Assessment of Antibiotic Prescriptions for Lyme Disease After Modification of Reporting Language for Positive Screening Test Results

This quality improvement study assesses whether revision of positive Lyme disease test result text was associated with decreases in the frequency of antibiotic prescriptions for patients without confirmatory results.

Using electronic health records to identify candidates for human immunodeficiency virus pre-exposure prophylaxis: An application of super learning to risk prediction when the outcome is rare

Human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) protects high risk patients from becoming infected with HIV. Clinicians need help to identify candidates for PrEP based on information routinely collected in electronic health records (EHRs). The greatest statistical challenge in developing a risk prediction model is that acquisition is extremely rare.

METHODS

Data consisted of 180 covariates (demographic, diagnoses, treatments, prescriptions) extracted from records on 399 385 patient (150 cases) seen at Atrius Health (2007-2015), a clinical network in Massachusetts. Super learner is an ensemble machine learning algorithm that uses k-fold cross validation to evaluate and combine predictions from a collection of algorithms. We trained 42 variants of sophisticated algorithms, using different sampling schemes that more evenly balanced the ratio of cases to controls. We compared super learner's cross validated area under the receiver operating curve (cv-AUC) with that of each individual algorithm.

RESULTS

The least absolute shrinkage and selection operator (lasso) using a 1:20 class ratio outperformed the super learner (cv-AUC = 0.86 vs 0.84). A traditional logistic regression model restricted to 23 clinician-selected main terms was slightly inferior (cv-AUC = 0.81).

CONCLUSION

Machine learning was successful at developing a model to predict 1-year risk of acquiring HIV based on a physician-curated set of predictors extracted from EHRs.

Development and validation of an automated HIV prediction algorithm to identify candidates for pre-exposure prophylaxis: a modelling study

BACKGROUND

HIV pre-exposure prophylaxis (PrEP) is effective but underused, in part because clinicians do not have the tools to identify PrEP candidates. We developed and validated an automated prediction algorithm that uses electronic health record (EHR) data to identify individuals at increased risk for HIV acquisition.

METHODS

We used machine learning algorithms to predict incident HIV infections with 180 potential predictors of HIV risk drawn from EHR data from 2007-15 at Atrius Health, an ambulatory group practice in Massachusetts, USA. We included EHRs of all patients aged 15 years or older with at least one clinical encounter during 2007-15. We used ten-fold cross-validated area under the receiver operating characteristic curve (cv-AUC) with 95% CIs to assess the model's performance at identifying individuals with incident HIV and patients independently prescribed PrEP by clinicians. The best-performing model was validated prospectively with 2016 data from Atrius Health and externally with 2011-16 data from Fenway Health, a community health centre specialising in sexual health care in Boston (MA, USA). We calculated HIV risk scores (ie, probability of an incident HIV diagnosis) for every HIV-uninfected patient not on PrEP during 2007-15 at Atrius Health and assessed the distribution of scores for thresholds to determine possible candidates for PrEP in the three study cohorts.

FINDINGS

We included 1 155 966 Atrius Health patients from 2007-15 (150 [<0·1%] patients with incident HIV) in our development cohort, 537 257 Atrius Health patients in 2016 (16 [<0·1%] with incident HIV) in our prospective validation cohort, and 33 404 Fenway Health patients from 2011-16 (423 [1·3%] with incident HIV) in our external validation cohort. The best-performing algorithm was obtained with least absolute shrinkage and selection operator (LASSO) and had a cv-AUC of 0·86 (95% CI 0·82-0·90) for identification of incident HIV infections in the development cohort, 0·91 (0·81-1·00) on prospective validation, and 0·77 (0·74-0·79) on external validation. The LASSO model successfully identified patients independently prescribed PrEP by clinicians at Atrius Health in 2016 (cv-AUC 0·93, 95% CI 0·90-0·96) or Fenway Health (0·79, 0·78-0·80). HIV risk scores increased steeply at the 98th percentile. Using this score as a threshold, we prospectively identified 9515 (1·8%) of 536 384 patients at Atrius Health in 2016 and 4385 (15·3%) of 28 702 Fenway Health patients as potential PrEP candidates.

INTERPRETATION

Automated algorithms can efficiently identify patients at increased risk for HIV acquisition. Integrating these models into EHRs to alert providers about patients who might benefit from PrEP could improve prescribing and prevent new HIV infections.

FUNDING

Harvard University Center for AIDS Research, Providence/Boston Center for AIDS Research, Rhode Island IDeA-CTR, the National Institute of Mental Health, and the US Centers for Disease Control and Prevention.

Temporal Patterns in Chlamydia Repeat Testing in Massachusetts

INTRODUCTION

National guidelines recommend test-of-cure for pregnant women and test-of-reinfection for all patients with chlamydia infections in order to interrupt transmission and prevent adverse sequelae for patients, partners, and newborns. Little is known about retesting and positivity rates, and whether they are changing over time, particularly in private sector practices.

METHODS

Electronic health record data on patients with chlamydia tests were extracted from three independent clinical practice groups serving ≅20% of the Massachusetts population. Records were extracted using the Electronic medical record Support for Public Health platform (esphealth.org). These data were analyzed for temporal trends in annual repeat testing rates by using generalized estimating equations after index positive chlamydia tests between 2010 and 2015 and for differences in intervals to first repeat tests among pregnant females, non-pregnant females, and males. Data extraction and analysis were performed during calendar years 2017 and 2018.

RESULTS

An index positive C. trachomatis result was identified for 972 pregnant female cases, 10,309 non-pregnant female cases, and 4,973 male cases. Test-of-cure 3-5 weeks after an index positive test occurred in 37% of pregnant females. Test-of-reinfection 8-16 weeks after an index positive test occurred in 39% of pregnant females, 18% of non-pregnant females, and 9% of males. There were no significant increases in test-of-cure or test-of-reinfection rates from 2010 to 2015. Among cases with repeat tests, 16% of pregnant females, 15% of non-pregnant females, and 16% of males had positive results.

CONCLUSIONS

Chlamydia test-of-cure and test-of-reinfection rates are low, with no evidence of improvement over time. There are substantial opportunities to improve adherence to chlamydia repeat testing recommendations.

Automated influenza-like illness reporting--an efficient adjunct to traditional sentinel surveillance

OBJECTIVES

We compared an electronic health record-based influenza-like illness (ILI) surveillance system with manual sentinel surveillance and virologic data to evaluate the utility of the automated system for routine ILI surveillance.

METHODS

We obtained weekly aggregate ILI reports from the Electronic medical record Support for Public Health (ESP) disease-detection and reporting system, which used an automated algorithm to identify ILI visits among a patient population of about 700,000 in Eastern Massachusetts. The percentage of total visits for ILI ("percent ILI") in ESP, percent ILI in the Massachusetts Department of Public Health's sentinel surveillance system, and percentage of laboratory specimens submitted to participating Massachusetts laboratories that tested positive for influenza were compared for the period October 2007-September 2011. We calculated Spearman's correlation coefficients and compared ESP and sentinel surveillance systems qualitatively, in terms of simplicity, flexibility, data quality, acceptability, timeliness, and usefulness.

RESULTS

ESP and sentinel surveillance percent ILI always peaked within one week of each other. There was 80% correlation between the two and 71%-73% correlation with laboratory data. Sentinel surveillance percent ILI was higher than ESP percent ILI during influenza seasons. The amplitude of variation in ESP percent ILI was greatest for 5- to 49-year-olds and typically peaked for the 5- to 24-year-old age group before the others.

CONCLUSIONS

The ESP system produces percent ILI data of similar quality to sentinel surveillance and offers the advantages of shifting disease reporting burden from clinicians to information systems, allowing tracking of disease by age group, facilitating efficient surveillance for very large populations, and producing consistent and timely reports.

Initial Antibiotic Choice in the Treatment of Group A Streptococcal Pharyngitis and Return Visit Rates

BACKGROUND

Our objectives were to describe the incidence of return visits for children with Group A Streptococcal (GAS) pharyngitis (ie, clinical treatment failure) and to assess whether initial treatment with amoxicillin or penicillin was associated with the rate of retreatment for GAS pharyngitis.

METHODS

This analysis was a retrospective cohort study of 5533 children 0-17 years from a multisite practice. Eligible visits (n = 6585) were associated with a positive test for GAS, receipt of antibiotics within 7 days, no allergies to penicillins or cephalosporins, and no codiagnoses requiring antibiotic treatment. Retreatment for GAS pharyngitis was defined as an index visit followed by another visit within 1-4 weeks. Five hundred episodes (250 treatment failures and 250 controls) were randomly selected for chart review to validate cases.

RESULTS

Amoxicillin or penicillin was the initial antibiotic treatment at 76.1% of visits, and retreatment for GAS pharyngitis occurred after 5.8% of initial visits. Children initially prescribed amoxicillin or penicillin had higher odds of retreatment of GAS pharyngitis even after adjusting for age, sex, symptoms, and community-level covariates such as race, income, and education (odds ratio, 1.51; 95% confidence interval, 1.07-2.13).

CONCLUSIONS

Retreatment for GAS pharyngitis was uncommon and associated with receipt of amoxicillin or penicillin, although the impact of GAS carriage is unknown. Recommendations for initial treatment of GAS pharyngitis should reflect both individual and societal considerations, including the potential impact on antibiotic resistance in the community.

Integrating clinical practice and public health surveillance using electronic medical record systems

Electronic medical record (EMR) systems have rich potential to improve integration between primary care and the public health system at the point of care. EMRs make it possible for clinicians to contribute timely, clinically detailed surveillance data to public health practitioners without changing their existing workflows or incurring extra work. New surveillance systems can extract raw data from providers' EMRs, analyze them for conditions of public health interest, and automatically communicate results to health departments. We describe a model EMR-based public health surveillance platform called Electronic Medical Record Support for Public Health (ESP). The ESP platform provides live, automated surveillance for notifiable diseases, influenza-like illness, and diabetes prevalence, care, and complications. Results are automatically transmitted to state health departments.

Integrating clinical practice and public health surveillance using electronic medical record systems

Electronic medical record (EMR) systems have rich potential to improve integration between primary care and the public health system at the point of care. EMRs make it possible for clinicians to contribute timely, clinically detailed surveillance data to public health practitioners without changing their existing workflows or incurring extra work. New surveillance systems can extract raw data from providers' EMRs, analyze them for conditions of public health interest, and automatically communicate results to health departments. The current paper describes a model EMR-based public health surveillance platform called Electronic Medical Record Support for Public Health (ESP). The ESP platform provides live, automated surveillance for notifiable diseases, influenza-like illness, and diabetes prevalence, care, and complications. Results are automatically transmitted to state health departments.

Evaluating real-time syndromic surveillance signals from ambulatory care data in four states

OBJECTIVES

We evaluated a real-time ambulatory care-based syndromic surveillance system in four metropolitan areas of the United States.

METHODS

Health-care organizations and health departments in California, Massachusetts, Minnesota, and Texas participated during 2007-2008. Syndromes were defined using International Classification of Diseases, Ninth Revision diagnostic codes in electronic medical records. Health-care organizations transmitted daily counts of new episodes of illness by syndrome, date, and patient zip code. A space-time permutation scan statistic was used to detect unusual clustering. Health departments followed up on e-mailed alerts. Distinct sets of related alerts ("signals") were compared with known outbreaks or clusters found using traditional surveillance.

RESULTS

The 62 alerts generated corresponded to 17 distinct signals of a potential outbreak. The signals had a median of eight cases (range: 3-106), seven zip code areas (range: 1-88), and seven days (range: 3-14). Two signals resulted from true clusters of varicella; six were plausible but unconfirmed indications of disease clusters, six were considered spurious, and three were not investigated. The median investigation time per signal by health departments was 50 minutes (range: 0-8 hours). Traditional surveillance picked up 124 clusters of illness in the same period, with a median of six ill per cluster (range: 2-75). None was related to syndromic signals.

CONCLUSIONS

The system was able to detect two true clusters of illness, but none was of public health interest. Possibly due to limited population coverage, the system did not detect any of 124 known clusters, many of which were small. The number of false alarms was reasonable.

Reduced binding and phagocytosis of Pneumocystis carinii by alveolar macrophages from persons infected with HIV-1 correlates with mannose receptor downregulation

The macrophage mannose receptor, a pattern recognition molecule and component of innate immunity, mediates binding and phagocytosis of Pneumocystis carinii and likely represents an important clearance mechanism in the lungs of immunocompetent hosts. The purpose of this study was to examine the ability of alveolar macrophages from HIV-infected individuals to bind and phagocytose P. carinii, and to investigate the role of the macrophage mannose receptor in mediating this interaction. Compared with healthy individuals, alveolar macrophage phagocytosis of P. carinii from HIV+ persons was reduced up to 74% (P = 0.02), primarily reflecting a reduction in the number of organisms associated with each macrophage (P = 0.019). Furthermore, macrophages from HIV+ individuals demonstrated up to an 80% (P < 0.05) reduction in mannose receptor surface expression and endocytosis. Mannose receptor affinity was unaltered, and mRNA levels were modestly reduced (P < 0.05). Cells from HIV+ individuals with CD4(+) counts < 200 cells/mm3 (representing individuals at high clinical risk for P. carinii pneumonia) demonstrated the lowest levels of P. carinii phagocytosis and mannose receptor endocytosis. In vitro HIV infection of alveolar macrophages from healthy individuals reduced mannose receptor endocytosis to 53.2% (P < 0.05) and P. carinii binding and phagocytosis to 67.4% (P < 0.05) of control. Our studies suggest that HIV infection may alter innate immunity in the lungs, and that impaired alveolar macrophage mannose receptor-mediated binding and phagocytosis of P. carinii may contribute to the susceptibility of HIV-infected individuals to this opportunistic pulmonary pathogen.

Th1 and Th2 cytokines cooperate to stimulate mannose-receptor-mediated phagocytosis

The mannose receptor is a macrophage surface receptor that mediates both endocytosis and phagocytosis. Previous work has demonstrated that the prototypical Th2 cytokine, interleukin-4 (IL-4), increases both cell-surface receptor expression and mannose receptor-mediated endocytosis, whereas the prototypical Th1 cytokine, interferon-gamma (IFN-gamma), decreases both surface expression and endocytosis. In many aspects of the immune response, Th1 and Th2 cytokines oppose each others' actions. We demonstrate that IL-4 and IFN-gamma alone and together enhance mannose receptor-mediated phagocytosis, despite opposing effects on cell-surface mannose receptor expression and endocytosis. Thus these usually antagonistic cytokines cooperate in increasing mannose receptor phagocytic function. The cooperative effect of these cytokines is not observed for Fc receptor-mediated phagocytosis. The Th2 cytokine IL-13 exerts similar effects to IL-4. Our results suggest that Th1 and Th2 cytokines may act in concert at sites of inflammation to enhance mannose receptor-mediated phagocytosis of microorganisms.

Targeted disruption of guanosine diphosphate-dissociation inhibitor for Rho-related proteins, GDID4: normal hematopoietic differentiation but subtle defect in superoxide production by macrophages derived from in vitro embryonal stem cell differentiation

The Rho subfamily of small guanosine triphosphate (GTP)-binding proteins, through their role in cytoskeletal organization, is involved in diverse cellular functions, including cell motility and morphologic changes during differentiation. Rac also has a special role in the production of superoxide, a key component in phagocytic antimicrobial function. Guanosine diphosphate (GDP)-dissociation inhibitors (GDIs) belong to one of three classes of proteins that regulate the critical cycling of GTP-binding proteins between the inactive and active states. Two homologous GDIs for the Rho subfamily have been identified. GDID4 is preferentially expressed in hematopoietic cells, while RhoGDI is ubiquitously expressed. Whether different physiologic functions are subserved by the two GDIs is unknown. We have derived embryonal stem (ES) cells with targeted disruption of both alleles of the GDID4 gene and examined hematopoiesis and phagocytic functions of macrophages derived from in vitro ES-cell differentiation. GDID4-/- ES cells develop like wild-type cells into colonies that contain heterogeneous populations of progenitor cells and differentiated erythromyeloid cells. GDID4-/- cells express no GDID4 protein, but have normal levels of RhoGDI. GDID4-/- macrophages phagocytose yeasts and antibody-opsonized erythrocytes as effectively as wild-type macrophages. However, a slight but consistent reduction in their capacity to generate superoxide was observed, which suggests new insight into the cellular role of GDID4. The minimal phenotypic effect of a loss of function of GDID4 also indicates a significant redundancy of function between GDID4 and RhoGDI. Their functional repertoire may be better revealed by a disruption of both genes. The use of hematopoietic cells derived in vitro from genotypically altered ES cells avoids the difficulties inherent in generating knockout animals and is a useful complementary approach for evaluating the gene function.

Role of macrophage oxidative burst in the action of anthrax lethal toxin

BACKGROUND

Major symptoms and death from systemic Bacillus anthracis infections are mediated by the action of the pathogen's lethal toxin on host macrophages. High levels of the toxin are cytolytic to macrophages, whereas low levels stimulate these cells to produce cytokines (interleukin-1 beta and tumor necrosis factor-alpha), which induce systemic shock and death.

MATERIALS AND METHODS

Experiments were performed to assess the possibility that the oxidative burst may be involved in one or both of lethal toxin's effects on macrophages. Toximediated cell lysis, superoxide anion and cytokine production were measured. Effects of antioxidants and macrophage mutations were examined.

RESULTS

RAW264.7 murine macrophages treated with high levels of toxin released large amounts of superoxide anion, beginning at about 1 hr, which correlates with the onset of cytolysis. Cytolysis could be blocked with various exogenous antioxidants or with N-acetyl-L-cysteine and methionine, which promote production of the endogenous antioxidant, glutathione. Mutant murine macrophage lines deficient in production of reactive oxygen intermediates (ROIs) were relatively insensitive to the lytic effects of the toxin, whereas a line with increased oxidative burst potential showed elevated sensitivity. Also, cultured blood monocyte-derived macrophages from a patient with Chronic Granulomatous Disease, a disorder in which the phagocyte's oxidative burst is disabled, were totally resistant to toxin, in contrast to control monocytes.

CONCLUSIONS

These results imply that the cytolytic effect of the toxin is mediated by ROIs. Additionally, cytokine production and consequent pathologies showed partial dependence on macrophage ROIs. Antioxidants moderately inhibited toxin-induced cytokine production in vitro, and BALB/c mice pretreated with N-acetyl-L-cysteine or mepacrine showed partial protection against lethal toxin. Thus ROIs are involved in both the cytolytic action of anthrax lethal toxin and the overall pathologic process in vivo.

Cytokines in the treatment of primary immunodeficiency

Cytokines have great potential in the treatment of primary immunodeficiencies, which is just beginning to be realized. We discuss some general considerations in the use of cytokines in this setting, and review the clinical use of a number of cytokines. The best proven example to date is the use of interferon-gamma in chronic granulomatous disease, which significantly reduces infectious complications of this disease. We also discuss the potential use of interferon-gamma in the hyperimmunoglobulin E syndrome and in newborns. Granulocyte-colony stimulating factor usage in congenital neutropenias is reviewed. The use of IL-2, thymic hormones, and interferon-alpha are briefly discussed. Strategies for the design of clinical trials of cytokines in these uncommon illnesses are proposed.

Neurocysticercosis in a child with no history of travel outside the continental United States

We present a case of neurocysticercosis in a 16-month-old girl who had no history of travel outside the continental United States. Immunoblot assays of serum and CSF were both reactive. The patient's father was found to be shedding Taenia ova in his stools, a finding that suggested direct fecal-oral transmission between himself and the patient. Given the possibility of this mode of transmission, the diagnosis of CNS cysticercosis should be considered for patients with compatible clinical presentations even if they do not have obvious risk factors such as travel to an area endemic for the parasite.

Phagocytic chimeric receptors require both transmembrane and cytoplasmic domains from the mannose receptor

Phagocytosis has traditionally been viewed as a specialized function of myeloid and monocytic cells. The mannose receptor (MR) is an opsonin-independent phagocytic receptor expressed on tissue macrophages. When human MR cDNA is transfected into Cos cells, these usually non-phagocytic cells express cell surface MR and bind and ingest MR ligands such as zymosan, yeast, and Pneumocystis carinii. Expression of cDNA for Fc gamma RI (CD64), the high-affinity Fc receptor, in Cos cells confers binding but barely detectable phagocytosis of antibody-opsonized erythrocytes (EA). We report here that chimeric receptors containing the ligand-binding ectodomain of the Fc receptor and the transmembrane and cytoplasmic domains of the MR ingest bound EA very efficiently, whereas chimeras with the Fc receptor ecto- and transmembrane domains and the MR tail, or the Fc receptor ecto- and cytoplasmic domains and the MR transmembrane region, are significantly less phagocytic. All of the chimeric receptors bind ligand with equal avidity, but gain of functional phagocytosis is only conferred by the MR transmembrane and cytoplasmic domains. Endocytosis of monomeric immunoglobulin G by chimeric receptors demonstrates a similar pattern, with optimal uptake by the chimera containing both tail and transmembrane regions from the MR. The chimeric receptors with only the transmembrane or the cytoplasmic domain contributed by the MR were less efficient. Site-directed mutagenesis of the single tyrosine residue in the cytoplasmic tail (which is present in a motif homologous to an endocytosis consensus motif in the LDL receptor cytoplasmic tail [Chen, W.-J., J. L. Goldstein, and M. S. Brown. 1990. J. Biol. Chem. 265:3116]) reduces the efficiency of phagocytosis and endocytosis to a similar extent.

Simultaneous addition of EGF prolongs the increase in cytosolic free calcium seen in response to bradykinin in NRK-49F cells

The calcium-sensitive fluorescent indicator fura-2 and a microscope equipped for rapidly changing excitation wavelengths were used to look at the effects of growth factors on cytosolic free calcium ([Ca2+]i) in NRK-49F cells. In these cells bradykinin induced a rapid increase in [Ca2+]i, which generally decayed to near basal [Ca2+]i within 3 minutes. The initial rise in [Ca2+]i in response to bradykinin was relatively independent of extracellular calcium; however, the decay to basal [Ca2+]i was more rapid in the absence of extracellular calcium. Measurements made on individual cells showed a heterogeneity in the response to bradykinin. Epidermal growth factor (EGF) had no effect on [Ca2+]i in NRK-49F cells when added alone in the presence of extracellular calcium. Simultaneous addition of bradykinin and EGF produced a more prolonged increase in [Ca2+]i than bradykinin alone. The prolongation was dependent on the presence of extracellular calcium and did not occur in its absence. Transient increases in [Ca2+]i occurring after the initial peak were occasionally seen in these cells. Our results indicate that there is rapid interaction between the signaling mechanisms for bradykinin and EGF. When this occurs, one effect is the transport of calcium into the cell from the extracellular environment, causing a more prolonged rise in [Ca2+]i. This effect occurs within 1 minute after combined addition of bradykinin and EGF.

Cytosolic free calcium increases before and oscillates during frustrated phagocytosis in macrophages

When macrophages and neutrophils are allowed to settle onto an appropriate surface, they attach and spread in a frustrated attempt to phagocytose the substrate. Spreading is associated with extensive rearrangements of the actin cytoskeleton which resemble those occurring during phagocytosis. We have previously shown that spreading in human neutrophils is preceded by an increase in cytosolic-free calcium concentration [( Ca2+]i) (Kruskal, B. A., S. Shak, and F. R. Maxfield. 1986. Proc. Natl. Acad. Sci. USA. 83:2919-2923). To assess the generality of this signal, we measured [Ca2+]i in single thioglycollate-elicited mouse peritoneal macrophages as they spread on an immune complex-coated surface, using fura-2 microspectrofluorometry. A [Ca2+]i increase always precedes spreading. This increase can involve several (up to 8) [Ca2+]i spikes, with an average peak value of 387 +/- 227 nM (mean +/- SD, n = 92 peaks in 24 cells), before spreading is detected. Neither spreading nor the magnitude of these spikes is significantly altered by removal of extracellular calcium. Many of the spreading macrophages exhibit periodic [Ca2+]i increases before and during spreading. The proportion which does so varies among experiments from 0 to 90%, but it is frequently greater than 40%. The largest number of cells (approximately 25%) exhibited only a single peak. In 13 cells that showed more than 10 peaks, the median period was 29 s (range 19-69 s). The average peak [Ca2+]i was 385 +/- 266 nM (mean +/- SD, n = 208 peaks in 14 cells). The calcium producing these increases is derived from intracellular pools. The oscillations occur with spreading on either opsonized or nonopsonized surfaces. The function of these oscillations is not clear, but the large number of cells which exhibit them suggest that they may be important to macrophage function.

Spreading of human neutrophils is immediately preceded by a large increase in cytoplasmic free calcium

When human polymorphonuclear leukocytes (PMN) are placed on various surfaces, they attach and spread rapidly, increasing their diameter severalfold. The spreading is associated with extensive changes in the cytoskeleton. Since many cytoskeletal events are regulated by Ca2+, we measured the cytosolic free calcium concentration ([Ca2+]i) in individual human PMN as they spread. [Ca2+]i was measured in single cells by microspectrofluorometry using the fluorescent Ca2+-sensitive dye fura-2. Immediately before spreading, PMN exhibit a rapid increase in [Ca2+]i, from 69 +/- 51 nM to 547 +/- 190 nM (mean +/- SD, n = 12). [Ca2+]i returns to near resting levels during the next minute, as the cells spread. Neither the spreading nor the [Ca2+]i spike is blocked by removal of extracellular calcium, by verapamil, by calmodulin antagonists, or by mitochondrial or microtubule poisons. Spreading, but not the [Ca2+]i increase, is blocked by the microfilament inhibitor cytochalasin B. Both spreading and the [Ca2+]i spike are blocked by ATP depletion and reversibly blocked by placing the cells in medium containing hypertonic sucrose or sodium chloride. These data strongly suggest that an increase in [Ca2+]i, derived from nonmitochondrial intracellular pools, plays an important role in the microfilament-mediated process of PMN spreading.

Thyrotropin-releasing hormone-induced changes in intracellular [Ca2+] measured by microspectrofluorometry on individual quin2-loaded cells

We have developed an accurate and practical method for measuring intracellular Ca2+ concentration [( Ca2+]i) in single cells in monolayer culture using the fluorescent Ca2+-binding dye quin2. Quin2 was loaded into cells as a membrane-permeant ester which is hydrolyzed in the cytoplasm to the impermeant free acid, which is the indicator form (Tsien, R.Y., T. Pozzan, and T.J. Rink, 1982, J. Cell Biol., 94:325-334). The method involves the measurement of fluorescence at 340-nm excitation (I340), where dye fluorescence is dependent on Ca2+, and at 360-nm excitation (I360), where dye fluorescence is independent of Ca2+. The ratio of these two values (I340/I360) is thus related to the concentration of Ca2+ but independent of dye concentration and can be used as a measure of [Ca2+]. To test the ratio method in the microscope, we measured [Ca2+]i in GH3 cells in monolayer culture. We found a resting [Ca2+]i of 44 +/- 28 nM (mean +/- SD, n = 34), as compared with a suspension value (Gershengorn, M., and C. Thaw, 1983, Endocrinology, 113:1522-1524) of 118 +/- 18 nM. We also measured [Ca2+]i during stimulation of the cells with thyrotropin-releasing hormone (TRH) and found a 2.4-fold increase above resting levels within 20 s, a trough at 73% of resting at 90-100 s, and a peak slightly above resting at 3 min. Depolarization of the plasma membrane with KCl produced a sustained increase in [Ca2+]i. All of these data are in good agreement with the results of Gershengorn and Thaw on suspension cultures. When measuring both resting [Ca2+]i and the effects of TRH and KCl on small groups of cells, we found some variation among experiments. Using an image intensifier-video camera, we videotaped cells during TRH stimulation. Digital image analysis of these pictures demonstrated that there was a large variation in responsiveness from cell to cell. The microscope ratio method offers the possibility of resolving regions of differing [Ca2+] within the cytoplasm.