPI-anchored surface molecules CD55 and CD59 were also absent on the CD52- cells, although expression of other cell surface transmembrane, proteins (CD3, CD4 and CD2) was unaffected. The CD52- cells maintained a stable phenotype in vitro despite repeated re-stimulation in culture. Both CD52- and C52+ clones, established from one of the patients, responded to a similar extent to several T cell mitogens, as assessed by proliferation, suggesting that a general defect in expression of GPI-linked molecules does not impair T cell activation. These data show that an immune attack against a GPI-anchored surface molecule can result in the selection of a GPI-anchor-deficient cell population. Despite the persistence of CD52- T cells in the peripheral blood, no adverse reactions associated with the presence of these cells were noted in any of the patients; in fact they responded with longer remission times after Campath-1H treatment than the other patients in the trial.

Both H-2- and non-H-2-linked genes influence influenza nucleoprotein epitope recognition by CD4+ T cells

The specificity of the influenza nucleoprotein-induced T-cell proliferative response by mouse strains differing in either H-2- or non-H-2-linked background genes was compared by using a panel of synthetic peptides covering 90% of the nucleoprotein molecule. The results showed, as expected, that H-2 genes strongly influenced the major regions of the molecules recognized by T cells, as the response was focused on different peptides in mice of different H-2 haplotypes. However, some regions of the molecule (e.g. 260-283) were recognized by several different haplotypes, with overlapping but distinct minimal determinants. The lymph node proliferative response appeared to be predominantly restricted by the I-A molecule, as expression of I-E in mice did not result in any detectable recognition of additional epitopes. In the majority of cases the same T-cell epitopes were recognized by mouse strains sharing the same H-2 haplotype but differing in many background genes. Low responsiveness was however observed to p55-77 by DBA/2 and p127-141 by AKR mice to which other H-2d or H-2k strains were high responders. Low responsiveness is therefore unlikely to be a consequence of failure of these peptides to bind to the relevant major histocompatibility complex class II molecule. In addition antigen-presenting cells from the DBA/2 low responder strain was able to process and present whole influenza virus or nucleoprotein as well as antigen-presenting cells from the high responder BALB/c strain. It is therefore suggested that low responsiveness to the peptide p55-77 may be due to a 'hole in the T-cell repertoire', caused perhaps by expression of Mls-1a in the DBA/2 strain. This is supported by the observation that low responsiveness to this epitope appears to be dominant in F1 (low x high) mice.

Impairment of endothelium-dependent pulmonary vasodilation in patients with primary pulmonary hypertension

BACKGROUND

Pulmonary vascular tone may be modulated by endothelium-derived vasoactive mediators. Endothelial dysfunction is thought to occur in primary pulmonary hypertension. The aim of this study was to evaluate the vascular responses of patients with severe primary pulmonary hypertension to endothelium-dependent vasodilators (for example, substance P) and non-endothelium-dependent vaasodilators (for example, adenosine).

METHODS

Six patients with primary pulmonary hypertension (mean (SE) systolic, diastolic, and pulmonary artery pressures 91.1 (7), 45.2 (3), and 62 (4.2) mm Hg, respectively, and baseline total pulmonary vascular resistance (TPVR) 1949 (164) dynes.s.cm-5) underwent sequential infusions of substance P (5-100 pmol/min) and adenosine (5-50 micrograms/kg/min) in random order. Pulmonary and systemic haemodynamics were monitored by indwelling radial and pulmonary arterial catheters.

RESULTS

Substance P caused a marked fall in systemic vascular resistance (SVR) but minimal pulmonary vasodilation (mean maximal percentage change from baseline in TPVR:SVR ratio 27.85 (6.5)%, p < 0.01). Adenosine caused TPVR to fall, but resulted in no change in SVR (mean maximum percentage change from baseline in TPVR:SVR ratio -9.85 (3.5)%, p < 0.05).

CONCLUSION

Endothelium-dependent vasodilation is deficient in the pulmonary circulation of patients with primary pulmonary hypertension and may contribute to the abnormalities of pulmonary vascular tone and reactivity seen in that condition.

Cross-linking of the CAMPATH-1 antigen (CD52) triggers activation of normal human T lymphocytes

The CAMPATH-1 (CD52) antigen is a 21-28 kDa glycopeptide which is highly expressed on lymphocytes and macrophages and is coupled to the membrane by a glycosylphosphatidylinositol (GPI) anchoring structure. The function of this molecule is unknown. However, it is an extremely good target for complement-mediated attack and antibody-mediated cellular cytotoxicity. The humanized CAMPATH-1H antibody, which is directed against CD52, is very efficient at mediating lymphocyte depletion in vivo, and is currently being used in clinical trials for lymphoid malignancy and rheumatoid arthritis. It is therefore important to examine the functional effects of this antibody on different lymphocyte sub-populations. Because several other GPI-linked molecules expressed on the surface of T lymphocytes are capable of signal transduction resulting in cell proliferation, we have investigated whether the CAMPATH-1 antigen can also mediate these effects. In the presence of phorbol esters and cross-linking anti-Ig antibodies, mAbs specific for CD52 induced proliferation and lymphokine production in highly purified resting CD4+ and CD8+ T lymphocytes. The rat IgG2c YTH 361.10 anti-CD52 antibody, however, was able to activate resting CD4+ and CD8+ T cells directly without cross-linking or phorbol myristate acetate in the absence of Fc-bearing cells. Anti-CD52 antibodies also augmented the anti-CD3 mediated proliferative response of CD4+ and CD8+ T cells when the two antibodies were co-immobilized onto the same surface or cross-linked in solution by the same second antibody. Both CD4+ CD45RA and CD4+ CD45RO T cells were stimulated to proliferate by anti-CD52 antibodies in the presence of appropriate co-stimulatory factors. Anti-CD52 mAbs did not, however, synergize with anti-CD2 or CD28 mAb to induce CD4+ T cell proliferation. The activation of CD4+ T cells by anti-CD52 antibodies was inhibited by cyclosporin A, suggesting a role for the calcineurin-dependent signal transduction pathways. Although CD52 could transduce a signal in T cells, anti-CD52 antibodies did not inhibit antigen-specific or polyclonal T cell responses, suggesting this molecule does not play an essential co-stimulatory role in normal T cell activation.

Epitope specificity and isoforms of the mycobacterial 19-kilodalton antigen

The topography and specificity of B- and T-cell stimulatory epitopes from the 19-kDa protein of Mycobacterium tuberculosis were investigated by using overlapping synthetic peptides. Murine antisera identified two cryptic epitopes (residues 11 to 30 and 61 to 80) and one species-specific immunodominant epitope (residues 140 to 159). Immunoglobulins G1 and G2a antibody isotypes varied for the respective peptide immunogens but without relationship to the T-cell cytokine profiles which were characterized by high gamma interferon and low interleukin 5 levels. Antisera to recombinant M. tuberculosis 19-kDa protein (rGST-19) cross-reacted with homologous proteins of similar size from organisms of the Mycobacterium avium-intracellulare complex. Two-dimensional gel electrophoresis revealed differences in the number, relative mobility, and charge of isoforms of the 19-kDa protein, possibly reflecting posttranslational modifications. The immunodominant T-cell epitope from the M. tuberculosis 19-kDa protein (residues 61 to 80) and the corresponding peptide sequence from Mycobacterium avium subsp. intracellulare (residues 64 to 83), differing at five residues, were both recognized in a genetically permissive manner. Peptides 61-80 and 64-83 stimulated cross-reactive responses in BALB/c (H-2d) mice, while in the C57BL/10 (H-2b) strain, responses to peptide 61-80 were species specific. In purified protein derivative-positive healthy individuals, the M. avium subsp. intracellulare peptide stimulated stronger responses than did the M. tuberculosis peptide, whereas patients with active tuberculosis had enhanced in vitro T-cell responses to both peptides.

Influence of the antigen delivery system on immunoglobulin isotype selection and cytokine production in response to influenza A nucleoprotein

The influence of different antigen delivery systems on antibody isotype and lymphokine profile has been investigated using influenza nucleoprotein as a model antigen system. Mice exposed to live or inactivated influenza virus produced antibody against whole virus or recombinant nucleoprotein (rNP), which was predominantly of the IgG2a isotype. Spleen or lymph node cells from these mice rapidly produced large amounts of interferon-gamma (IFN-gamma), but no detectable interleukin-5 (IL-5) when stimulated in vitro with specific antigen. In contrast, after primary immunization with rNP or p206-229 in different adjuvants (CFA, quil A or alhydrogel), specific antibody was predominantly of the IgG1 isotype and relatively lower amounts of IFN-gamma but no IL-5 were detected following in vitro antigenic stimulation. Secondary immunization, however, resulted in detection of IgG2a antibodies and increased levels of IFN-gamma. IL-5 was only detected after secondary immunization with peptide in adjuvant. Mice infected with aro A- Salmonella typhimurium expressing NP produced antibody of both IgG1 and IgG2a isotypes and large amounts of IFN-gamma and no IL-5, following in vitro antigenic stimulation, and therefore parallelled the pattern seen with whole virus more closely than that seen following primary immunization with protein or peptide in conventional adjuvants. The results suggest that the antigen delivery vehicle influences both quantitative and qualitative differences in the type of immune response elicited, which may be important in determining the potency of protective immunity induced.

Pre-exposure of murine macrophages to lipopolysaccharide inhibits the induction of nitric oxide synthase and reduces leishmanicidal activity

Murine macrophages produce nitric oxide (NO) from L-arginine on stimulation with lipopolysaccharide (LPS), alone or with interferon-gamma (IFN-gamma). The effect of incubation of macrophages with low concentrations of LPS on NO synthesis on subsequent stimulation was investigated, using a murine macrophage cell line, J774, and peritoneal macrophages from CBA mice. Cells which had been incubated with LPS produced significantly lower amounts of NO, and expressed lower levels of NO synthase activity, following stimulation with IFN-gamma and LPS, or with a high concentration of LPS. This effect was not reversed by tumor necrosis factor-alpha. The ability of CBA macrophages to kill the intracellular parasite Leishmania major was markedly reduced by pre-incubation with LPS. Reduced NO production by macrophages previously exposed to LPS is a manifestation of endotoxin tolerance, and may represent an important means of regulation of NO synthesis and thus a survival mechanism for intracellular parasites.

The invasin protein of Yersinia spp. provides co-stimulatory activity to human T cells through interaction with beta 1 integrins

The invasin proteins of Yersinia spp. are outer membrane proteins which are involved in the penetration of these bacteria into mammalian cells (Cell 1990. 60: 861). Invasin binds to several different beta 1 integrins with extremely high affinity, the integrin-binding domain of invasin has been mapped to the C-terminal 192 amino-acids of the molecule (J. Biol. Chem. 1991. 266:24367). Expression of this fragment alone on the cell surface of non-invasive bacteria is enough to confer the invasive phenotype on these strains (EMBO J. 1990. 9: 1979). Here we show that the carboxy-terminal 192 amino acids of invasin expressed as a fusion protein with the maltose binding protein of E. coli is capable of delivering co-stimulatory signals to human T cells through the beta 1 integrins. Co-stimulation was assayed by the ability of invasin to augment the response of highly purified CD4+ and CD8+ T cells to co-immobilized anti-CD3 antibody. Antibody blocking studies indicated that the co-stimulation was mediated through beta 1 integrins. The proliferation induced by co-stimulation of CD4+ T cells was accompanied by the synthesis of the cytokines tumor necrosis factor-alpha and interferon-gamma, whereas the activation of CD8+ T cells led to the generation of cytotoxic effectors. The region of the invasin molecule involved in T cell activation was further mapped using synthetic peptides. A region of the invasin molecule containing the residues TAKSKKFPSY could substitute for invasin in T cell activation. The co-stimulation by peptide could also be inhibited by anti-integrin antibodies. The observation that an outer membrane protein of a bacterium which is associated with reactive arthritis and other autoimmune spondyloarthropathies can act as a T cell co-stimulus may have implications for the etiology of these diseases.

Comparison of antigen presentation of influenza A nucleoprotein expressed in attenuated AroA- Salmonella typhimurium with that of live virus

Rationally attenuated strains of Salmonella expressing foreign proteins represent a potentially important vaccine delivery system. The characteristics of Ag presentation of influenza nucleoprotein expressed in an AroA- strain of Salmonella typhimurium (SL3262-pNP-2) have therefore been compared with those of soluble purified nucleoprotein (NP) and infectious influenza virus. This represents three distinct modes of internalization of the same protein into APC. Human monocytes and the monocytic leukemia cell line THP-1 infected with SL3261-pNP-2 were found to present several different epitopes from NP to human CD4+ class II-restricted T lymphocytes. Ag presentation to these T cell clones was enhanced by pretreatment of THP-1 cells with IFN-gamma but not TNF-alpha. Bacterial phagocytosis and Ag presentation of NP were increased after opsonization of Salmonella with immune serum. Macrophages infected with SL3261-pNP-2 were unable to present NP to class I-restricted T cells. In contrast, cells infected with live influenza virus, although recognized by NP-specific class I-restricted CTL, were inefficiently recognized by NP-specific class II-restricted T cells. Ag presentation to CD4+ T cell clones by monocytes of SL3261-pNP-2, purified recombinant NP, and live influenza virus, but not the synthetic peptide 206-229, was inhibited by chloroquine and the protease inhibitors pepstatin A and leupeptin, suggesting that the major route of processing in each case was via the exogenous pathway. T cell recognition of NP via all of these Ag delivery systems was also abrogated by cycloheximide and brefeldin A treatment, indicating a requirement for recently synthesized MHC class II molecules in presentation of whole NP after processing but not for the corresponding synthetic peptide.

Immunological analysis of the zinc-binding peptides of surface metalloproteinase (gp63) of Leishmania major

The surface metalloproteinase, gp63, is highly conserved and immunogenic. A peptide spanning the zinc-binding region of the molecule is immunogenic and can induce protective immunity in mice against Leishmania major infection. We report here that the minimum length of the immunogenic peptide in this region is a heptapeptide, VVTHEMA, corresponding to residues 161-167. Optimal immunogenicity is conferred by a decapeptide, LVTVVTHEMA, corresponding to residues 158 to 167, where H and E are consensus zinc-binding residues. These two residues determine the specificity of the peptide. The next two residues, M and A are necessary for the immunogenicity of the peptide. These results suggest that the zinc-binding residues are recognized by the T-cell receptor complex, while the two adjacent residues are involved in the peptide presentation by the major histocompatibility complex (MHC) molecule.

Comparison of antigen presentation of influenza A nucleoprotein expressed in attenuated AroA- Salmonella typhimurium with that of live virus

Rationally attenuated strains of Salmonella expressing foreign proteins represent a potentially important vaccine delivery system. The characteristics of Ag presentation of influenza nucleoprotein expressed in an AroA- strain of Salmonella typhimurium (SL3262-pNP-2) have therefore been compared with those of soluble purified nucleoprotein (NP) and infectious influenza virus. This represents three distinct modes of internalization of the same protein into APC. Human monocytes and the monocytic leukemia cell line THP-1 infected with SL3261-pNP-2 were found to present several different epitopes from NP to human CD4+ class II-restricted T lymphocytes. Ag presentation to these T cell clones was enhanced by pretreatment of THP-1 cells with IFN-gamma but not TNF-alpha. Bacterial phagocytosis and Ag presentation of NP were increased after opsonization of Salmonella with immune serum. Macrophages infected with SL3261-pNP-2 were unable to present NP to class I-restricted T cells. In contrast, cells infected with live influenza virus, although recognized by NP-specific class I-restricted CTL, were inefficiently recognized by NP-specific class II-restricted T cells. Ag presentation to CD4+ T cell clones by monocytes of SL3261-pNP-2, purified recombinant NP, and live influenza virus, but not the synthetic peptide 206-229, was inhibited by chloroquine and the protease inhibitors pepstatin A and leupeptin, suggesting that the major route of processing in each case was via the exogenous pathway. T cell recognition of NP via all of these Ag delivery systems was also abrogated by cycloheximide and brefeldin A treatment, indicating a requirement for recently synthesized MHC class II molecules in presentation of whole NP after processing but not for the corresponding synthetic peptide.

Measurement of the immunoperoxidase staining of macrophages within liver granulomata of mice infected with Mycobacterium tuberculosis

A quantitative image analysis technique developed for the measurement of the extent of macrophage activation and epithelioid cell differentiation was performed on mice infected experimentally with Mycobacterium tuberculosis. The granulomatous inflammatory response within the liver reached a peak at day 23 and declined by day 33. Animals of strain B10.BR (H-2k) showed an increased granuloma fraction as compared to Balb/k (H-2k) mice, thus confirming the influence of non-H2 genes in the control of granuloma formation in mice. Using a monoclonal antibody against CD11b/CD18 (Mac1;CR3), we observed two subpopulations of macrophages within the granulomata. The small, darkly staining cells at the periphery of granulomata appear to be newly recruited macrophages. Larger, paler staining cells toward the center of granulomata represent activated and mature epithelioid macrophages. Using a semiautomated image analyzer (Quantimet 970), we measured the relative numbers of these macrophage subpopulations. There were more activated macrophages (epithelioid cells) associated with the increased granuloma fraction in the B10.BR mice than in the Balb/k. However, similar numbers of newly recruited peripheral macrophages were found in both Balb/k and B10.BR strains. This technique has shown qualitative as well as quantitative differences in the granulomatous inflammatory response in this murine model of tuberculosis in strains of mice with quite different antibody repertoires to mycobacterial antigens.

Galactose oxidation in the design of immunogenic vaccines

Potent immunological adjuvants are urgently required to complement recombinant and synthetic vaccines. However, it has not been possible to derive new principles for the design of vaccine adjuvants from knowledge of the mechanism of immunogenicity. Carbonyl-amino condensations, which are essential to the inductive interaction between antigen-presenting cells and T helper cells, were tested as a target for the enhancement of immune responses. Enzymic oxidation of cell-surface galactose to increase aminereactive carbonyl groups on murine lymphocytes and antigen-presenting cells provided a potent, noninflammatory method of enhancing the immunogenicity of viral, bacterial, and protozoal subunit vaccines in mice.