Human peripheral blood B-cell compartments: a crossroad in B-cell traffic

A relatively high number of different subsets of B-cells are generated through the differentiation of early B-cell precursors into mature B-lymphocytes in the bone marrow (BM) and antigen-triggered maturation of germinal center B-cells into memory B-lymphocytes and plasmablasts in lymphoid tissues. These B-cell subpopulations, which are produced in the BM and lymphoid tissues, recirculate through peripheral blood (PB), into different tissues including mucosa and the BM, where long-living plasma cells produce antibodies. These circulating PB B-cells can be classified according to their maturation stage into i) immature/transitional, ii) naïve, and iii) memory B-lymphocytes, and iv) plasmablasts/plasma cells. Additionally, unique subsets of memory B-lymphocytes and plasmablasts/plasma cells can be identified based on their differential expression of unique Ig-heavy chain isotypes (e.g.: IgM, IgD, IgG, IgA). In the present paper, we review recent data reported in the literature about the distribution, immunophenotypic and functional characteristics of these cell subpopulations, as well as their distribution in PB according to age and seasonal changes. Additional information is also provided in this regard based on the study of a population-based cohort of 600 healthy adults aged from 20 to 80 years, recruited in the Salamanca area in western Spain. Detailed knowledge of the distribution and traffic of B-cell subsets through PB mirrors the immune status of an individual subject and it may also contribute to a better understanding of B-cell disorders related to B-cell biology and homeostasis, such as monoclonal B-cell lymphocytosis (MBL).

Fluorescence intensity calibration for immunophenotyping by flow cytometry

Fluorescence intensity (FI) is the basis for classifying phenotypes by fluorescence-label flow cytometry. FI is customarily recorded as an arbitrary relative value, but with proper calibration it can be expressed in stoichiometric units called molecules of equivalent soluble fluorochrome (MESF) that reflect the concentrations of the fluorescent conjugates and the receptors they stain. Forthcoming availability of authoritative standards and consensus methods will alleviate many of the difficulties encountered in making valid MESF measurements. FI calibration establishes the true values for the critical parameters of the fluorescence measurement, a useful feature for quality control. It further allows the establishment of a comparable window of analysis across different times and laboratories, and it permits numeric assessment of antibody-binding capacity (ABC) values in selected cell populations. The relation between ABC values and receptor expression is complicated by several factors, but careful assessment of the binding chemistry can establish the actual number of receptors on cells stained by fluorescent conjugates.

Serum immunoglobulins and lymphocyte subset distributions in children and adults living in communities assessed for lead and cadmium exposure

This study assessed the impact of environmental cadmium and lead exposure on the immune system of more than 2000 children and adults. Serum immunoglobulins [immunoglobulins (Ig) A, G, and M] and peripheral blood lymphocyte phenotypes (T cells, B cells, NK cells, and CD4/CD8 subsets) were measured in a total of 2041 children and adults who lived either in sites with elevated soil levels of cadmium and lead (n = 1561) or in comparison communities (n = 480). The blood lead and urine cadmium levels of participants were somewhat higher than national averages. Mean blood lead levels were 7 microg/dl for participants aged 6-35 mo; 6 microg/dl for participants aged 36-71 mo, 4 microg/dl for participants aged 6-15 yr; and 4.3 microg/dl for participants aged 16-75 yr. Multivariate analysis indicated no marked differences in any of the immune marker distributions attributed to lead for adults or children over 3 yr of age. However, in children under age 3, increased blood lead levels, principally those over 15 microg/dl, were associated with increases in IgA, IgG, IgM, and circulating B lymphocytes. Among adults, urine cadmium levels over 1.5 microg/g were associated with higher levels of IgA and circulating B lymphocytes. No evidence of immunosuppression was noted. The findings of potential immunologic effects at lead levels > 15 microg/dl in young children and at urine cadmium levels > 1.5 microg/g in adults are interesting, but too few participants had these high levels to delineate a threshold. Therefore, we find these results intriguing, but requiring confirmation in populations with higher exposure levels.

Increased lymphocyte replicative index following 2,4-dichlorophenoxyacetic acid herbicide exposure

OBJECTIVE

Evaluate peripheral blood lymphocyte proliferation (replicative index:RI) and micronuclei frequency (MF) among 2,4-D herbicide applicators.

METHODS

Twelve applicators spraying only 2,4-D provided a blood and urine specimen upon enrollment, several urine samples during the spraying season, and a blood specimen at the study's end. Nine controls provided blood and urine specimens upon enrollment and at the study's end. Gas chromatography/tandem mass spectroscopy determined urinary 2,4-D levels and standard in-vitro assays determined RI and MF scores. Applicator RI and MF were compared before and after spraying and with controls.

RESULTS

Applicators contributed 45 urine specimens with concentrations ranging from 1.0 to 1700 (microg 2,4-D/g creatinine/L urine) that logarithmically (In) increased as spraying time increased. Applicator RI increased after spraying (p = 0.016), independent of tobacco and alcohol use, and demonstrated a weak dose-response with increasing urinary 2,4-D levels (p = 0.15). Among 2,4-D applicators, pre-exposure complete blood counts and lymphocyte immunophenotypes were not significantly different from post-exposure measurements.

CONCLUSION

Urinary 2,4-D concentration, an exposure biomarker, may be associated with lymphocyte replicative index, a cell proliferation biomarker.

Current activities at the Centers for Disease Control and Prevention's National Diabetes Laboratory

In 1997, the Centers for Disease Control and Prevention established the National Diabetes Laboratory in order to help prevent and treat type 1 diabetes. This state-of-the-art laboratory collaborates with research scientists and key national and international organizations throughout the world to identify and study risk factors for type 1 diabetes by developing measurements for glycosylated proteins, developing and evaluating technology for measuring genetic risk factors for the disease, and working to standardize autoantibody measurements. Developing improved technologies for diagnosing and managing diabetes and developing reference materials for properly calibrating and standardizing blood glucose meters are also critical aspects of the laboratory's work. In addition, the laboratory provides quality storage for valuable collections of biologics and other materials and facilitates sharing of specimens, associated epidemiologic data, and test results. Working with our partners in diabetes research, we are improving the diagnosis, treatment, and prevention of type 1 diabetes.

Titration of a CD45-FITC conjugate to determine the linearity and dynamic range of fluorescence intensity measurements on lymphocytes

To produce biologic calibrators for relative fluorescence intensity (RFI) measurements, we stained leukocytes with serial dilutions of CD45-FITC conjugate and processed them using our regular whole blood lysis procedure. Cells were stained with conjugate concentrations ranging from twice recommended to a million-fold lower. At the highest concentrations of conjugate, the RFI reached a plateau near the top of the third decade, indicating saturation of CD45 binding sites. As the concentration decreased, the RFI declined in a highly linear relationship between the dilution factor and the histogram channel number. For channel numbers corresponding to the lowest percentiles of the RFI distribution, linearity persisted down to the first half decade. The slope of this relationship revealed a true dynamic range of 4.5 decades, which was comparable to the value obtained with microbead standards calibrated in molecules of equivalent soluble fluorochrome (MESF). Our results suggest that the lower limit of linearity for fluorescence intensity from fluorescein isothiocyanate (FITC)-stained lymphocytes is below 500 MESF and that cellular autofluorescence is the major limiting factor in detecting and quantifying FITC-specific staining. This procedure provides an adroit way of characterizing the linearity and dynamic range of measurements for quantitative fluorescence cytometry using exactly the same matrix, stains, and preparation methods as those used for cellular analytes.

Terminology and nomenclature for standardization in quantitative fluorescence cytometry

Terminology in any field is a complex mix of established conventions, accepted usages, disputed terms, and occasional misnomers. The terminology that has evolved for quantitative fluorescence cytometry (QFCM) is especially multifarious, in part because QFCM encompasses a range from subjective visual assessments to objective photon counts. Thus, while descriptive terms such as "dim" and "bright" are still quite useful, quantitative terms such as "binding capacity" should be used with collective understanding of their exact meanings. This article reviews current usage and proposes definitions that, with refinement from suppliers and users of QFCM technology, can provide the required clarity.

Application of neural networks to flow cytometry data analysis and real-time cell classification

Conventional analysis of flow cytometric data requires that population identification be performed graphically after a sample has been run using two-parameter scatter plots. As more parameters are measured, the number of possible two-parameter plots increases geometrically, making data analysis increasingly cumbersome. Artificial Neural Systems (ANS), also known as neural networks, are a powerful and convenient method for overcoming this data bottleneck. ANS "learn" to make classifications using all of the measured parameters simultaneously. Mathematical models and programming expertise are not required. ANS are inherently parallel so that high processing speed can be achieved. Because ANS are nonlinear, curved class boundaries and other nonlinearities can emerge naturally. Here, we present biomedical and oceanographic data to demonstrate the useful properties of neural networks for processing and analyzing flow cytometry data. We show that ANS are equally useful for human leukocytes and marine plankton data. They can easily accommodate nonlinear variations in data, detect subtle changes in measurements, interpolate and classify cells they were not trained on, and analyze multiparameter cell data in real time. Real-time classification of a mixture of six cyanobacteria strains was achieved with an average accuracy of 98%.

Computing the central location of immunofluorescence distributions: logarithmic data transformations are not always appropriate

The idea of the "average" intensity of immunofluorescence data is often poorly defined, with such terms as average, mean, and peak used interchangeably. In addition, the common use of logarithmic amplifiers with immunofluorescence data further complicates the problem. Log amplifiers permit the display of a wider range of fluorescence intensities. At the same time, they effect a log transformation of the data. This transformation decreases the variance resulting in narrower fluorescence distributions, which are assumed to approximate normal distributions. When the log transform is used, the distribution mean is the geometric mean of the untransformed data, which is computed simply as the mean of the channel values. This mean value serves as a simple indicator of the population center. Despite the prevalence of log transformations in flow cytometry, this transformation may not yield normally distributed immunofluorescence data, whereas the square root or other fractional power transformations can yield normal distributions.

Comparison of lymphocyte immunophenotypes obtained simultaneously from two different data acquisition and analysis systems on the same flow cytometer

Immunophenotyping of different lymphocyte populations was carried out in parallel on 113 consecutively received specimens of human peripheral blood using 2 different data acquisition and analysis systems (EPICS C and 4Cyte-Acmecyte) on the same flow cytometer (EPICS C). The phenotypes analyzed were CD3+, CD4+, CD8+ CD56+ CD16+ CD3-, TCR-gamma delta+ CD8-, and TCR-gamma delta+ CD8+. Both HIV- and HIV+ specimens were used for this study, including some with CD4 levels as low as 2% of all lymphocytes. Despite differences in gating procedures and shapes of bitmap (rectilinear vs. "amorphous"), the 2 methods agreed to within 2% positive cells in 97% of the cases. Although some statistically significant biases in the methods were observed, these were small and not biologically important. We conclude that both methods of data acquisition and analysis, as employed by experienced operators on the EPICS C flow cytometer, gave essentially equivalent results for lymphocyte sub-populations in peripheral blood preparations.

Use of laboratory tests for immune biomarkers in environmental health studies concerned with exposure to indoor air pollutants

The immune system is likely to be involved in some of the health effects caused by certain indoor air exposures, and immune biomarkers can help determine which exposures and health effects have important immune components. However, the lack of standardized laboratory tests for most human immune markers and the many confounding variables that can influence them makes interpretation of results for exposure and disease end points uncertain. This paper presents an overview of the immune system and the considerations involved in using tests for immune markers in clinical epidemiology studies, particularly those concerned with indoor air exposures. Careful study design, well-characterized laboratory methods, and rigorous documentation of exposure status are required to determine the predictive value of such tests. Clinical tests currently available for some immune markers could help identify and characterize both irritative and hypersensitivity reactions to indoor air pollutants. Newer tests developed in research settings might provide more incisive indicators of immune status that could help identify exposure, susceptibility, or preclinical disease states, but their methodologies must be refined and tested in multicenter studies before they can be used reliably in public health applications.

Interlaboratory study of cellular fluorescence intensity measurements with fluorescein-labeled microbead standards

To determine the precision of cellular fluorescence intensity (FI) measurements derived from labeled microbead standards, FI results were compared from 43 different flow cytometers in 34 laboratories. All laboratories analyzed prepared aliquots of fluoresceinated calf thymocyte nuclei (Fluorotrol), human lymphocytes stained with fluoresceinated anti-CD4 antibody, and fluoresceinated microbeads used as both internal and external standards. Measurements were conducted by most laboratories on the third and fourth days after sample preparation. Results for percent of events within the gates and the histograms returned by participants indicated that the samples had remained stable and that gated populations had been properly identified. All standard curves showed strong linearity, and the pooled results from all standards produced a best-fit curve that was in close agreement with the assigned values. Nonetheless, results for cellular FI were highly variable, with CVs of 20-34%. Agreement within lab/instrument was much better, with CVs ranging from 3.0 to 9.9%. The overall variability was not obviously attributable to differences in the types of cytometer, nor could it be explained by attributes of the standard curves or any other single variable examined. However, the application of a corrective factor based on FI results for Fluorotrol allowed a two-fold improvement in the precision of FI measurements on CD4-stained lymphocytes, with an overall CV of 11%. Uncharacterized differences in the operating conditions of flow cytometers can influence cellular FI measurements, but consistent results can be obtained if a stained cellular calibrator is analyzed in addition to the proper microbead standards.

Model system evaluating fluorescein-labeled microbeads as internal standards to calibrate fluorescence intensity on flow cytometers

Fluorescence intensity calibration was evaluated in a model system for flow cytometers using commercially available fluorescein-labeled microbeads as internal standards and stabilized fluoresceinated thymus cell nuclei (Fluorotrol) as surrogates for stained mononuclear cells. Spectrophotometrically determined calibration values for the microbeads were used to generate a standard curve that converted green fluorescence histogram channels into molecular equivalents of soluble fluorescein (MESF). In 19 analyses repeated during a single run, the coefficients of variation (CVs) for the derived MESF values on both dimly and brightly stained Fluorotrol populations were less than 2%. In 26 separate determinations over 14 weeks, the CVs of the derived MESF values were less than 3%. The MESF values of the dim and bright Fluorotrol populations derived from the microbead standard curves were both about 50% lower than those determined by direct spectrophotometric analysis of Fluorotrol. The analytical imprecision of fluorescence intensity measurements in this idealized model system has a CV less than 3%, and the analytical inaccuracy shows that calibration in MESF units remains uncertain over about a two-fold range.

Quantitative differences among various proteins as blocking agents for ELISA microtiter plates

We tested instantized dry milk, casein, gelatins from pig and fish skin, serum albumin and several other proteins for their abilities to block non-specific binding (NSB) of a peroxidase-conjugated immunoglobulin to polystyrene microtiter plate wells. Each blocking protein was tested across a million-fold concentration range, both in simultaneous incubation with the peroxidase conjugate and as a pretreatment agent where excess protein was washed away before incubation with the conjugate. Overall, instantized milk and casein were the most effective proteins tested: they inhibited NSB by over 90% in both the simultaneous and pretreatment modes at far lower concentrations than most of eight other proteins. Enzymatically hydrolyzed porcine skin gelatin was the least effective protein tested: it did not reduce NSB by more than 90% even at its highest concentrations; its blocking ability fell rapidly upon dilution; and it was almost useless as a pretreatment agent. Fish skin gelatin showed much better blocking activity than hydrolyzed porcine gelatin, and it still had the practical advantage of remaining fluid even under refrigeration. Our results suggest that some proteins (such as casein) block NSB to plastic primarily through protein-plastic interactions, while others (such as porcine skin gelatin) block primarily through protein-protein interactions. Although the optimal blocking agent for any particular ELISA system must be determined by empirical testing, these results should be helpful in selecting the best possible candidate proteins for further evaluation.

Inflammatory mediators and modulators released in organ culture from rabbit skin lesions produced in vivo by sulfur mustard. III. Electrophoretic protein fractions, trypsin-inhibitory capacity, alpha 1-proteinase inhibitor, and alpha 1- and alpha 2-macroglobulin proteinase inhibitors of culture fluids and serum

This is the third report in a series on the inflammatory mediators and modulators released in organ culture from skin lesions of various ages, which were produced in vivo in rabbits by the military vesicant, sulfur mustard (SM). It describes the electrophoretic protein fractions and trypsin-inhibitory capacities of the various culture fluids and the amounts of alpha 1-proteinase inhibitor and alpha-macroglobulin proteinase inhibitors in these fluids. With one-dimensional electrophoresis, the albumin and beta-globulin fractions of protein in culture fluids varied little with the development and healing of the SM lesions. These fractions proportionally resembled the corresponding fractions found in serum. The alpha 1-globulin fraction was proportionally smaller than the corresponding fractions of serum as the lesions healed. The alpha 2-globulin fraction was proportionally smaller than the corresponding fractions of serum at all stages of lesion development and healing. The gamma-globulin fraction was proportionally larger as the lesions healed. With two-dimensional electrophoresis, about 68%, 46%, and 35% of the protein spots in culture fluids from representative 1-day and 6-day SM lesions and normal skin, respectively, matched those from serum. In each case, the large, diffuse, serum albumin spot represented about two-thirds of the protein present. Thus, gravimetrically, in normal skin and in both developing and healing lesions, the extracellular proteins were 80-90% of serum origin. The trypsin-inhibitory capacity (TIC) per milligram protein in the culture fluids of healing lesions was markedly less than the TIC per milligram protein in the fluids of peak lesions. This decrease correlates well with the decrease found in the alpha 1-globulin fraction, which contains alpha 1-antiproteinase (alpha 1-PI) (and alpha 1-macroglobulin [alpha 1M] in rabbits). The alpha 1PI and the alpha 1M-alpha 2M proteinase inhibitors were identified in the culture fluids by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blots, specific antibodies, and the immuno-peroxidase technique. The levels of both free and proteinase-complexed alpha 1PI and alpha M inhibitors in the culture fluids decreased as the lesions healed. In both developing and healing lesions, at least half of the alpha 1PI and alpha M inhibitors seemed to be complexed with proteinases. Thus, serum seems to be a major source of unbounded extracellular protein within acute inflammatory lesions, and serum proteinase inhibitors seem to be the host's major defense against local damage by proteinases from serum, infiltrating leukocytes, and activated fibroblasts.

Measurement of myelin basic protein by radioimmunoassay in closed head trauma, multiple sclerosis and other neurological diseases

A double antibody sequential radioimmunoassay for human myelin basic protein (MBP) has been developed. The assay utilizes a rabbit antibody to human MBP and purified rabbit MBP as the radiolabelled antigen. This assay was used to analyze cerebrospinal fluid (CSF) from 22 patients with severe head injury, 61 other cases of various neurological disorders, and 106 normal controls. The results showed that closed head trauma caused moderate to severe elevations in CSF MBP, and elevated CSF MBP was detectable in several diseases which involve CNS myelin.

Inflammatory mediators and modulators released in organ culture from rabbit skin lesions produced in vivo by sulfur mustard. I. Quantitative histopathology; PMN, basophil, and mononuclear cell survival; and unbound (serum) protein content

When applied topically to the skin of rabbits in vivo, sulfur mustard (SM), the vesicant used in World War I, produced a slowly developing inflammatory response, which peaked in size at 1 and 2 days, ulcerated within 3 days, and reepithelialized by 10 days. Histologically, basophils and polymorphonuclear leukocytes (PMNs) were common in both early and late lesions, and the crust over the ulcers was composed of dead epidermal cells, fibrin, and large numbers of PMNs. Healing occurred under the crust by migration of epidermal cells from the margins of the lesions and from the hair follicles. In organ culture, the lesion explants survived well, and reepithelialization even took place. Their excellent survival enabled us to compare the life spans of the infiltrating leukocytes within an inflammatory site. PMNs within the explants began disappearing during the first day of culture, and almost all had disappeared by 3 days. In contrast, over half of the basophils and the mononuclear cells within the explants were still present after 3 days of culture. The 1-, 2-, 3-, 6-, and 10-day (1.0-sq cm) SM lesion biopsies showed a 30-45% increase in weight (when compared with normal skin), presumably due to the extravasation of serum proteins and the fluids retained by them. When the biopsies were organ-cultured for 3 days, the 1-, 2-, and 3-day lesions lost weight, and the 6- and 10-day lesions (and normal skin) gained weight. These weight differences were not due to the amount of unbound protein extractable into the culture fluids, because both the early lesions and the late lesions contained about the same amount of unbound protein. The most likely explanation for these weight differences is that the newly formed ground substances of late lesions absorbed culture fluid, because the ground substance had changed from the sol state of acute inflammation (in which it was extractable) back to its normal gel state (in which it was not extractable). The unbound protein extractable into the culture fluids was mostly of serum origin. This protein averaged 1.9 mg for 1.0 sq cm normal skin explants (with a mean weight of 215 mg), and 6.4 mg for 1-day SM lesions (with a mean weight of 313 mg). Because rabbit serum contains about 60 mg protein/ml, these figures indicate that normal skin contained about 15% (unbound) serum by weight.(ABSTRACT TRUNCATED AT 400 WORDS)

Pathogenesis of skin lesions caused by sulfur mustard

Sulfur mustard (SM) (di-2-chlorethyl sulfide), used for chemical warfare in World War I, is a highly reactive radiomimetic alkylating agent. When applied to the skin of rabbits and guinea pigs, it produced vascular leakage, leukocyte infiltration, and slow death of basal epidermal cells. Thirty to sixty minutes after exposure to SM, injury to the superficial microvasculature (beneath the SM application site) was detected by measuring vascular leakage with Evans blue dye and also with horseradish peroxidase. At this same time, injury to the superficial fibroblasts was observed ultrastructurally; and an unexpectedly high percentage of basophils was found among the early infiltrating granulocytes. At 2 to 4 hr, the vascular leakage ceased, and had resumed by 8 hr in a more diffuse form. At this time, the basal epidermal cells showed pyknotic nuclei, an increase in their lysosomal enzymes (observed histochemically), and autophagic vacuoles (observed ultrastructurally). Leukocyte infiltration was marked, consisting mostly of heterophils (PMN) with a reduced percentage of basophils. During the next 24 to 72 hr, the entire inflammatory reaction reached its peak; and a superficial, crust-covered ulcer developed. Then, over the next 10 days, the lesion gradually subsided with concomitant repair and healing. Glucocorticosteroids decreased the early edematous phase, but did not affect the rate of healing. These findings suggest that the skin response to sulfur mustard has an immediate and a delayed phase. The immediate phase, i.e., within the first hour, was characterized by injury to the superficial fibroblasts and to the endothelium of superficial capillaries and venules, possibly because of direct damage to their cell membranes. At this time, a restricted vascular leakage and a selective granulocyte infiltration containing many basophils occurred. The delayed phase, which became evident after 8 hr, was characterized by the death of basal epidermal cells, probably because of DNA damage. This phase was accompanied by generalized vascular leakage, by massive heterophil immigration, and eventually by ulceration.

Improved techniques using Giemsa stained glycol methacrylate tissue sections to quantitate basophils and other leukocytes in inflammatory skin lesions

Improved techniques were developed for processing inflammatory skin lesions in glycol methacrylate (JB-4, Polysciences, Inc.) and for quantitating their leukocyte infiltrates by light microscopy: (1) fixation of entire pelts from rabbits, guinea pigs, rats and mice bearing multiple lesions eliminated artifacts due to biopsy and produced uniformly oriented skin sections; (2) adding dimethylsulfoxide and hydrogen peroxide to the Karnovsky-type fixative increased the rate and effectiveness of fixation; (3) the presence of glycerol in the infiltrating methacrylate and the polymerized plastic block improved the sectionability of skin and other tissues; (4) coating slides with JB-4 Solution A prevented detachment of specimens; (5) Giemsa staining at a carefully selected pH provided optimal differentiation of leukocytes from the several species examined, including man. These techniques, which allowed an accurate histologic assessment of inflammatory skin lesions, were especially valuable for quantitating basophils.