Phagocytosis measured as inhibition of uridine uptake by Candida albicans

Peripheral blood neutrophils of germ-free rats modified by in vivo granulocyte-colony-stimulating factor and exposure to natural environment

Peripheral blood neutrophils from germ-free (GF), specific-pathogen-free (SPF) and conventional (CV) rats were compared. Besides neutropenia and impaired superoxide anion generation as previously reported, it was found that GF rats had lower phagocytic function (70%) and generated less nitric oxide than the other rats. GF and SPF rats were injected with recombinant human granulocyte-colony-stimulating factor (rhG-CSF), or were transferred to natural environment. It was found that total number, phagocytosis, intracellular killing, ratio of phagocytosis versus killing (killing efficiency) and nitric oxide production induced by recombinant rat interferon-gamma (rrIFN-gamma) were normalized upon injection of rhG-CSF. These results indicate that rhG-CSF may stimulate neutrophil production and induce the expression of neutrophil receptors for phagocytosis and nitric oxide production in GF rats. Although lower than in CV rats, the level of superoxide produced was sufficient for normal neutrophil-killing efficiency in SPF and GF rats. In SPF rats, this could be amended by exposure to natural environment. However, neither rhG-CSF injection nor transfer to natural environment could increase the generation of superoxide anion in GF rats.

Quantitative measurement of lymphocyte mediated growth inhibition of Candida albicans

A rapid and reproducible assay has been developed to measure the capacity of lymphocytes to inhibit the growth of Candida albicans. Fungal growth inhibition was assessed optimally as the incorporation of [3H]uridine into preformed hyphae, following interaction of the hyphae with effector lymphocytes. The assay was sensitive to the detection of fungal growth inhibition by lymphocytes at low effector to target ratios and results correlated well with other methods for measurement of anti-C. albicans growth inhibition in vitro. Although the assay was developed for the measurement of lymphocyte mediated anti-fungal activity, other mammalian cell populations can be assayed for growth inhibition of C. albicans as well. The described assay utilizes the enzyme lyticase to reduce the surface binding of C. albicans. The use of this enzyme permits the efficient harvest of large numbers of experimental samples with a multiple automated sample harvester.

The development of a radiometric assay for monocyte phagocytosis and killing

Monocyte and macrophage phagocytosis and killing has an important role in host defence against infectious microorganisms. Established methods for investigating these activities in vitro are time-consuming, expensive and prone to subjective error. An in vitro assay has been developed which measures monocyte phagocytosis and killing of Candida albicans. In this system, monocyte function is assessed by a radiometric assay based on the incorporation of [3H]uridine into viable yeast cells. This technique allows the simultaneous but independent measurement of the average number of yeast cells ingested by monocytes and the percentage of the ingested organisms killed within a defined incubation period. These tests can be carried out on a single sample of peripheral blood, are relatively easy to perform, and provide objective results within 24 h of receipt of the specimen. This method gave consistent results when monocyte-enriched harvests were obtained by four different separation techniques. This assay could prove a valuable tool for the investigation of monocyte function in individuals with recurrent infections to determine the contribution this makes to their clinical condition. It may also be used to investigate in vitro the influence of cytokines and other chemical agents on monocyte function.

In vitro effect of diacetoxyscirpenol and deoxynivalenol on microbicidal activity of murine peritoneal macrophages

Diacetoxyscirpenol and deoxynivalenol, two trichothecene mycotoxins shown previously to exert immunosuppressive effects on the immune system were examined for their in vitro effects on some functions of murine peritoneal macrophages. The cells were pre-incubated for 4 hr with the mycotoxin concentrations of 0.1 ng/ml-1 micrograms/ml. At concentrations that did not affect the cell viability (Specific Lactate Dehydrogenase test), diacetoxyscirpenol and deoxynivalenol suppress microbicidal activity of phagocytic cells. The diacetoxyscirpenol concentrations, which reduce phagocytosis (2 ng/ml), microbicidal activity (1 ng/ml), superoxide anion production (1 ng/ml) and phagosome-lysosome fusion (0.1 ng/ml), indicate that the inhibition of killing mechanism arise from both oxidative and non-oxidative pathways. Phagocytosis, microbicidal activity and superoxide anion production are inhibited by deoxynivalenol at 1 ng/ml whereas phagosome-lysosome fusion is reduce above 100 ng/ml. These results suggest that microbicidal activity inhibition by deoxynivalenol did not depend on non-oxidative pathway (phagosome-lysosome fusion) impairment.

Flow cytometric assay for quantifying opsonophagocytosis and killing of Staphylococcus aureus by peripheral blood leukocytes

We describe a novel flow cytometric method for quantifying opsonophagocytosis and killing of Staphylococcus aureus in cell-rich plasma obtained after dextran sedimentation of erythrocytes. To analyze opsonophagocytosis, phagocytes were labeled with a phycoerythrin-conjugated monoclonal antibody and were incubated with viable staphylococci containing carboxyfluorescein as a vital fluorescent dye. Phagocytosing cells assumed a dual, orange-green fluorescence. The relative numbers of bacteria associating with phagocytes could be determined by quantifying the decrease of free green fluorescent particles. A parallel incubation of fluorescent bacteria with unlabeled cell-rich plasma was performed to assess phagocytic killing. Blood cells were lysed with 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate. This detergent spared viable bacteria, and residual green fluorescent particles were counted. The decrease in the number of these particles relative to the controls yielded the degree of killing. At bacteria-to-phagocyte ratios of 1:1 and 10:1, approximately 36 and 75% of the phagocytes participated in opsonophagocytosis, respectively. Over 90% of the staphylococci were phagocyte associated after 30 to 60 min. Killing rates were on the order of 66% +/- 12% and 80% +/- 7% after 1 and 2 h of incubation, respectively. These numbers, which were confirmed by colony countings, were significantly lower than those reported in the majority of past reports.

Growth inhibition of Candida albicans by interleukin-2-activated splenocytes

Murine splenocytes, Percoll-enriched low-density lymphocytes, and interleukin-2 (IL-2)-activated lymphocytes were assessed for the capacity to limit the growth of the hyphal form of Candida albicans. No fungal-growth-inhibitory activity was exhibited for C. albicans by either splenocytes or Percoll-enriched lymphocytes. These cells were capable of cytotoxic activity for a natural killer cell-sensitive cell line. However, when cultured for several days with IL-2, splenocytes acquired the capacity to inhibit the growth of the fungus. The appearance of the antifungal activity coincided with the development of cytotoxic activity for the natural killer cell-insensitive cell line. Anti-C. albicans and antitumor activities of IL-2-activated lymphocytes were competitively and reciprocally inhibited by C. albicans and the natural killer cell-sensitive and -insensitive cell lines. The antifungal activity of the IL-2-activated lymphocytes was exhibited against a number of clinical isolates of C. albicans and related fungal species. IL-2-activated human peripheral blood lymphocytes also acquired the capacity to inhibit the growth of C. albicans. These data show that in vitro growth inhibition can be mediated by IL-2-stimulated lymphocytes which are neither fungal strain nor mammalian species restricted in their biological activity.

Quantitative analysis of opsonophagocytosis and of killing of Candida albicans by human peripheral blood leukocytes by using flow cytometry

We describe a simple, rapid, automated procedure for measuring opsonophagocytosis and killing of Candida albicans by human peripheral blood leukocytes. Yeast cells are labelled by allowing uptake and cleavage of membrane-permeable bis-carboxyethyl-carboxyfluorescein pentaacetoxymethylester to its membrane-impermeable fluorescent derivative bis-carboxyethyl-carboxyfluorescein. The yeast cells are added to cell-rich plasma obtained after dextran sedimentation of erythrocytes. Opsonophagocytosis and killing are quantified by using automated fluorescent cell analysis, and the following parameters can be obtained: (i) relative percentage of phagocytes that participate in opsonophagocytosis, (ii) relative percentage of yeast cells that become associated with phagocytes, and (iii) percentage of killing of C. albicans. The first two parameters are obtained through the additional use of a phycoerythrin-conjugated monoclonal antibody that selectively labels monocytes and polymorphonuclear granulocytes in peripheral blood. Killing is assessed by solubilizing blood cells with deoxycholate to liberate yeast cells from the phagocytes. Viable yeast cells retain carboxyfluorescein, but nonviable cells lose the fluorescent marker; thus, the reduction in number of fluorescent particles directly reflects phagocytic killing. Results obtained by the present method correlated excellently with parallel enumerations by colony counting. Test results with seven healthy individuals revealed a marked dissociation between the process of opsonophagocytosis, which was essentially complete after 20 min at 37 degrees C, and killing rates, which were 48% +/- 11% and 63% +/- 9% (standard deviation) after 1 and 2 h, respectively, when yeast cell-to-phagocyte ratios were in the range of 0.5:1 to 2:1. The described assay is unrivaled in simplicity, rapidity, and reproducibility and generates results for a large number of samples within hours.

Candidacidal activity of Crohn's disease neutrophils

The ability of normal and Crohn's disease neutrophils to kill Candida albicans has been studied using neutrophils isolated from peripheral blood and suspended in phosphate buffered saline at 5 x 10(6) cells per ml. C albicans was grown to a stationary phase in broth culture and suspended in phosphate buffered saline at 10(7) organisms/ml. Neutrophils and Candida were then incubated together at 37 degrees C in a shaking water bath in the presence of fresh serum. At 30 and 60 minutes samples were withdrawn, neutrophils lysed, and Candida survival assessed by colony counting. Results were compared with control suspensions of Candida incubated with serum alone. After 30 and 60 minutes in the presence of autologous serum normal neutrophils had killed significantly more Candida than Crohn's disease neutrophils (mean (SD) 61.0 (16.7)% v 40.5 (16.2)% at 30 minutes, p less than 0.0001; 83.2 (7)% v 70.8) 16)% at 60 minutes, p less than 0.005). The results did not alter significantly when normal neutrophils were incubated with Candida in the presence of Crohn's disease serum instead of normal serum. When Crohn's disease neutrophils were incubated with Candida in the presence of normal serum instead of autologous serum there was some improvement in candidacidal ability at 30 minutes (48.9 (20.6)% v 40.5 (16.2)%, p less than 0.03) but not at 60 minutes. Phagocytosis, measured using a radiometric assay, was normal. Neutrophils from patients with Crohn's disease have an impaired ability to kill this granuloma provoking organism. It is not due to serum inhibitors or defective phagocytosis.

Neutrophil function tests

The complexity of the neutrophil response to inflammation creates many difficulties for the study of neutrophil function in vitro. The environment in which a neutrophil is placed can have marked effects upon a variety of cellular functions. Quantitative tests of neutrophil function present problems not only with assay design but also in the isolation of cells from peripheral blood without disturbing their normal physiology. It is desirable to isolate neutrophils from other leukocytes because soluble factors released by other cells can influence neutrophil function, and other cells may interfere with functional assays; for example, monocytes will phagocytose opsonized particles and eosinophils contain a potent peroxidase. Attention to physical parameters such as temperature, pH or osmolarity, and rigorous exclusion of endotoxin, permits neutrophils to be isolated in a resting state. Subsequent function tests must be selected with an understanding of normal neutrophil physiology and applied with an awareness of any associated technical problems. The investigation of abnormal neutrophil responses may necessitate the screening of several tests of function; for example, defective neutrophil killing may be the result of abnormal chemotaxis, phagocytosis or degranulation. Which tests are appropriate will depend upon the questions to be answered and on the quantity of cells available for study.

Effect of patulin on microbicidal activity of mouse peritoneal macrophages

Patulin, a fungal metabolite shown previously to exert immunosuppressive effects on the cellular and humoral immune systems, was examined for its in vitro effects on some functions of murine peritoneal macrophages. The cells were pre-incubated for 2 hr with mycotoxin concentrations of 0.01-2 micrograms/ml. Phagocytosis and phagosome-lysosome fusion were diminished above 0.1 microgram patulin/ml and lysosomal enzymes and microbicidal activity above 0.5 microgram/ml, whereas O2- production was inhibited only above 2 micrograms/ml. This indicated that the killing mechanism did not depend on products of the oxidative burst. The concentrations used did not decrease the cell viability. Under natural circumstances, patulin may constitute a health risk for animals.

Chronic cough in a hospital population; its relationship to atopy and defects in host defence

The background and aetiology of chronic cough were investigated by comparing 60 children under 6 years with simple cough, 60 children with asthma, and 60 controls. Both cough and asthma were more common in boys and associated with a history of eczema, chest deformity, and skin reactivity to inhaled allergens, but these findings were more prevalent in asthma than cough. House dust mite sensitivity was found in 34 (57%) children with cough, 45 (75%) with asthma, and six (10%) controls. Tests of immunological function showed some high concentrations of IgM in groups with both cough and asthma, but high IgE concentrations, eosinophilia, and lymphocytosis were significant only in asthma. IgG1 and IgG2 concentrations were raised in some children with cough or asthma, but the only low subclass concentrations were of IgG3 observed in the group with cough. Children with simple cough represented a heterogeneous population but many showed evidence of atopy. Major defects of immunity were not observed.

Heat production as a quantitative parameter of phagocytosis

Microcalorimetry was applied to measure phagocytosis by human peripheral blood neutrophils and monocytes. Heat production was 9.1 +/- 2.6 microW by 1 X 10(6) unstimulated neutrophils and increased to 28.4 +/- 3.2 microW in association with phagocytosis. The increase in heat production was directly proportional to the number of Saccharomyces cerevisiae particles phagocytosed as well as to the concentration of opsonizing serum. No heat increase was observed in the absence of phagocytosis. An increase in heat production by monocytes was also observed in association with phagocytosis, but it was much less obvious than that by neutrophils. Heat production can thus be used as a quantitative measure of phagocytosis.

Effects of adenylate cyclase toxin from Bordetella pertussis on human neutrophil interactions with Coccidioides immitis and Staphylococcus aureus

Bordetella pertussis extract that contained adenylate cyclase toxin produced large increases in human neutrophil cyclic AMP levels and inhibited their oxidative burst, as reflected by luminol-enhanced chemiluminescence and superoxide release. The adenylate cyclase toxin-containing extract blocked neutrophil-mediated inhibition of N-acetylglucosamine incorporation by arthroconidia of Coccidioides immitis in a dose-dependent fashion but had no effect on neutrophil phagocytosis of Candida glabrata and only a slight inhibitory effect on arthroconidial attachment. Neither purified pertussis toxin nor extracts from Bordetella mutants lacking the adenylate cyclase toxin affected neutrophil-mediated inhibition of arthroconidial N-acetylglucosamine incorporation. These studies indicate that adenylate cyclase toxin, alone or in concert with other B. pertussis-elaborated toxins, blocks neutrophil inhibition of arthroconidia, primarily by affecting neutrophil responses other than attachment or phagocytosis.

Immunodeficiency due to defects of polymorphonuclear leukocyte function

Functional defects of polymorphonuclear leukocytes can lead to clinical immunodeficiency. Understanding these conditions requires a knowledge of normal polymorph physiology and the means to analyse various aspects of polymorph function. Primary diseases of polymorph function are rare, whereas disorders secondary to other diseases are more common. Prompt diagnosis of these conditions leads to better patient management.

Development of mathematical models for an in vitro-phagocytosis test system

Phagocytosis tests have been carried out by many authors using different methods under different conditions. The results have been interpreted in different ways, as well sometimes with conflicting notations. In order to get to a more systematic data analysis and to separate intrinsic from methodic influences, the possibility to apply mathematical models to a phagocytosis test has been studied. In agreement with previous experiences that phagocytosis can well be represented by a mathematical treatment as Michaelis-Menten-type enzyme kinetics concerning its initial rate and by an exponential function under in vivo conditions, in vitro-phagocytosis was phenomenologically described as an analogon of an irreversible bimolecular chemical reaction. In this way, rate and capacity of phagocytosis may be quantified separately. On the basis of systematic deviations of the data from this model, modifications have been developed which could be connected with pertinent observations. The design of further experiments from preliminary results on the basis of our models is discussed.

A method for measuring rate of neutrophil phagocytosis of Staphylococcus epidermidis or Candida guilliermondii using uptake of tritiated uridine

A method is described for measuring the rate of neutrophil phagocytosis, together with the total and intracellular kill at 20 min of 2 different organisms. The technique is sensitive over the early stages of phagocytosis as it distinguishes between adherent and engulfed organisms and is totally objective. It therefore allows detection of defects in phagocytosis which are missed if only the end point is assessed. Both total and intracellular killing are measured under the same conditions as those used to assess phagocytosis and results obtained on the same day the assay is performed.

A rapid radiometric assay for measuring phagocytosis of Saccharomyces cerevisiae in macrophage cultures

A new assay was developed to measure yeast phagocytosis in cultures of murine resident peritoneal macrophages. Saccharomyces cerevisiae was radiolabeled during exponential growth in nutrient broth supplemented with [3H]glucose. Following ingestion of the radiolabeled heat-killed yeast particles for 15 min, phagocytic capacities were measured in harvested macrophage lysates by liquid scintillation spectrometry. The new procedure compares favorably with light microscopic techniques and appears to be a more sensitive method for quantitating phagocytic function. Dose-response studies indicate, that over a wide range of dexamethasone concentrations, the radiometric procedure consistently measures greater inhibitory effects for the steroid induced suppression of phagocytosis.

Phagocytosis of Mycoplasma pneumoniae and Acholeplasma laidlawii measured as inhibition of [3H]uridine uptake by macrophages

Many studies of the interaction between phagocytes and mycoplasmas have given controversial results. This is probably due both to the small size of the microorganisms and their ability to attach to the cell membrane, making it difficult to distinguish between adsorption and ingestion. To overcome these difficulties we took advantage of a phenomenon we noted occurring concomitantly with phase-contrast microscope-monitored phagocytosis of heat-killed C. albicans, i.e., a reduction of [3H]uridine uptake by macrophages from culture medium. This approach allowed us to measure the ability of mouse peritoneal macrophages and the macrophage-like P 388 D 1 continuous cell line to phagocytose Mycoplasma pneumoniae and Acholeplasma laidlawii. Live, UV-killed and specific antiserum-opsonized mycoplasmas were tested. A. laidlawii was ingested under all the conditions mentioned above, while live M. pneumoniae was not phagocytosed unless UV-killed. Phagocytosis of UV-killed M. pneumoniae was directly verified by transmission electron microscopy studies. Data obtained with opsonized M. pneumoniae indicated no ingestion by mouse peritoneal macrophages and incomplete phagocytosis with P388 D 1 macrophages, suggesting that different responses by different types of phagocytes can be observed. In spite of a lack of information concerning the biological meaning of the inhibition of macrophage RNA metabolism during phagocytosis, our data suggest that this phenomenon may be used to study the phagocytosis of microorganisms which are difficult to visualize.

Intracellular killing of Candida albicans by human polymorphonuclear leucocytes: comparison of three methods of assessment

Three different methods, [3H]uridine uptake, viable count and 51Cr-release were used to assess the intracellular survival of a strain of Candida albicans, 19321, which was lethal for mice injected intravenously. Intracellular survival 1 h after ingestion ranged from 50 to 80% depending on the method employed and the detergent used to lyse the phagocytes. Inhibition of uridine uptake by detergents used to lyse the phagocytes led to difficulty in assessment of intracellular killing by this method.

Rapid microassays of phagocytosis, bacterial killing, superoxide and hydrogen peroxide production by human neutrophils in vitro

Simple, rapid microassays for simultaneous measurement of phagocytosis, bacterial killing, superoxide and hydrogen peroxide production by human neutrophils in vitro are described. All assays employ 96-well flat bottom tissue culture plates which were incubated on a microtitre plate shaker at 37 degrees C. The separate evaluation of ingestion and intracellular killing of E. coli and S. aureus was based on the incorporation of [3H]uridine into viable extracellular bacteria. There was good correlation between plate counts of viable bacteria and amount of radiolabel incorporation. Phagocytosis and killing can be measured in a maximum of 100 microliter reaction mixture, requiring only 2.5 X 10(5) neutrophils per test and the assay is complete within 60 min. Assay of superoxide production by stimulated neutrophils was based on superoxide-dependent reduction of ferricytochrome c as measured spectrophotometrically at 550 nm in wells of tissue culture plates containing 150 microliter of reaction mixture. The assay requires only 1.25 X 10(5) neutrophils per test and is complete within 50 min. Quantitation of hydrogen peroxide was based on horseradish peroxidase-dependent oxidation of phenol red. The technique is as for superoxide detection except that the reaction must be terminated by the addition of 1 M NaOH at the desired time intervals. None of the assays require sampling during the incubation period. The principal advantages of the described techniques are increased simplicity and speed, requirement of low numbers of neutrophils and applicability to analysis of large number of samples in parallel.

A flow cytometric method for the measurement of phagocytosis by polymorphonuclear leucocytes

A new method for the measurement of phagocytosis of Candida albicans by human polymorphonuclear leucocytes (PMN) is described using a fluorescence activated cell sorter. We have used acridine orange to discriminate between PMN which have internalised yeast particles and those which have not. This method allows accurate measurement of particle phagocytosis as an event distinct from particle adherence. It also permits detailed examination of the kinetics of phagocytosis, the study of which is likely to be of value in the investigation of diseases where abnormalities of PMN function are suspected.

A simple and inexpensive method for assessing in vitro candidacidal activity of leukocytes

Candidacidal activity of mouse neutrophils and macrophages was determined directly in microtiter plates. After a suitable period of interaction between phagocytic cells and C. albicans in the wells, the mouse cells were lysed with distilled water and corn meal agar was added to each well. Following incubation at 37 degrees C, viability was assessed using an inverted microscope and counting the number of germ tubes or microcolonies which developed. This method does not use radioisotopes or vital stains and should be applicable to other genera of yeasts.

Defective neutrophil function and microbicidal mechanisms in the myelodysplastic disorders

Neutrophil function studies have been carried out in a series of 44 patients with primary myelodysplastic syndromes (MDS). In vitro tests of phagocytosis and killing of Candida guilliermondii and Staphylococcus aureus identified 13 patients with abnormal neutrophil function at presentation and a further 10 who developed abnormalities during the course of their disease. The incidence of defective function in the five disease categories in this series was: refractory cytopenia (RC) 8/17; refractory cytopenia with sideroblastic change (RC + SC) 5/8; acquired idiopathic sideroblastic anaemia (AISA) 2/4; refractory anaemia with excess blasts (RAEB) 7/11; chronic myelomonocytic leukaemia (CMML) 1/4. Eleven of 23 patients with defective neutrophil function experienced severe infective complications; in only three of these patients were neutrophil counts less than 1 X 10(9)/l and susceptibility to infection was considered to reflect, at least partially, qualitative neutrophil abnormalities. There was no correlation between absolute neutrophil count and defective function. Abnormal overall neutrophil microbicidal activity was equally associated with impaired and normal phagocytosis. Some patients with intracellular killing defects had reduced myeloperoxidase (MPO) activities and one had reduced hexose monophosphate shunt (HMPS) activity. In two patients, whose neutrophils showed markedly impaired candidacidal activity, levamisole corrected function when added in vitro at 10(-7) M and also when administered in therapeutic dosage. It is suggested that deranged function, probably reflecting abnormalities in maturation of the granulocyte series, occurs across the myelodysplastic spectrum and that several microbicidal mechanisms may be defective.

Comparison of the effects of filtration leucapheresis and discontinuous flow centrifugation leucapheresis on granulocyte microbicidal function

In an investigation of the in vitro phagocytic and microbicidal function of granulocytes collected by filtration leucapheresis (FL) from 18 donors and by discontinuous flow centrifugation leucapheresis (DFC) from six donors, comparison was made with the function of granulocytes obtained from the same donors by venepuncture and density gradient centrifugation over Ficoll-Isopaque (FI). No significant impairment of the phagocytosis or killing of Candida guilliermondii by either FL- or DFC-granulocytes was observed. Although the ability of FL-granulocytes to phagocytose and kill Staphylococcus aureus did not differ significantly from the function of control FI-granulocytes, DFC-granulocytes were significantly less active.

A radiolabel release microassay for phagocytic killing of Candida albicans

The chromium release technique for quantifying intracellular killing of radiolabelled Candida albicans particles was exploited in a microassay in which murine and human phagocytes acted as effectors under peculiarly simple conditions. At appropriate effector: target ratios and with a 4 h incubation, up to 50% specific chromium release could be detected in the supernatant with no need for opsonization or lysis of phagocytes. This simple microassay permits easy-to-perform, simultaneous testing of a variety of different phagocytes even if only available in limited amounts, and provides an objective measurement of intracellular killing of Candida albicans.

Polymorph function in asthma

In vitro polymorph movement, phagocytosis and bactericidal activity were compared in asthmatics, patients with bacterial infection and control subject. No gross defects were observed, but statistical analysis indicated that asthmatics have depressed polymorph movement (P less than 0.05) and lower augmentation of an intracellular enzyme activity (NBT reduction), associated with bactericidal function (P less than 0.01). As expected, polymorphs from patients with bacterial infection are capable of increased NBT reduction (P less than 0.001). Correlations between a wide range of clinical and laboratory data were also performed by computer analysis. Among significant findings were indications that atopic extrinsic asthmatics, in comparison with intrinsic asthmatics, have raised unstimulated NBT activity (P less than 0.05) and lower augmentation in response to endotoxin (P less than 0.05), as well as increased IgE and eosinophil counts (P less than 0.002). These findings suggest that in extrinsic asthmatics there may be some impairment of polymorph function which would account for an increased tendency to respiratory infections or to a prolonged recovery from such infections.

Requirement of heat-labile opsonins for maximal phagocytosis of Candida albicans

The requirement for heat-labile opsonins for phagocytosis of 2 serologically distinct strains and a number of clinical isolates of Candida albicans was examined by a previously described radiometric technique. The results indicated that both strains and all 10 isolates of C. albicans examined required heat-labile opsonins for maximal phagocytosis. The data suggest that heat-labile opsonins play an important role in immunity to C. albicans. However, the possibility that some strains of C. albicans may not utilize heat-labile opsonins cannot be excluded.

Effect of bilirubin on the fungicidal capacity of human neutrophils

The effect of unconjugated bilirubin on the fungicidal capacity of human neutrophils was examined. Per cent Torulopsis glabrata killed in the presence of 1 x 10(-5) and 5 x 10(-5) M bilirubin was 72.7 +/- 2.5 and 40.9 +/- 7.2 respectively, compared to 81.4 +/- 4.1 in control (p less than 0.01 and p less than 0.001), respectively). This effect was not due to a concomitant inhibition of phagocytosis. The results suggest that jaundiced neonates may be more susceptible to fungal infections.

Activation of the alternative complement pathway by Torulopsis glabrata

Torulopsis glabrata is a yeast-like fungus with increasing importance as an opportunistic human pathogen. The role of serum complement in resistance to this infection was studied by chemotactic and opsonic assays. The results indicate that T. glabrata activates complement via the alternative pathway. This may be an important mechanism in host immunity to this fungus.

A micro method for the estimation of killing and phagocytosis of Candida albicans by human leucocytes

A micro method is described for quantitation of the candidacidal and phagocytic capacity of human neutrophils based on previous studies which showed that non-viable Candida albicans are differentially stained by methylene blue. The assay was performed on a microplate using small numbers of phagocytes (2 x 10(3) per well) and Candida albicans (2 x 10(3) or 8 x 10(3) per well) and both the phagocytic and microbicidal activity could be observed in situ within the phagocytic cell. The technique requires small volumes of blood (2 ml) and simple apparatus. Plates may be stored after fixation of stained preparations which makes it particularly suitable as an initial screen of phagocyte function for routine clinical use.

Participation of C3 in intracellular killing of Candida albicans

Using new objective methods for measuring, independently, phagcytosis and killing, it was demonstrated that Candida albicans opsonized by C3-deficient serum was ingested by not killed in vitro by human polymorphonuclear leukocytes. Killing could be induced by adding purified C3 to the C3-deficient serum. It is concluded that C3 participates directely in the intracellular process leading to phagocytic killing of C. albicans.