Chemically synthesized ubiquitin extension proteins detect distinct catalytic capacities of deubiquitinating enzymes

We have used solid-phase chemistry to synthesize proteins equivalent to a human ubiquitin precursor (ubiquitin-52-amino-acid ribosomal protein fusion; UBICEP52) and representative of isopeptide-linked ubiquitin-protein conjugates [ubiquitin-(epsilonN)-lysine]; these proteins were precisely cleaved by a purified recombinant Drosophila deubiquitinating enzyme (DUB), UCH-D. Along with the previously synthesized ubiquitin-(alphaN)-valine, these synthetic proteins were used as substrates to assess the catalytic capacities of a number of diverse DUBs expressed in Escherichia coli: human HAUSP; mouse Unp; and yeast Ubps 1p, 2p, 3p, 6p, 11p, and 15p and Yuh1p. Distinct specificities of these enzymes were detected; notably, in addition to UCH-D, isopeptidase activity [ubiquitin-(epsilonN)-lysine cleavage] was only associated with Yuh1p, Unp, Ubp1p, and Ubp2p. Additionally, human placental 26S proteasomes were only able to cleave UBICEP52 and ubiquitin-(epsilonN)-lysine, suggesting that 26S proteasome-associated DUBs are class II-like. This work demonstrates that the synthetic approach offers an alternative to recombinant methods for the production of small proteins in vitro.

Aggregation of RANTES is responsible for its inflammatory properties. Characterization of nonaggregating, noninflammatory RANTES mutants

The biology of RANTES (regulated on activation normal T cell expressed) aggregation has been investigated using RANTES and disaggregated variants, enabling comparison of aggregated, tetrameric, and dimeric RANTES forms. Disaggregated variants retain their G(i)-type G protein-coupled receptor-mediated biological activities. A correlation between RANTES aggregation and cellular activation has been demonstrated. Aggregated RANTES, but not disaggregated RANTES, activates human T cells, monocytes, and neutrophils. Dimeric RANTES has lost its cellular activating activity, rendering it noninflammatory. Macrophage inflammatory protein 1alpha, macrophage inflammatory protein-1beta, and erythrocytes are potent natural antagonists of aggregated RANTES-induced cellular activation. There is a clear difference in the signaling properties of aggregated and disaggregated RANTES forms, separating the dual signaling pathways of RANTES and the enhancing and suppressive effects of RANTES on human immunodeficiency virus infection. Disaggregated RANTES will be a valuable tool to explore the biology of RANTES action in human immunodeficiency virus infection and in inflammatory disease.

Manipulation of cholesterol and cholesteryl ester synthesis has multiple effects on the metabolism of apolipoprotein B and the secretion of very-low-density lipoprotein by primary hepatocyte cultures

Inhibition of esterified and non-esterified cholesterol synthesis by lovastatin in primary rat hepatocytes suppressed the net synthesis and very-low-density lipoprotein (VLDL) secretion of apolipoprotein B (apoB)-48 and apoB-100. Lovastatin did not alter the rates of apoB-48 and apoB-100 post-translational degradation. 25-Hydroxycholesterol, which inhibited non-esterified cholesterol synthesis but increased the synthesis of cholesteryl ester, showed differential effects on the metabolism of apoB-48 and apoB-100. Whereas the secretion of apoB-48 VLDL was suppressed there was no effect on the secretion of apoB-100 VLDL. The post-translational degradation of apoB-48, but not of apoB-100, was enhanced by 25-hydroxycholesterol. The net synthesis rates of apoB-48 and apoB-100 were unaffected by 25-hydroxycholesterol. The inhibitory effect of lovastatin alone on the net synthesis of apoB-48 and apoB-100 was reversed by the simultaneous presence of 25-hydroxycholesterol, suggesting a role for newly synthesised cholesteryl ester. Prevention of the reversal effect by the acyl-CoA: cholesterol acyltransferase (ACAT) inhibitor YM 17E supported this interpretation. In the presence of lovastatin, restoration of the net synthesis of apoB by 25-hydroxycholesterol was not accompanied by an increased VLDL output of apoB-48 and apoB-100. However, under these conditions there was an increased post-translational degradation of apoB-48 and apoB-100. These results suggest that interference with intracellular cholesterol and cholesteryl ester metabolism interrupts VLDL assembly at sites of both apoB net synthesis and post-translational degradation.

Simultaneous distributed strain and temperature measurement

Brillouin-scattering-based sensors are capable of measuring either the strain or the temperature along the length of an optical fiber in a distributed fashion through measurement of the Brillouin-frequency shift. The cross sensitivity of the frequency shift to these two parameters makes it impossible to differentiate between them by measurement of the frequency shift alone. We report on a new technique that permits the simultaneous measurement of strain and temperature to resolutions of +/-178 microepsilon and +/-3.9 degrees C at a spatial resolution of 3.5 m by incorporation of the Brillouin-loss peak power with the conventional Brillouin-frequency measurement.

A hookworm allergen which strongly resembles calreticulin

Immmoglobulin E-rich plasma from patients from Papua New Guinea infected with Necator americanus has been used to probe an adult N. americanus cDNA library for the presence of hookworm allergens. Using this approach, one hookworm allergen has been identified as calreticulin, which was subsequently expressed in Escherichia coli. Little serological cross reactivity was seen between the recombinant calreticulins of this hookworm and its host. Prospective roles for hookworm calreticulin in the host-parasite relationship are discussed in depth.

Cu/Zn superoxide dismutase in excretory-secretory products of the human hookworm Necator americanus. An electron paramagnetic spectrometry study

EPR spectrometry was used to investigate the effect of excretory/secretory product from Necator americanus on superoxide radical anions generated by xanthine/xanthine oxidase as a measure of excretory/secretory product superoxide dismutase activity. Using 1,1',5,5'-dimethylpyrollidine-N-oxide (DMPO) as a superoxide spin-trapping agent a 12-line EPR spectrum characteristic of the DMPO-OOH adduct was observed to decrease in the presence of excretory/secretory product. Superoxide dismutase activity was proportional to excretory/secretory protein concentration, was inhibited with cyanide treatment and was progressively destroyed with increasing time of heat denaturation of excretory/secretory product. Using a purpose-built chamber the superoxide dismutase activity of excretory/secretory product from live worms in culture was shown to accumulate with time to a maximum at 4 h. The electron paramagnetic resonance spectrum obtained for the frozen excretory/secretory product of N. americanus recorded at 77 K is typical of Cu(II) in a protein matrix. The results are consistent with the presence of an active Cu/Zn superoxide dismutase in excretory/secretory product from N. americanus and demonstrate a method for the unequivocal determination of the fate of superoxide anions in the presence of live worms.

Microbiological and radioactive contamination from radioaerosol ventilation scanning: is there a problem?

Radioaerosol lung imaging may result in (a) microbiological contamination of nebulizer circuits (a potential hazard to patients if the circuit is re-used), and (b) radioaerosol contamination of the atmosphere (a hazard to staff, particularly if inhaled, ingested or both). Altogether, 138 circuits were assessed for bacteriological contamination, 93 of which had been used for ventilation perfusion studies and 45 for lung permeability studies in human immunodeficiency virus (HIV) positive patients. The circuits used for ventilation/perfusion (V/Q) studies were re-used over a period of 1-5 days. The mouthpiece and Y-piece were changed between patients. The circuits used for permeability studies were changed in toto for each patient. Organisms belonging to normal respiratory flora were isolated from the Y-piece, mouthpiece or both in 9 of 138 cases. An additional case (from one of the HIV-positive patients) demonstrated a growth of methicillin-resistant Staphylococcus. We also demonstrated bacteriological growth, most likely of patient origin, in circuit tubing in 11 cases at the end of the first day's use and 9 cases by day 5. None of the circuits used for HIV-positive cases were culture-positive. Airborne radioactive contamination was assessed during radioaerosol inhalation with and without an air extractor device (Nederman) during 40 ventilation studies. The 20 studies with air extraction showed a large decrease in room air contamination. Nebulizer circuits can, and occasionally do, become contaminated with patients' organisms; this represents a potential infection control hazard and therefore re-use is contraindicated. The use of an air extractor will significantly reduce airborne radioaerosol contamination.

Automated system for capture and detection of nucleic acids

A fully automated nucleic acid analysis system is described, which offers positive sample identification, improved sensitivity and reduced user interaction compared to conventional techniques. The system relies on the sequence-specific capture of DNA onto solid-phase particles, confirming product identity without the problems of interpretation and lack of sequence information inherent in gel-based analyses. The system can be used for sequence confirmation, mutation analysis and semiquantitative detection of PCR products.

Selection for neutralization resistance of the simian/human immunodeficiency virus SHIVSF33A variant in vivo by virtue of sequence changes in the extracellular envelope glycoprotein that modify N-linked glycosylation

We previously reported on the in vivo adaptation of an infectious molecular simian/human immunodeficiency virus (SHIV) clone, SHIVSF33, into a pathogenic biologic viral variant, designated SHIVSF33A. In the present study, we show that SHIVSF33A is resistant to neutralization by human immunodeficiency virus (HIV) and SHIV antisera. Multiple amino acid substitutions accumulated over time throughout the env gene of SHIVSF33A; some of them coincided with the acquisition of the neutralization resistance of the virus. Of interest are changes that resulted in the removal, repositioning, and addition of potential glycosylation sites within the V1, V2, and V3 regions of envelope gp120. To determine whether potential glycosylation changes within these principal neutralization domains of HIV type 1 formed the basis for the resistance to serum neutralization of SHIVSF33A, mutant viruses were generated on the backbone of parental SHIVSF33 and tested for their neutralization sensitivity. The mutations generated did not alter the in vitro replication kinetics or cytopathicity of the mutant viruses in T-cell lines. However, the removal of a potential glycosylation site in the V1 domain or the creation of such a site in the V3 domain did allow the virus to escape serum neutralization antibodies that recognized parental SHIVSF33. The combination of the V1 and V3 mutations conferred an additive effect on neutralization resistance over that of the single mutations. Taken together, these data suggest that (i) SHIV variants with changes in the Env SU can be selected in vivo primarily by virtue of their ability to escape neutralizing antibody recognition and (ii) carbohydrates play an important role in conferring neutralization escape, possibly by altering the structure of envelope gp120 or by shielding principal neutralization sites.

Upper extremity infections in patients with diabetes mellitus

Forty-five consecutive diabetic patients with 46 upper extremity infections who underwent surgical debridement were retrospectively reviewed. The infections involved the skin or subcutaneous tissue in 19 patients and the fascia, tendon, muscle, or bone in 27. Twenty-three infections (50%) required a single operation and 23 required more than 1. Eighteen infections (39%) required an amputation and there were 3 deaths directly related to an infection. Six of 7 infections in which anaerobic organisms were cultured culminated in amputation. Four patients were diagnosed with necrotizing fasciitis. Twenty-one cultures (46%) were polymicrobial. An increased rate of amputation was associated with deep infections below the subcutaneous tissue, renal failure, and infections with gram-negative, anaerobic, or polymicrobial cultures. An increased rate of repeat surgery and a prolonged hospitalization were associated with deep infection and polymicrobial infections.

Identification of amino acid residues critical for aggregation of human CC chemokines macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and RANTES. Characterization of active disaggregated chemokine variants

Human CC chemokines macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and RANTES (regulated on activation normal T cell expressed) self-associate to form high-molecular mass aggregates. To explore the biological significance of chemokine aggregation, nonaggregating variants were sought. The phenotypes of 105 hMIP-1alpha variants generated by systematic mutagenesis and expression in yeast were determined. hMIP-1alpha residues Asp26 and Glu66 were critical to the self-association process. Substitution at either residue resulted in the formation of essentially homogenous tetramers at 0.5 mg/ml. Substitution of identical or analogous residues in homologous positions in both hMIP-1beta and RANTES demonstrated that they were also critical to aggregation. Our analysis suggests that a single charged residue at either position 26 or 66 is insufficient to support extensive aggregation and that two charged residues must be present. Solution of the three-dimensional NMR structure of hMIP-1alpha has enabled comparison of these residues in hMIP-1beta and RANTES. Aggregated and disaggregated forms of hMIP-1alpha, hMIP-1beta, and RANTES generally have equivalent G-protein-coupled receptor-mediated biological potencies. We have therefore generated novel reagents to evaluate the role of hMIP-1alpha, hMIP-1beta, and RANTES aggregation in vitro and in vivo. The disaggregated chemokines retained their human immunodeficiency virus (HIV) inhibitory activities. Surprisingly, high concentrations of RANTES, but not disaggregated RANTES variants, enhanced infection of cells by both M- and T-tropic HIV isolates/strains. This observation has important implications for potential therapeutic uses of chemokines implying that disaggregated forms may be necessary for safe clinical investigation.

Critical review of GABA-ergic drugs in the treatment of schizophrenia

GABA-ergic medications may have a potential role in the treatment of schizophrenia. Laboratory evidence has generally supported the ability of gamma-aminobutyric acid (GABA) to reduce dopaminergic activity and has suggested that GABA may be effective in combating hypofrontality by acting on mesoprefrontocortical tracts in patients resistant to treatment with antipsychotic drugs. Although the results of clinical trials of several GABA-ergic compounds have been inconclusive because of methodologic limitations and drug toxicity, benzodiazepines and valproate seem to be associated with favorable treatment outcomes, especially when combined with typical antipsychotic agents. This study concludes that further investigation of the use of GABA in schizophrenia is likely to improve the understanding of the psychopathology of this illness and to expand our treatment alternatives. Also provided are suggestions to enhance the design of future studies, improve the potential for favorable treatment outcomes, and assist in predicting patients' responses to GABA-ergic medications.

Decreasing lengths of stay: the cost to the community

BACKGROUND

Patients who are discharged earlier from hospital frequently require support from professional and unpaid carers at home after discharge. Hospitals save money per patient by discharging earlier, but it is not known whether the costs to community services and unpaid caters outweigh the savings to the hospital.

METHODS

We prospectively studied the total costs, patient satisfaction, time off work and pain scores of 224 patients who underwent elective herniorrhaphy or laparoscopic cholecystectomy and who lived locally before and after re-engineering the elective surgical service. The components of the re-engineered surgical service were a peri-operative unit, pre-admission anaesthetic assessment based on self-reported questionnaires, day of surgery admissions, enhanced patient education, clinical pathways, and post-acute care.

RESULTS

The patients treated through the re-engineered surgical service had a significantly shorter length of stay (LOS) (mean LOS: 2.2 vs 3.2 days; P < 0.001) but neither they nor their carers required more time off work. Significant determinants of time off work were smoking, heavy lifting at work and a higher pain score at day 7. Patients treated through the re-engineered surgical service recorded significantly higher satisfaction with their treatment. The cost saving to the hospital outweighed the cost of increased services provided in the community, so that the overall cost of providing treatment was over $200 less per patient through the re-engineered service.

CONCLUSIONS

This study demonstrates that changes in care provision that result in shorter LOS and greater cost effectiveness may better meet patients' needs than existing systems.

Impact of a modern firefighting protective uniform on the incidence and severity of burn injuries in New York City firefighters

The New York City Fire Department (FDNY) is the largest fire department in the United States, with over 11,000 firefighters. In 1994, FDNY changed to a modern firefighting protective uniform. The major difference between traditional and modern uniforms is that modern uniforms include both protective over-coat and over-pant, whereas traditional uniforms include only the over-coat. Furthermore, modern uniforms are manufactured using improved thermal protective textiles that meet or exceed current National Fire Protection Association standards for structural firefighting. The purpose of this study was to determine the impact of the modern uniform on the incidence and severity of FDNY burn injuries. We also evaluated the incidence and severity of other non-burn injuries to determine whether there was serious adverse impact. The number of lower-extremity burns decreased by 85% when 2 years' experience while wearing the modern uniform was compared with 2 years while wearing the traditional uniform. Upper-extremity burns and head burns decreased by 65% and 40%, respectively. Severity indicators (days lost to medical leave, hospital admissions, and skin grafts) for lower- and upper-extremity burn injuries were all substantially reduced. This occurred without significant change in the incidence or severity of trunk burns, heat exhaustion, inhalation injuries (actually decreased), or cardiac events. The reduction in the incidence and severity of burn injuries, the major occupational injury affecting this workforce, has been so dramatic and without untoward effects that the introduction of the modern uniform must be characterized as a sentinel event in the history of firefighter health and safety.

Educating health educators: a survey of hospital staff completing a certificate in health education course

Health care professionals (nurses, a midwife, a physiotherapist and an occupational therapist) working in a large NHS Trust hospital who had completed the Certificate in Health Education with the support of their employer, were interviewed. The study objectives were to seek their views on the quality of the course, to determine the extent to which participants were able to apply their new found knowledge and skills in the care they provided to patients and the level of support received to allow them to do this. Barriers that prevented staff from routinely applying health education in their work were identified. The findings indicated that the majority found the course content to be good and relevant to their clinical work but they identified lack of time due to the pressure of routine clinical work as the main barrier to the promotion of health education in their clinical area.

Remarkable stabilization of zwitterionic intermediates may account for a billion-fold rate acceleration by thiamin diphosphate-dependent decarboxylases

When the E91D variant of apo-yeast pyruvate decarboxylase (EC 4.1.1. 1) is exposed to C2alpha-hydroxybenzylthiamin diphosphate, this putative intermediate is partitioned on the enzyme between release of the benzaldehyde product (as evidenced by regeneration of active enzyme) and dissociation of the proton at C2alpha to form the enamine-C2alpha-carbanion intermediate. While the pKa (the negative log of the acid dissociation constant) for this dissociation is approximately 15.4 in water, formation of the enamine at pH 6.0 on the enzyme indicates a >9 unit pKa suppression by the enzyme environment. The dramatic stabilization of this zwitterionic enamine intermediate at the active center is sufficient to account for as much as a 10(9)-fold rate acceleration on the enzyme. This "solvent" effect could be useful for achieving the bulk of the rate acceleration provided by the protein over and above that afforded by the coenzyme on all thiamin diphosphate-dependent 2-oxo acid decarboxylases.

Noncytopathic clearance of lymphocytic choriomeningitis virus from the hepatocyte

We have previously shown that interferon and tumor necrosis factor noncytopathically abolish hepatitis B virus (HBV) replication from the hepatocyte and kidney tubular epithelial cells in vivo. Here we show that a persistent lymphocytic choriomeningitis virus (LCMV) infection is cleared from the hepatocyte noncytopathically when the same cytokines are induced in the liver by antigen-nonspecific stimuli. These results indicate that, like HBV, LCMV is also susceptible to intracellular inactivation by cytokine-induced antiviral mechanisms that are operative in the hepatocyte. In contrast, LCMV is not cleared from intrahepatic nonparenchymal cells or splenocytes, indicating that, unlike the hepatocyte, these cells do not produce the factors required to inactivate LCMV. Antiviral mechanisms like these may have evolved to maintain the functional integrity of vital organs in the face of massive infection.

Relative effectiveness and cost-effectiveness of methods of androgen suppression in the treatment of advanced prostate cancer

OBJECTIVES

With 184,500 new cases and 39,200 deaths anticipated in 1998, prostate cancer is second only to lung cancer in cancer mortality for men. This report is a systematic review of the evidence from randomized controlled trials on the relative effectiveness of alternative strategies for androgen suppression as treatment of advanced prostate cancer. Three key issues are addressed: (1) the relative effectiveness of the available methods for monotherapy (orchiectomy, luteinizing hormone-releasing hormone [LHRH] agonists, and antiandrogens), (2) the effectiveness of combined androgen blockade compared to monotherapy, and (3) the effectiveness of immediate androgen suppression compared to androgen suppression deferred until clinical progression. Outcomes of interest are overall, cancer-specific, and progression-free survival; time to treatment failure; adverse effects; and quality of life. Two supplementary analyses were conducted for each key question: (1) meta-analysis of overall survival at 2 years (questions 1 and 2) and 5 years (questions 2 and 3), and (2) cost-effectiveness analysis.

SEARCH STRATEGY

The MEDLINE, CANCERLIT, and EMBASE databases were searched from 1966 to March 1998, and Current Contents to August 24, 1998, for the terms: leuprolide (Lupron); goserelin (Zoladex); buserelin (Suprefact); flutamide (Eulexin); nilutamide (Anandron, Nilandron); bicalutamide (Casodex); cyproterone acetate (Androcur); diethylstilbestrol (DES); and orchiectomy (castration, orchidectomy). The search was then limited to human studies indexed under the MeSH term "prostatic neoplasms" and by the UK Cochrane Center search strategy for randomized controlled trials. Total yield was 1,477 references.

SELECTION CRITERIA

We Reports of efficacy outcomes were limited to randomized controlled trials. Phase II studies that reported on withdrawals from therapy and all studies reporting on quality of life were also included.

DATA COLLECTION AND ANALYSIS

The systematic review used a prospectively designed protocol conducted by two independent reviewers, with disagreements resolved by consensus. The meta-analysis combined data on overall survival using a random effects model. The cost-effectiveness analysis used a decision analysis model of advanced prostate cancer with health states and transitions derived from the literature and estimates of effectiveness derived from the meta-analysis. The cost-effectiveness analysis is conducted from a societal perspective, consistent with the guidelines of the U.S. Public Health Service Panel on Cost-Effectiveness in Health and Medicine.

MAIN RESULTS

Survival after treatment with an LHRH agonist is equivalent to survival after orchiectomy. The available LHRH agonists are equally effective, and no LHRH agonist is superior to the other when adverse effects are considered. Survival may be somewhat lower with use of a nonsteroidal antiandrogen. There is no statistically significant difference in survival at 2 years between patients treated with combined androgen blockade or monotherapy. Meta-analysis of the limited data available shows a statistically significant difference in survival at 5 years that favors combined androgen blockade. However, the magnitude of this difference is of questionable clinical significance. For the subgroup of patients with good prognosis, there is no statistically significant difference in survival. Adverse effects leading to withdrawal from therapy occurred more often with combined androgen blockade. No evidence is yet available from randomized controlled trials of androgen suppression initiated at prostate-specific antigen (PSA) rise after definitive therapy for clinically localized disease. For patients who are newly diagnosed with locally advanced or asymptomatic metastatic disease, the evidence is insufficient to determine whether primary androgen suppression initiated at diagnosis improves outcomes. (ABSTRACT TRUNCATED)

Necator americanus (human hookworm) aspartyl proteinases and digestion of skin macromolecules during skin penetration

The infective larvae of Necator americanus were shown to secrete all mechanistic classes of proteolytic enzymes with two overall pH optima of 6.5 and 8.5 using fluorescein isothiocyanate-labeled casein as the substrate. Since infective larvae are obligate skin penetrators, the effect of each of these enzyme classes against macromolecules derived from human skin was examined. Larval secretions were shown to degrade collagen types I, III, IV, and V, fibronectin, laminin, and elastin. All the skin macromolecules tested were hydrolyzed by aspartyl proteinase activity, which was inhibitable by pepstatin A. Collagen and elastin was also hydrolyzed by metalloproteinase activity, while the serine proteinase activity hydrolyzed only elastin. As a consequence of these experiments, the effect of proteinase inhibitors on the penetration of live larvae through hamster skin was tested. Larval penetration was significantly inhibited only by pepstatin A, confirming the importance of the aspartyl proteinase activity during the skin penetration process.

Structural monitoring by use of a Brillouin distributed sensor

The testing of a fiber-optic distributed-strain sensor attached to a simple structural member is reported. A Brillouin scattering-based sensor system was used to measure both tensile and compressive strains along the length of a cantilever beam subjected to various loads. The sensing fiber was attached to the beam in such a way that some sections experienced uniform strain, whereas others were subjected to a nonuniform strain distribution. A spatial resolution of 0.4 m was used, and a measurement precision of approximately +/-50 microepsilon was achieved.

Prenatal factors and adult mental and physical health

OBJECTIVE

To review research on prenatal influences on adult mental and physical health and draw implications for future directions in psychiatric research.

METHOD

Schizophrenia is selected as an example from mental health and cardiovascular disease as an example from physical health. For each of these disorders, empirical findings on prenatal influences are reviewed, and the methods used to demonstrate them are critiqued.

RESULTS

Research on prenatal antecedents of these conditions has proceeded in parallel: intriguing findings have related fetal growth restriction or fetal insult to adult health; similar types of causal pathways have been proposed to explain the relationships; and research has been plagued by similar limitations, including lack of precise prenatal exposure data and difficulty of controlling confounding. The prevailing view of disease causation, which is not well-suited to investigation of prenatal antecedents, impedes research in both fields. Yet, there has been little interchange between researchers in the 2 fields.

CONCLUSIONS

We propose a causal paradigm that could serve as a guide for future investigations on the prenatal antecedents of adult health and promote interchange between research on mental and physical health. The paradigm reflects current thinking in epidemiology by encompassing not only risk factors as traditionally conceived but also causal chains over time and causal influences at multiple levels of organization. Implications for the design of new research are illustrated with reference to an ongoing study.