Panoral dose assessment: a comparative report of methodologies.

National guidance from the Institute of Physics and Engineering in Medicine (IPEM Report 91) currently recommends that the patient dose for a panoral X-ray unit is measured as dose area product (DAP) replacing dose width product described in earlier guidance. An investigation identifying different methods available to carry out this measurement has been undertaken and errors in the methodologies analysed. It has been shown that there may be up to a 30 % variation in DAP measurement between methods. This paper recommends that where possible a DAP meter is used to measure the dose-area product from a panoral X-ray unit to give a direct DAP measurement. However, by using a solid-state dose measurement and film/ruler to calculate DAP the authors have established a conversion factor of 1.4. It is strongly recommended that wherever a DAP value is quoted the methodology used to obtain that value is also reported.

The effect of NIDCR R25 grant support on the curriculum and culture of a research non-intensive dental school.

Our objective was to evaluate changes in curriculum and culture within a research non-intensive dental school after implementation of programs supported by the NIH-NIDCR R25 Oral Health Research Curriculum Grant. We designed new curricular elements to foster an appreciation of research/discovery, an interest in academic/research careers, and application of biomedical/clinical advances to patient care. Funding was utilized to develop, implement, and assess a dedicated curricular track of continuous student research/scholarly activity throughout the four years of dental education. This track represented mandatory hours of didactic time exposing students to topics not traditionally included in dental curricula. Additionally, students were provided with customized flexible schedules to participate in elective "hands-on" mentored research/scholarly experiences at local, national, and international sites, including linkages to certificate, MS, and PhD programs. Funding was also used to support a wide array of faculty development activities that provided skill sets required to deliver integrated biomedical/clinical content, research-oriented evidence-based approaches to dental education, and translational case-based teaching methods emphasizing the application of new science/technologies to patient care. We measured changes in student, faculty, and institutional profiles/attitudes using traditional benchmarks, surveys, and focus groups. Comparisons were made between baseline data prior to R25 program initiation and data collected after years 3-4 of program implementation. Significant increases were demonstrated in: (1) student participation in research/scholarship, attendance at national meetings, research awards, publication of manuscripts, pursuit of advanced training/degrees, and expressions of interest in academic/research careers; (2) faculty participation in development activities, publication of manuscripts, and mentoring of students; and (3) increased institutional credibility within the university, supportive infrastructure for research/scholarship, and cultural expectations for academic excellence. Thus, we believe that the R25 programming changed the culture of our dental school, creating a supportive environment for research/scholarship, increasing academic productivity, and altering the attitudes of faculty/students.

Investigation of opportunistic pathogens in municipal drinking water under different supply and treatment regimes.

Changing regulations to lower disinfectant byproducts in drinking water is forcing utilities to switch disinfection from chlorine to monochloramine. It is generally unknown whether this will impact positively or negatively on the microbiological quality of drinking water. A utility in Florida, using water with relatively high organic carbon levels from deep wells in several wellfields, made the decision to change its disinfection regime from chlorine to chloramine in order to meet the new regulations. To assess the impacts of such a change on the microbiology of its water supplies, it undertook a number of studies before and after the change. In particular, the presence of the opportunistic pathogens Legionella and Mycobacterium, and also the composition of drinking-water biofilms, were examined. A preliminary synthesis and summary of these results are presented here. Legionella species were widely distributed in source waters and in the distribution system when chlorine was the disinfectant. In some samples they seemed to be among the dominant biofilm bacteria. Following the change to monochloramine, legionellae were not detected in the distribution system during several months of survey; however, they remained detectable at point of use, although with less species diversity. A variety of mycobacteria (21 types) were widely distributed in the distribution system when chlorine was the disinfectant, but these seemed to increase in dominance after chloramination was instituted. At point of use, only four species of mycobacteria were detected. Other changes occurring with chloramination included (a) an altered biofilm composition, (b) increased numbers of total coliforms and heterotrophs and (c) nitrification of water storage tanks. The results suggested that consideration should be given to the microbiological effects of changing disinfection regimes in drinking-water and distribution system biofilms.

A computational fluid dynamic and experimental study of an ozone contactor.

A computational fluid dynamic (CFD) model of an ozone contacting chamber in the Umgeni Water Wiggins Waterworks in Durban, South Africa, has been set up and verified by experimental tracer tests, as part of an investigation to optimise the control and disinfection efficiency of the contactor. The effect of gas injection was modelled by increasing the turbulent intensity at the reactor inlet. Experimental tracer responses which were used as partial verification of the model correspond very closely to model predictions.

Optimization of scanning parameters for CT colonography.

To determine the optimal collimation, pitch and reconstruction interval for CT colonography, 10 spherical polyps between 1 mm and 10 mm diameter and made of tissue equivalent material with a CT number of 40 Hounsfield units (HU) were placed in the colon of an anthropomorphic phantom. The phantom was scanned at slice thicknesses of 3 mm, 5 mm and 7 mm and pitches of 1.0, 1.3, 1.5, 1.7 and 2.0 on an IGE Hispeed advantage system. Images were reconstructed for each scanning parameter at the minimum intervals allowed along the z-axis. The optimum scanning protocol was assessed by measuring maximum contrast between the polyp and air, sensitivity for detection of each polyp along the z-axis, and relative radiation dose. In addition, images were reviewed separately by two radiologists who graded polyp conspicuity as: 0, not seen; 1, faintly seen; 2, well seen. It was found that varying the scanning parameters caused a marked alteration in the maximum contrast between each polyp and air. For example, for the 5 mm polyp, the range of contrasts from best to worst case was 910-490 HU. It was noted that with contrasts of less than 500 HU, polyps were only faintly seen. A slice thickness of 3 mm with a pitch of 2 offers optimal polyp conspicuity with a relatively low radiation dose, we conclude that scanning parameters can be optimized for threshold contrast, radiation dose and subjective conspicuity. We propose an optimal parameter of 3 mm slice thickness and pitch 2.

Replication of dengue virus type 2 in human monocyte-derived macrophages: comparisons of isolates and recombinant viruses with substitutions at amino acid 390 in the envelope glycoprotein.

The severity of dengue virus infection ranges from mild fever to dengue hemorrhagic fever and shock syndrome. The association of disease severity with virus replication in monocyte-derived macrophages (MDMs) was examined for dengue virus type 2 (DEN-2) isolates from Asia or America. Additionally, we constructed DEN-2 recombinant viruses with substitutions at residue 390 in the envelope glycoprotein (E390) because this residue is linked with the region of virus origin. Comparisons of virus yields of 3 isolates failed to show a correlation with clinical disease. However, the American strain did not replicate as well as the 2 Asian strains. For the recombinant viruses, substitution of Asn (Asian) at E390 with Asp (American) resulted in decreased ability to replicate in MDMs. These results are consistent with the proposal that the lack of association of native American DEN-2 strains with severe disease is linked to reduced ability to replicate in MDMs, and that Asp at E390 may contribute to this reduction.

Mutagenesis of the Dengue virus type 2 NS3 protein within and outside helicase motifs: effects on enzyme activity and virus replication.

The protein NS3 of Dengue virus type 2 (DEN-2) is the second largest nonstructural protein specified by the virus and is known to possess multiple enzymatic activities, including a serine proteinase located in the N-terminal region and an NTPase-helicase in the remaining 70% of the protein. The latter region has seven conserved helicase motifs found in all members of the family Flaviviridae. DEN-2 NS3 lacking the proteinase region was synthesized as a fusion protein with glutathione S-transferase in Escherichia coli. The effects of 10 mutations on ATPase and RNA helicase activity were examined. Residues at four sites within enzyme motifs I, II, and VI were substituted, and six sites outside motifs were altered by clustered charged-to-alanine mutagenesis. The mutations were also tested for their effects on virus replication by incorporation into genomic-length cDNA. Two mutations, both in motif I (G198A and K199A) abolished both ATPase and helicase activity. Two further mutations, one in motif VI (R457A,R458A) and the other a clustered charged-to-alanine substitution at R(376)KNGK(380), abolished helicase activity only. No virus was detected for any mutation which prevented helicase activity, demonstrating the requirement of this enzyme for virus replication. The remaining six mutations resulted in various levels of enzyme activities, and four permitted virus replication. For the two nonreplicating viruses encoding clustered changes at R(184)KR(186) and D(436)GEE(439), we propose that the substituted residues are surface located and that the viruses are defective through altered interaction of NS3 with other components of the viral replication complex. Two of the replicating viruses displayed a temperature-sensitive phenotype. One contained a clustered mutation at D(334)EE(336) and grew too poorly for further characterization. However, virus with an M283F substitution in motif II was examined in a temperature shift experiment (33 to 37 degrees C) and showed reduced RNA synthesis at the higher temperature.

Lack of secondary hyperalgesia and central sensitization in an acute sheep model.

BACKGROUND AND OBJECTIVES: We aimed to determine the following in an experimental acute pain model in sheep: (1) whether multimodal analgesia with intravenous fentanyl and ketorolac was more effective than fentanyl alone; (2) whether secondary hyperalgesia (central sensitization) occurred in adjacent (foreleg) dermatomes after thoracic surgery; (3) whether ketorolac used preemptively influenced the development of secondary hyperalgesia after surgery. METHODS: Changes in primary nociception were measured by increases to tolerated pressure, applied to the foreleg by a blunt pin, before foreleg withdrawal occurred. Changes to breath-to-breath interval and estimated end-tidal CO2 were used as indices of respiratory effects. Study 1 (n = 6) compared the paired responses to acute nociception after ketorolac (90 mg) or saline (control) pretreatment, followed by fentanyl (graded, 0 mg to 1.5 mg). Study 2 (n = 6) used a cross-over of ketorolac (90 mg) or saline (control) 24 hours and 1 hour, respectively, before a standardized thoracotomy incision, followed by antinociceptive testing with ketorolac (90 mg) and fentanyl (0.6 mg) daily over 4 days. RESULTS: In study 1, fentanyl produced naloxone-antagonizable antinociception and respiratory depression. Ketorolac did not affect fentanyl antinociception, except for prolonging antinociception at the highest dose; it did not affect the respiratory effects. In study 2, preemptive ketorolac had no effect on the postoperative antinociceptive or respiratory effects of fentanyl. The pharmacokinetics of fentanyl were unaltered by ketorolac. CONCLUSIONS: The results obtained in this acute pain model found no significant evidence of a fentanyl-ketorolac interaction, of central sensitization as shown by secondary hyperalgesia, or of a preemptive analgesic effect.

Evaluation of a MOSFET radiation sensor for the measurement of entrance surface dose in diagnostic radiology.

A patient dosimetry system using MOSFET technology (Thomson and Neilson Electronics Ltd, Canada) is evaluated for entrance surface dose measurements in diagnostic radiology. The system sensitivity for the standard MOSFET detector coupled to a high sensitivity bias supply was measured to be 1 mV mGy-1. Response of a new high sensitivity dosemeter was measured to be 3 mV mGy-1. The minimum detectable entrance surface dose at which a single measurement can be made with less than 25% total uncertainty at the 95% confidence level was estimated to be 4 mGy for the standard dosemeter and 1.5 mGy for the new high sensitivity dosemeter. The dosemeters were found to be linear with absorbed dose in air, linear with dose rate and reproducible, although they showed some energy dependence across the diagnostic energy range. The system is also compared with thermoluminescent dosimetry (TLD) as a tool for the measurement of entrance surface dose in diagnostic radiology. MOSFET detectors are considered to have advantages over TLD dosemeters with the instant readout of entrance surface dose. These dosemeters do have the disadvantage that they are visible in radiographs, they have a finite shelf life and can only accumulate absorbed dose up to a limiting value after which the dosemeters can no longer be used.

Growth restriction of dengue virus type 2 by site-specific mutagenesis of virus-encoded glycoproteins.

The three flavivirus glycoproteins prM, E and NS1 are formed by post-translational cleavage and are glycosylated by the addition of N-linked glycans. NS1 may form homodimers, whereas E may form homodimers, homotrimers or heterodimers (prM-E). Modification of these processes by mutagenesis of the proteins has the potential to generate viruses that are restricted in growth and are possible vaccine candidates. Using an SV40-based expression system, we previously analysed dimerization and secretion of the NS1 protein of dengue virus type 2 (DEN-2) with mutations in the conserved Cys residues, or within hydrophilic or hydrophobic regions, or at glycosylation sites. In this study, mutations which reduce cleavage at the DEN-2 prM/E signalase cleavage site are described. On the basis of earlier and current results with transient expression, six mutations which reduced NS1 dimerization and two mutations which inhibited prM/E cleavage were analysed individually for their effects on virus growth using a genomic length cDNA clone. Two viruses were obtained that showed reduced growth in cell culture and attenuation of neurovirulence when inoculated into 3-day-old mice. One of these viruses encoded NS1 that lacked the second glycosylation site, the other encoded a Ser --> Ile change at the -3 position of the prM/E cleavage site. A third virus encoding a mutation in NS1 within a hydrophilic region grew as well as the parental virus. No virus was detected for the remaining five mutations.

Cardiovascular and central nervous system effects of intravenous levobupivacaine and bupivacaine in sheep.

UNLABELLED: Commercially available bupivacaine is an equimolar mixture of R(+)- and S(-)-bupivacaine. S(-)-bupivacaine (i.e., levobupivacaine) is currently undergoing preclinical evaluation. Cross-over studies with i.v. levobupivacaine and bupivacaine were conducted in two groups of seven conscious sheep. Doses were chosen to avoid convulsions (smaller dose 6.25-37.5 mg/min) or to be potentially toxic (larger dose 75-200 mg/3 min). In subconvulsive doses, both drugs produced similar time- and dose-dependent depression of left ventricular systolic contractility (dP/dt(max)). Convulsions occurred consistently with > or = 75 mg of bupivacaine and > or = 100 mg of levobupivacaine, producing an abrupt reversal of dP/dt(max) depression. Subconvulsive doses produced minor cardiovascular effects on heart rate and blood pressure, whereas both were increased by convulsions. Cardiac output and myocardial blood flow were decreased with larger doses of both drugs. Doses > 75 mg of bupivacaine or > 100 mg of levobupivacaine induced QRS widening and ventricular arrhythmias, but significantly fewer and less deleterious arrhythmias were induced by levobupivacaine. Three animals died after 150, 150, and 200 mg of bupivacaine from the sudden onset of ventricular fibrillation. These doses of levobupivacaine produced nonfatal arrhythmias that automatically returned to sinus rhythm. We conclude that levobupivacaine could offer a greater margin of clinical safety than bupivacaine. IMPLICATIONS: Levobupivacaine comprises 50% of commercially available bupivacaine and is being considered for use in its own right. Local anesthetics can cause toxicity to the cardiovascular and central nervous systems. As a part of a preclinical evaluation of levobupivacaine, this study compared the toxic effects of levobupivacaine and bupivacaine in sheep.

Systemic and regional pharmacokinetics of levobupivacaine and bupivacaine enantiomers in sheep.

UNLABELLED: Commercially available bupivacaine is an equimolar mixture of R(+)- and S(-)-bupivacaine. S(-)-bupivacaine (levobupivacaine) is the subject of current clinical evaluation. We conducted partial cross-over systemic and regional pharmacokinetic studies of i.v. bupivacaine (12.5-200 mg) and levobupivacaine (6.25-200 mg) in ewes. Enantiospecific analysis of blood drug concentration-time data and of regional myocardial and brain drug mass balance data indicated that (a) there was a higher mean total body clearance of R(+)-bupivacaine than of S(-)-bupivacaine (as previously reported); (b) there were no differences in the systemic pharmacokinetics of S(-)-bupivacaine whether administered alone or as a component of bupivacaine; (c) there was no evidence of dose-dependent pharmacokinetics with either enantiomer; (d) for both enantiomers, mean calculated myocardial tissue concentrations of 1%-4% dose occurred between 3 and 5 min. Mean brain concentrations of 0.2%-1% dose occurred between 2 and 4 min after the administration of bupivacaine but between 4 and 5 min after the administration of levobupivacaine. There was no evidence that systemic toxicity induced by these local anesthetics significantly modified their pharmacokinetics, and there was no evidence of an enantiomer-enantiomer pharmacokinetic interaction for bupivacaine. IMPLICATIONS: Levobupivacaine comprises 50% of commercially available bupivacaine and is being considered for use in its own right. As a part of its preclinical evaluation, this study considered whether levobupivacaine behaved kinetically in the body in the same way as when administered as a component of bupivacaine.

Identification of a major determinant of mouse neurovirulence of dengue virus type 2 using stably cloned genomic-length cDNA.

A genomic-length cDNA clone corresponding to the RNA of dengue virus type 2 (DEN-2) New Guinea C strain (NGC) was constructed in a low copy number vector. The cloned cDNA was stably propagated in Escherichia coil and designated pDVWS501. RNA transcripts produced in vitro from the cDNA using T7 RNA polymerase yielded infectious virus (MON501) upon electroporation into BHK-21 cells. When compared with parental NGC virus, MON501 replicated to similar levels in Aedes albopictus C6/36 cells and showed similar neurovirulence in suckling mice. In contrast, a second genomic-length cDNA clone (pDVWS310) used as an intermediate in the construction of pDVWS501 produced virus (MON310) that replicated well in C6/36 cells but was not neurovirulent in mice. MON310 contained the prM and E genes of the non-neurovirulent PUO-218 strain in an NGC background. There were seven amino acid differences between the prM and E proteins of MON310 and MON501. The differences were generally conservative, with the exception of E residue 126, which was Glu in MON310 and Lys in MON501. To examine the role of this residue in mouse neurovirulence, substitutions of Glu --> Lys and Lys --> Glu were made in MON310 and MON501, respectively. The properties of these mutants clearly demonstrated that Lys at E residue 126 is a major determinant of DEN-2 mouse neurovirulence.

Noisy breathing in children: history and presentation hold many clues to the cause.

Evaluation of noisy breathing in children begins with careful history taking and physical examination focusing on the patient's age and the character of the noisy breathing. Establishing whether stridor, wheezing, rales, or a combination of these is present and whether the problem is acute or chronic can rule out certain disorders and suggest others. From this point, further diagnostic testing can be pursued and appropriate therapy initiated.

Glycosylation mutants of dengue virus NS1 protein.

The non-structural glycoprotein NS1 of dengue virus type 2 contains sites for N-linked glycosylation at Asn-130 and Asn-207. NS1 synthesized in infected cells is glycosylated at both locations. We have now examined the dimerization and secretion of NS1 lacking one or both of these sites by transient expression of mutagenized cDNA inserted into a simian virus 40-based vector. Immunoblotting and radioimmunoprecipitation were used to detect NS1 associated with transfected cells and in the extracellular medium. Elimination of one or both glycosylation sites did not abolish dimerization and secretion of NS1. However, NS1 lacking Asn-207 showed reduced dimer stability and secretion. Treatment of secreted NS1 with endoglycosidase H demonstrated that complex glycans were attached at Asn-130 and high-mannose glycans at Asn-207.

The effects of site-directed mutagenesis on the dimerization and secretion of the NS1 protein specified by dengue virus.

cDNA of dengue virus type 2 encoding the glycoprotein NS1 was transiently expressed in COS cells using an SV40-based vector. To test the importance of selected regions of the protein in dimer formation, constructs were prepared which encoded amino acid changes at specific locations. Six of the 12 Cys residues in the NS1 protein were individually changed to Ala. Two amino acids in each of three hydrophilic and two hydrophobic areas of the protein were also changed to Ala. The ability of these 11 mutant proteins to form dimers, the sensitivity of the dimers to dissociation by heat, and the secretion of the mutant proteins from transfected cells were investigated by immunoblotting, immunoprecipitation, and indirect immunofluorescence. The results demonstrated that the carboxy terminal end of the protein is important in dimer formation. In particular, the substitution of Ala for any one of the last three Cys residues, which are located within the carboxy terminal forty amino acids of the protein, prevented dimer formation. Only the proteins which formed dimers were detected at the cell surface and in the extracellular medium. No monomers were secreted.

Anti-oxidized low-density lipoprotein antibodies in patients with coronary heart disease and normal healthy volunteers.

We have developed a solid-phase enzyme immunoassay for anti-oxidized low-density lipoprotein antibodies. Most sera showed some degree of non-specific binding to plates coated with oxidized low-density lipoprotein and the autoantibodies to oxidized low-density lipoprotein often appeared to have a relatively low affinity. To differentiate between specific and non-specific binding each sample was tested untreated and after absorption with oxidized low-density lipoprotein. The optical densities obtained with dilutions of the absorbed sample were considered to reflect non-specific binding and were subtracted from values obtained with identical dilutions of the unabsorbed sample, to yield corrected values from which the concentrations of anti-oxidized low-density lipoprotein antibody were calculated. Similar absorptions with native low-density lipoprotein and oxidized human serum albumin failed to induce a significant reduction in binding to immobilized oxidized low-density lipoprotein proving that the antibodies measured by this assay are primarily specific for oxidized low-density lipoprotein. We studied sera from two groups of individuals: (1) 33 subjects submitted to coronary angiography and split into two subgroups depending on the degree of coronary stenosis and (2) 64 healthy individuals also split into two subgroups according to lipid levels. Anti-oxidized low-density lipoprotein antibodies were detected both in patients and healthy individuals. Higher levels were detected in patients with moderate coronary disease and hyperlipemic healthy individuals, but the differences between patients and healthy volunteers or between their respective subgroups did not reach statistical significance. Our results suggest that autoantibodies to oxidized low-density lipoprotein are relatively frequent in both symptomatic and asymptomatic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent diet and breast cancer in Utah.

A population-based case-control study was conducted to assess the association between breast cancer risk, body mass index (BMI) and adolescent dietary fat and fiber consumption. Data were collected in Utah from white female cases (N = 172) and controls (N = 190) between the ages of 20 and 54 years. Odds ratios (OR) and 95% test-based confidence intervals (CI) were determined by multiple-logistic regression analysis controlling for age, education, age at menarche, and age at first pregnancy. Menopausal status was identified as an effect modifier, therefore, separate analyses were performed for pre and postmenopausal groups. An elevated risk (OR = 2.9 for highest quartile versus lowest, CI = 1.1-8.1) was associated with a larger BMI at age 12 in premenopausal women; a larger adult BMI lowered the odds ratio (OR = 0.4, CI = 0.2-1.0 for highest quartile versus lowest) in premenopausal women; BMI did not alter risk in postmenopausal women. Although not statistically significant, high fat intake consistently lowered the odds ratios below 1.0 in premenopausal women in the upper three quartiles compared to the lowest fat intake referent quartile (OR = 0.7, CI = 0.2-2.1 for highest versus lowest quartile) but was inconsistent in postmenopausal women (OR = 0.7, CI = 0.2-2.7 for highest versus lowest quartile). When fat intake was assessed by its component parts, fat from milk, cheese and yogurt reduced the odds ratios in both premenopausal (OR = 0.4, CI = 0.1-1.1 for highest versus lowest quartile) and postmenopausal women (OR = 0.2, CI = 0.0-0.8). In postmenopausal women, high fiber intake produced elevated odds ratios in all three upper quartiles (OR = 6.6, CI = 1.5-29.6 for highest versus lowest quartile), while fiber from grains resulted in a decreased risk in both premenopausal (OR = 0.2, 95% CI = 0.2-0.7 for highest versus lowest quartile) and postmenopausal women (OR = 0.7, 95% CI = 0.3-2.0). The possibility of biased estimates from low response rates (cases = 60%, controls = 61%), potential recall bias, and some lack of precision in the dietary instrument should be considered. It appears from these analyses that the relation of breast cancer to dietary intake, especially during adolescent years, is not clear, and that risk associated with fat or fiber intake may be affected by the nutrient source.

Steady-state levels of uroporphyrinogen decarboxylase mRNA in lymphoblastoid cell lines from patients with familial porphyria cutanea tarda and their relatives.

Familial porphyria cutanea tarda (PCT) results from a generalized deficiency of uroporphyrinogen decarboxylase (URO-D) activity. The molecular defect responsible for this disorder has not been characterized. To determine whether decreased levels of URO-D mRNA are responsible for subnormal URO-D activity, steady-state levels of URO-D mRNA in lymphoblastoid cells were determined. Northern blots were hybridized with a URO-D cDNA probe and quantified by densitometry. No difference in the levels of URO-D mRNA was detected between affected individuals and their normal relatives. Thus, the deficiency of URO-D activity in two familial PCT pedigrees characterized here does not arise from a deficiency of URO-D mRNA.

Suppression of natural killer cell activity in humans by radiation from solarium lamps depleted of UVB.

Previous studies have shown that ultraviolet radiation (UVR) from solarium lamps suppressed natural killer (NK) cell activity in the blood and that sunscreen lotions offered no protection against this effect. In the present study we tried to determine whether the effects on NK cell activity were caused by the UVB or the UVA components of radiation from solarium lamps by filtering out UVB with Mylar sheeting. Groups of 10 normal subjects were either left untreated or exposed for 30 min on 12 consecutive days to radiation that was filtered or not filtered through a 0.1 mm thick Mylar sheeting. NK cell activity was depressed in the group exposed to solarium radiation and this was not prevented by filtration through Mylar. The latter procedure, however, appeared to prevent changes in blood lymphocyte subsets that are induced by solarium radiation as well as the reduction in Langerhans cell numbers in skin biopsies taken after exposure to solarium radiation. Suppression of NK cell activity was evident up to 14 days after cessation of UVR exposure. This would be consistent with the replacement of NK cells from bone marrow that had been damaged as a result of direct effects of UVA on NK cells in the microcirculation of the skin or else indicate functional suppression of NK cells by suppressor cells induced by UVR as postulated for UVR-induced suppression of delayed hypersensitivity responses in murine models. These studies suggest that UVA may be important in the induction of certain effects on the immune system in human subjects. Further studies are required to assess the implications of these findings with respect to induction of neoplasia and the design of sunscreens effective against UVA.