Monocyte phagocytosis of opsonizedNeisseria meningitidisserogroup B

Flow cytometry technique for analysing Leishmania promastigote phagocytosis by human polymorphonuclear leucocytes and monocytes

In this study, we developed a flow cytometry technique for studying Leishmania (L.) mexicana phagocytosis by human polymorphonuclear leucocytes (PMNs) and monocytes. Leishmania promastigotes are elongated in shape and flagellated. This influences the light scatter when phagocytosis is measured by flow cytometry. Accordingly, we developed an oxidative burst method for measuring the phagocytic process. As this is an indirect marker of phagocytosis, we used confocal, light and electron microscopy to verify that promastigotes were, indeed, internalized by the phagocytes. For both PMNs and monocytes, the optimal conditions for achieving high sensitivity in flow cytometry detection were 5% pooled human serum and 15 min. incubation time. Incubations at 35, 37 and 39°C were also equally efficient for both PMNs and monocytes. Optimal parasite ratios were 10 parasites per PMN and 20 parasites per monocyte. Under these conditions, Leishmania were readily phagocytosed by human PMNs and monocytes and the effects of other influences, such as treatment, would be readily detectable. This indicated that these cells may play a role in the immune response against Leishmania.

Flow cytometric quantitative determination of ingestion by phagocytes needs the distinguishing of overlapping populations of binding and ingesting cells

BACKGROUND

The use of flow cytometry with fluorescently labeled particles provides the means to examine quantitatively the phagocytotic capacity of an individual phagocyte. This report describes an improved flow cytometric method of analysis for kinetic measurement of phagocytosis of fluorescein isothiocyanate (FITC)-labeled zymosan particles by human leukocytes.

METHODS

FITC-labeled zymosan was incubated with leukocyte suspension, and at selected time intervals fluorescence positive neutrophils were divided by phagocytotic gates into three subpopulations: neutrophils that were neither binding nor ingesting particles, neutrophils that were only binding particles (binding cells), and neutrophils that were binding and ingesting particles (ingesting cells). For the distinction between internalized and surface-bound FITC-labeled zymosan, trypan blue (1.2 mg/ml) was used to quench surface-bound fluorescence.

RESULTS

The technical challenges related to settings of phagocytotic gates and derivation of phagocytotic equations were presented. From 28 control samples, numerical values of mean fluorescence intensities and percentages of phagocytotic subpopulations inside phagocytotic gates before and after quenching were inserted into phagocytotic equations and corrected phagocytotic parameters were calculated. Calculated parameters were surprisingly constant across individuals.

CONCLUSIONS

Essential elements of the present method appeared to be partial quenching of extracellular fluorescence with trypan blue and distinguishing between overlapping populations of binding and ingesting cells. Corrections using derived phagocytotic equations proved necessary for accurate kinetic phagocytotic measurements. Corrections were less necessary when the ingestion process was finished.

The infant rat model adapted to evaluate human sera for protective immunity to group B meningococci

The infant rat infection model previously developed to evaluate protective ability of passively administered murine antibodies to group B meningococcal (MenB) surface antigens was adapted for human sera. Several challenge doses were tested, aiming at sensitive detection of protection with little interassay variability. Doses of 10(5) and 10(6) colony forming units of strain IH5341 (MenB:15:P1.7,16) injected intraperitoneally gave consistently high levels of bacteremia and meningitis developed in 6 h in 50-100% of the pups. A monoclonal antibody mAb735 to the MenB capsule, injected 1-2 h before bacterial challenge, gave full protection at a dose of 2 microg/pup. Sera from adult volunteers immunized with a MenB outer membrane vesicle vaccine reproducibly reduced bacterial counts in the blood and cerebrospinal fluid, whereas a normal human serum, lacking bactericidal and opsonophagocidal activity, was unprotective.

Survival and function of phagocytes in blood culture media

The survival and function of human phagocytes in sterile aerobic and anaerobic blood culture media were investigated using neutrophil morphology, white blood cell count in a haemoanalyser, flow cytometry, oxidative burst response, and bactericidal effect in Colorbact and Septi-Chek blood culture media and Bact/Alert. When comparing agitation to stationary incubation no difference in phagocytic activity was found. The methods showed the same trends demonstrating that the phagocytes' viability and activity were prolonged by oxygen and shortened by anaerobic conditions and sodium polyethanol sulfonate (SPS). Best preserved activity and viability were found in the aerobic media containing less than 0.5 g/l SPS, in which significant phagocyte oxidative burst and bactericidal activity were found up to 4 days after inoculation. Considering that the majority of bacteremias are due to aerobic or facultatively anaerobic bacteria, the present data suggest that most bacteria may be recovered by the use of one aerobic bottle with SPS concentration below 0.5 g/l to protect meningococci and other SPS-sensitive bacteria and one above 0.5 g/l to stop phagocytic activity, plus one anaerobic bottle with SPS below 0.5 g/l.