Fixation and long-term storage of human lymphocytes for surface marker analysis by flow cytometry

Comparative flow cytometry-based immunophenotyping analysis of peripheral blood leukocytes before and after fixation with paraformaldehyde

Flow cytometry based immunophenotyping provides prime insight into cellular population composition and characteristics, and is widely used in basic and clinical research. Challenges in processing peripheral blood samples in a timely manner necessitate protocol adaptations and utilization of fixatives. Fixation, however, may introduce artifacts to the flow cytometry readout. We performed a comparative flow cytometry immunophenotyping analysis of 13 immune cell populations in the whole blood using a staining protocol with and without fixation step. Freshly procured human peripheral blood samples were stained with a panel of 33 fluorochrome-conjugated antibodies. Samples were processed using a protocol with or without a paraformaldehyde-based fixation step, and matching sample pairs were analyzed by flow cytometry. Our results show that paraformaldehyde-based fixation, in comparison to matched unfixed samples, did not significantly affect population distribution and frequency for: B cells, Plasmablasts, Dendritic cells, NK cells, Granulocytes, Neutrophils, Eosinophils, or Hematopoietic Stem/Progenitor Cells. However, fixation led to significant marker shifts in the subpopulation distribution in CD4, T regulatory, CD8, Monocytes, and Basophils. These results indicate the importance of pre-experimental assessment of fixation-introduced artifacts in the flow cytometry output when considering the feasibility of fresh processing. This is especially important for samples analyzed using comprehensive exploratory immunoprofiling panels.

From nasal to basal: single-cell sequencing of the bursa of Fabricius highlights the IBDV infection mechanism in chickens

BACKGROUND

Chickens, important food animals and model organisms, are susceptible to many RNA viruses that invade via the nasal cavity. To determine the nasal entry site of the virus and clarify why avians are susceptible to RNA viruses, infectious bursal disease virus (IBDV) was selected because it is a typical avian RNA virus that infects chickens mainly via the nasal route.

RESULTS

First, we found that IBDV infected the posterior part of the nasal cavity in chickens, which is rich in lymphoid tissue and allows the virus to be easily transferred to the blood. Via the blood circulation, IBDV infected peripheral blood mononuclear cells (PBMCs) and was transferred to the bursa of Fabricius to damage the IgM + B lymphocyte population. Subsequently, the single-cell RNA sequencing (scRNA-seq) results suggested the more detailed response of different bursal cell populations (B cells, epithelial cells, dendritic cells, and fibroblasts) to IBDV. Regarding B cells, IBDV infection greatly decreased the IgM + B cell population but increased the IgA + B cell population in the bursal follicles. In contrast to B cells, bursal epithelial cells, especially basal cells, accumulated a large number of IBDV particles. Furthermore, we found that both innate RNA sensors and interferon-stimulated genes (ISGs) were highly expressed in the IBDV-infected groups, while dicer and ago2 expression was largely blocked by IBDV infection. This result suggests that dicer-related RNA interference (RNAi) might be an effective antiviral strategy for IBDV infection in avian.

CONCLUSION

Our study not only comprehensively elaborates on the transmission of airborne IBDV via the intranasal route and establishes the main target cell types for productive IBDV infection but also provides sufficient evidence to explain the cellular antiviral mechanism against IBDV infection.

Investigation of the response of tear-film neutrophils to interleukin 8 and their sensitivity to centrifugation, fixation, and incubation

During eye closure, a large number of neutrophils (polymorphonuclear neutrophils, PMNs) invade the ocular surface and are often referred to as tear-film PMNs. While immunophenotyping experiments have been performed on tear-film PMNs, the impact of commonly used experimental procedures on their phenotype as well as their response to interleukin-8 (IL-8), a physiological inflammatory mediator, have not yet been investigated. A gentle eye wash method was used to collect cells at home. In the morning upon awaking, participants washed their eyes with sterile phosphate buffer saline (PBS) and collected the runoff into a sterile polypropylene tube. The cell collection was then delivered to the lab within two hours. The effects of centrifugation, incubation and fixation with paraformaldehyde (PFA) before (pre-fixed staining) or after (post-fixed staining) incubation with antibodies were characterized. Tear-film PMNs as well as blood PMNs (used for comparison) were also stimulated with IL-8. To assess the reproducibility of cell collection and variability in receptor expression over time, participants were also asked to collect cells three times over a period of a month. The change in expression of surface receptors, CD11b, CD16, CD55, CD66b, important inflammatory and activation markers, and CD45 (PAN leukocyte marker) was assessed by flow cytometry. Fixing tear-film PMNs prior to the staining with antibodies resulted in a significant (fivefold or more) reduction in the expression of CD11b, CD16 and CD45 when compared to unfixed samples, while CD16 was the only receptor to undergo significant downregulation upon post-staining fixation. Furthermore, additional centrifugation step prior to antibody incubation as well as long (4 h) incubation at 37 °C resulted in significant reductions in expression of CD11b, CD16 and CD55 when compared to control samples. As opposed to blood PMNs, stimulating tear-film PMNs with IL-8 did not induce any significant changes in expression of CD11b, CD16, CD55 and CD66b. When working with collected tear-film PMNs, our results suggest that any additional centrifugation and incubation step should be avoided, or at least limited, and post fixation staining is recommended in order to preserve cell phenotype and cell integrity of tear film PMNs. Our study also adds further information on the reproducibility of the gentle eye wash as well as the inability of tear-film PMNs to modulate their surface receptors upon stimulation with IL-8. The latter may be due to prior exposure to IL-8, activation in the closed-eye environment, or a reduced ability to respond to inflammatory stimulus. Further mechanistic studies will be needed to gain a better understanding of the tear-film neutrophil phenotype.

Whole blood flow cytometry protocol for the assessment of platelet phenotype, function, and cellular interactions

Platelets are a key component of the hemostatic system and their roles in inflammation via interactions with leukocytes have also gained attention in recent years. Changes in platelet phenotype and function can cause bleeding and/or thrombosis and, as such, monitoring platelet-specific changes is crucial to assessing hemostasis in the clinical setting. Currently, available platelet function tests such as platelet aggregometry and thromboelastography require a large volume of blood, which is a major limitation for the pediatric population. Whole blood flow cytometric analysis of platelets is increasingly utilized in recent years, primarily due to the sensitivity of this method, but also because it only requires a small amount of blood with minimal sample manipulation. We have developed a whole blood flow cytometry methodological approach that enables the assessment of platelet phenotype, function, and their interactions with monocytes and neutrophils.

Reliable cerebrospinal fluid cytology reporting over an extended period: Is it possible by adding formol saline and ethylenediaminetetraacetic acid as cell preservative?

BACKGROUND

Reporting cerebrospinal fluid (CSF) cytology within a narrow time frame is crucial as it is often indicated in critically ill patients and moreover, the cells in CSF are highly labile and tend to decline rapidly on standing. However, due to various logistic issues, delay in reporting is inevitable at times, especially if ancillary tools are required. In this study, we examine the effect of using formol saline and ethylenediaminetetraacetic acid (EDTA) as a preservative on the cellular composition of CSF at 18, 24, and 48 hours of preservation.

METHODS

Thirty CSF specimens were examined within 2 hours of collection and this reading was recorded as time zero reading. The CSF specimens were then divided in three tubes with: (a) preservative:CSF ratio of 1:1; (b) preservative:CSF ratio of 1:5; and (c) no preservative. Total and differential leucocyte counts and immunocytochemistry were performed on the three specimens at 18, 24, and 48 hours and were compared with the readings at 0 hour.

RESULTS

Preserved CSF (in the ratio of 1:5) showed no significant decrease in the number of cells at 18 hours (P = .4), 24 hours (P = .3), and 48 hours (P = .1). Cellularity decreased by 8.5%, 22%, and 40% at 18, 24, and 48 hours, respectively. Cell morphology and antigenicity were well preserved at all the three time intervals.

CONCLUSION

Formol saline and EDTA, when mixed with the CSF in the ratio of 1:5, can preserve significant cellularity for up to 24 hours.

Optimized protocols for isolation, fixation, and flow cytometric characterization of leukocytes in ischemic hearts

Immune activation post-myocardial infarction is an orchestrated sequence of cellular responses to effect tissue repair and healing. However, excessive and dysregulated inflammation can result in left ventricular remodeling and pathological alterations in the structural and mechanical attributes of the heart. Identification of key pathways and critical cellular mediators of inflammation is thus essential to design immunomodulatory therapies for myocardial infarction and ischemic heart failure. Despite this, the experimental approaches to isolate mononuclear cells from the heart are diverse, and detailed protocols to enable maximum yield of live cells in the shortest time possible are not readily available. Here, we describe optimized protocols for the isolation, fixation, and flow cytometric characterization of cardiac CD45⁺ leukocytes. These protocols circumvent time-consuming coronary perfusion and density-mediated cell-separation steps, resulting in high cellular yields from cardiac digests devoid of contaminating intravascular cells. Moreover, in contrast to methanol and acetone, we show that cell fixation using 1% paraformaldehyde is most optimal as it does not affect antibody binding or cellular morphology, thereby providing a considerable advantage to study activation/infiltration-associated changes in cellular granularity and size. These are highly versatile methods that can easily be streamlined for studies requiring simultaneous isolation of immune cells from different tissues or deployment in studies containing a large cohort of samples with time-sensitive constraints.NEW & NOTEWORTHY In this article, we describe optimized protocols for the isolation, fixation, and flow cytometric analysis of immune cells from the ischemic/nonischemic hearts. These protocols are optimized to process several samples/tissues, simultaneously enabling maximal yield of immune cells in the shortest time possible. We show that the low-speed centrifugation can be used as an effective alternative to lengthy coronary perfusion to remove intravascular cells, and sieving through 40-μm filter can replace density-mediated mononuclear cell separation which usually results in 50-70% cell loss in the sedimented pellets. We also show that cell fixation using 1% paraformaldehyde is better than the organic solvents such as methanol and acetone for flow cytometric analysis.

Impact of blood storage and sample handling on quality of high dimensional flow cytometric data in multicenter clinical research

Obtaining reliable and reproducible high quality data in multicenter clinical research settings requires design of optimal standard operating procedures. While the need for standardization in sample processing and data analysis is well-recognized, the impact of sample handling in the pre-analytical phase remains underestimated. We evaluated the impact of sample storage time (≈transport time) and temperature, type of anticoagulant, and limited blood volume on reproducibility of flow cytometric studies. EDTA and Na-Heparin samples processed with the EuroFlow bulk lysis protocol, stained and stored at 4 °C showed fairly stable expression of cell surface markers and distribution of the major leukocyte populations for up to 72 h. Additional sample fixation (1% PFA, Fix & Perm) did not have any beneficial effects. Blood samples stored for <24 h at room temperature before processing and staining seemed suitable for reliable immunophenotyping, although losses in absolute cell numbers were observed. The major losses were observed in myeloid cells and monocytes, while lymphocytes seemed less affected. Expression of cell surface markers and population distribution were more stable in Na-Heparin blood than in EDTA blood. However, storage of Na-Heparin samples was associated with faster decrease in leukocyte counts over time. Whole blood fixation strategies (Cyto-Chex, TransFix) improved long-term population distribution, but were detrimental for expression of cellular markers. The main conclusions from this study on healthy donor blood samples were successfully confirmed in EDTA clinical (patient) blood samples with different time delays until processing. Finally, we recognized the need for adjustments in bulk lysis in case of insufficient blood volumes. Despite clear overall conclusions, individual markers and cell populations had different preferred conditions. Therefore, specific guidelines for sample handling should always be adjusted to the clinical application and the main target leukocyte population.

Effects of Decade Long Freezing Storage on Adipose Derived Stem Cells Functionality

Over the last decade and half, the optimization of cryopreservation for adipose tissue derived stromal/stem cells (ASCs) especially in determining the optimal combination of cryoprotectant type, cooling rate, and thawing rate have been extensively studied. In this study, we examined the functionality of ASCs that have been frozen-stored for more than 10 years denoted as long-term freezing, frozen within the last 3 to 7 years denoted as short-term freezing and compared their response with fresh ASCs. The mean post-thaw viability for long-term frozen group was 78% whereas for short-term frozen group 79% with no significant differences between the two groups. The flow cytometry evaluation of stromal surface markers, CD29, CD90, CD105, CD44, and CD73 indicated the expression (above 95%) in passages P1-P4 in all of the frozen-thawed ASC groups and fresh ASCs whereas the hematopoietic markers CD31, CD34, CD45, and CD146 were expressed extremely low (below 2%) within both the frozen-thawed and fresh cell groups. Quantitative real time polymerase chain reaction (qPCR) analysis revealed some differences between the osteogenic gene expression of long-term frozen group in comparison to fresh ASCs. Intriguingly, one group of cells from the short-term frozen group exhibited remarkably higher expression of osteogenic genes in comparison to fresh ASCs. The adipogenic differentiation potential remained virtually unchanged between all of the frozen-thawed groups and the fresh ASCs. Long-term cryopreservation of ASCs, in general, has a somewhat negative impact on the osteogenic potential of ASCs, especially as it relates to the decrease in osteopontin gene expression but not significantly so with respect to RUNX2 and osteonectin gene expressions. However, the adipogenic potential, post thaw viability, and immunophenotype characteristics remain relatively intact between all the groups.

NOD-like receptors mediated activation of eosinophils interacting with bronchial epithelial cells: a link between innate immunity and allergic asthma

Key intracytosolic pattern recognition receptors of innate immunity against bacterial infections are nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs). We elucidated the NOD1 and NOD2-mediated activation of human eosinophils, the principal effector cells for allergic inflammation, upon interacting with human bronchial epithelial BEAS-2B cells in allergic asthma. Eosinophils constitutively expressed NOD1,2 but exhibited nonsignificant responses to release chemokines upon the stimulation by NOD1 ligand γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) and NOD2 ligand muramyl dipeptide (MDP). However, iE-DAP and MDP could significantly upregulate cell surface expression of CD18 and intercellular adhesion molecule (ICAM)-1 on eosinophils and ICAM-1 on BEAS-2B cells, as well as induce chemokines CCL2 and CXCL8 release in the coculture system (all P<0.05). Both eosinophils and BEAS-2B cells were the main source for CXCL8 and CCL2 release in the coculture system upon iE-DAP or MDP stimulation. Direct interaction between eosinophils and BEAS-2B cells is responsible for CCL2 release, and soluble mediators are implicated in CXCL8 release. ERK and NF-κB play regulatory roles for the expression of adhesion molecules and chemokines in coculture. Treatment with NOD1,2 ligand could induce the subepithelial fibrosis and significantly enhance the serum concentration of total IgE, chemokine CCL5 for eosinophils and T helper type 2 (Th2) cells and asthma Th2 cytokine IL-13 in bronchoalveolar lavage fluid of ovalbumin-sensitized allergic asthmatic mice (all P<0.05). This study provides further evidence of bacterial infection-mediated activation of NOD1,2 in triggering allergic asthma via the activation of eosinophils interacting with bronchial epithelial cells at inflammatory airway.

Modifications in flow cytometric estimation of t cell subsets and b cells in peripheral blood to reduce the cost of investigation

The development of monoclonal antibodies combined with flow cytometry has revolutionized the analysis of lymphocyte subsets. These newer methods using the Q-prep leucocyte preparation system require only 1-2 ml of blood as compared to 10 ml required traditionally. One of the main impediments in the use of this superior technology in Indian laboratories has been the high cost of reagents. This study evaluated methods to reduce the cost of assays. In the first experiment from 26 healthy subjects, 2ml venous blood samples in EDTA (ethylenediamine tetra-acetate) were obtained. Each sample was divided into two equal portions, one portion was stained using diluted monoclonal antibody, whereas the other portion was stained using standard concentrations of antibodies. In the second experiment, blood samples from 12 subjects were again divided into 2 portions; one portion of each pair was processed using commercial Q-prep reagents while the other portion was processed using our own reagents. In the first experiment, which evaluated use of a diluted antibody against the standard recommended concentrations, a 5-tube panel that estimated CD3, CD4, CD8, CD20 was used. In the second experiment CD3, CD4 and CD8 were estimated. The total cost per sample for a 5-panel estimation was however reduced from $39.11 to $1.10.Given the proven advantages of using a whole blood stain-lyse method for T cell subset estimations, its use should be encouraged in developing country settings. With the suggested methods the whole blood Q-prep could be performed at appreciably reduced costs, without loss in precision.

The effect of shark liver oil on the tumor infiltrating lymphocytes and cytokine pattern in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Shark Liver Oil (SLO) is a traditional medicine that has been widely used in Scandinavian folk to augment the immune response in some immune-related diseases, especially as an anti-cancer agent.

AIM OF THE STUDY

The object of this project was to confirm the anti-cancer effect of SLO and the possible involving mechanisms.

MATERIALS AND METHODS

Using delayed-type hypersensitivity (DTH) response in normal mice, the optimal dose for stimulation of cellular immunity was obtained and injected intraperitoneally to the tumor-bearing mice. Cytokine pattern of splenic MNCs was tested by ELISA. The percentage of CD(4)(+) and CD(8)(+) lymphocytes in tumor-infiltrating lymphocytes was determined by flow cytometry. Also the rate of increase in tumor volume measured.

RESULTS

Our findings indicated that SLO highly augments delayed-type hypersensitivity response against sheep Red Blood Cell (sRBC) in mice. Furthermore, intraperitoneal injection of SLO to tumor-bearing mice could increase T-cell infiltration into the tumor and lower the increasing rate of tumor's volume. Also, it changes the cytokine pattern of the splenic Mononuclear cells (MNCs) to Th1.

CONCLUSION

Increase in IFN-gamma (resulting in enhanced cellular immunity) and increase in especially CD(8)(+) lymphocytes accompanied by a decrease in tumor size are among the signs of its anti-tumor effect. Accordingly, we suppose that SLO is a good candidate for further studies in cancer therapy.

Changes in fluorescence intensity of selected leukocyte surface markers following fixation

BACKGROUND

Immunophenotyping of blood leukocytes often involves fixation with paraformaldehyde prior to cytometry analysis. However, the influence of cell type and marker specificity on the stability of fluorescence intensity after fixation has not been well studied.

METHODS

Human whole blood was stained using a panel of fluorescein isothiocyanate-labeled antibodies to surface markers. Unfixed and fixed samples were analyzed by flow cytometry at 0, 2, 4, 6, 24, 48, and 96 h after staining. Fluorescence measurements were converted to molecules of equivalent soluble fluorochrome for comparison.

RESULTS

Fixation caused a significant decrease in both forward and side scatter at 48 h which required gating adjustments to achieve resolution of cell populations. The autofluorescence increased progressively in fixed samples (ninefold at 96 h for monocytes). Variable decreases in marker-associated fluorescence became apparent after correction for autofluorescence. The magnitude of the decrease at 96 h varied with cell type and marker, from 5% for CD32 on monocytes to 39% for CD16 on neutrophils.

CONCLUSION

The change in fluorescence intensity following staining and fixation of leukocytes varies with cell type and surface marker. Fluorescence stability should be determined for each cell type and marker used, and the confounding effects of fixation on cell autofluorescence should be considered.

Low molecular weight fraction of shark cartilage can modulate immune responses and abolish angiogenesis

Shark cartilage has proven to have inhibitory effects on angiogenesis. In this research, we studied the effects of shark cartilage on the immune system. Firstly, we isolated and purified a shark cartilage protein fraction with the most immunostimulatory effects. Our fraction was composed of two proteins with molecular weights of about 14 and 15 kDa. This fraction highly augments delayed-type hypersensitivity response against sRBC in mice, and decreases the cytotoxic activity of Natural Killer cells. Furthermore, intraperitoneal injection of this fraction to tumor-bearing mice could increase T-cell infiltration into the tumor, and decrease the tumor lesion size. Also, this fraction has strong inhibitory effect on HBMEC proliferation and migration in fibrin matrix. According to these results, we suppose that this fraction is a good candidate for further studies in cancer therapy.

Modulation of CD(4)(+) and CD(8)(+) tumor infiltrating lymphocytes by a fraction isolated from shark cartilage: shark cartilage modulates anti-tumor immunity

Shark cartilage has proven to have some inhibitory effects on angiogenesis, metastasis, cell adhesion and proteolysis. In this study, we wanted to study some of the effects of shark cartilage on tumor immune response. Firstly, by means of chromatographic methods and delayed type hypersensitivity (DTH) test, we optimized a procedure for isolation and purification of a shark cartilage protein fraction with most immunostimulatory effects. Then, we examined its effect on the infiltration of CD(4)(+) and CD(8)(+) lymphocytes into a murine tumor model. Our fraction was composed of two major proteins with molecular weights (MWs) of about 14 and 15 kDa. This fraction highly increases DTH response against sRBC in mice. Furthermore, intraperitoneal injection of this fraction to tumor-bearing mice could increase T-cell infiltration into the tumor. Also, there was a significant increase in the CD(4)/CD(8) ratio in tumor infiltrating lymphocytes, but no such changes were found in the peripheral blood lymphocytes. According to these results, we suppose that this fraction is a good candidate for further studies in cancer therapy. Also, we concluded that this fraction, with previously proven anti-angiogenic effects, can augment cellular immune response and T-cell infiltration into the tumor and thus, there may be a direct relationship between angiogenesis inhibition and T-cell infiltration.

Stability of fresh and preserved fetal and adult lymphocyte cell surface markers

Delay between blood collection and immunophenotyping of peripheral blood (PB) and umbilical cord blood (UCB) lymphocytes occurs frequently. Holding media address this problem, but there are few reports of their limitations. We tested the ability of Cyto-Chex (CC) to preserve the ability of lymphocyte subpopulations to be immunophenotyped after time delays. Ten UCB and 10 PB specimens were kept up to 48 hr and then placed in CC for 1 week, with removal of aliquots for staining with CD3, CD4, CD8, CD19, and CD45 at intervals. There were no significant changes in the number of nonpreserved PB or UCB cells stained with any of the reagents after 48 hr. Aside from a small decrease in UCB B-cell numbers, there were no changes in UCB or PB lymphocyte numbers after placing them in CC for 1 week. However, PB and UCB CD19+ cells and CD8+ T cells lost capacity for bright staining after 1 week in CC. The results suggest that UCB and PB can be held for up to 48 hr before being placed in CC and then kept for up to 1 week in CC with no decrease in T-cell numbers and only a minor reduction of B-cell numbers, albeit with a marked reduction in staining intensity.

Preparation of cells from blood

Peripheral blood is a bountiful source of numerous cell types that are easily analyzed by flow cytometry for a variety of properties. The monodisperse nature of blood makes preparation of these cells relatively easy if the coagulation cascade is inhibited. For some studies the presence of serum can be a confounding factor, although this is often overcome by merely pelleting the cells from the serum and washing the remaining cells several times. Blood, particularly from humans and primates, should be considered highly infectious whether or not from a healthy donor. Therefore universal precautions should be followed at all times. Techniques and route of collection may have a profound influence on the condition and nature of the blood being obtained. Performing venipuncture with an extremely small gauge needle may disrupt cells and prevent satisfactory analysis. Venous blood and arterial blood may yield differing data. Even blood collection at different times of day may yield diurnal variations in some assays. The demands of each cell type and of each assay dictate specific preparation, fixation, storage, and staining protocols. However, the overall goal for preparation of cells from blood, for all of the assays, remains the same--collect and prepare the cells in such a manner that they accurately represent the in vivo state.

Relationship between serum prolactin, lactation and changes in maternal blood B-cell (CD19+) percents during the first 8 months post-partum

Lactation is an immunologically unique state when immune factors are produced by the mother for the protection of the infant rather than the mother. While several studies have focused on the immunological composition of human milk, much less information is available on maternal immune status during lactation. Sixty-four lactating and 43 bottle-feeding women at 1-2 weeks, 1, 2, 4 or 8 months post-partum were studied in a cross-sectional design, with 14 nulliparous women as controls. Flow cytometry analysis of peripheral blood lymphocytes showed dynamic, post-partum changes in the B-cell subpopulation. Among lactating women, the relative percents of CD19+ B-cells were significantly lower (P < 0.05) than control levels at 1-2 weeks and 1 month post-partum, but showed a significant, polynomial-linear rise (P < 0.05) over time, reaching control values by 2-4 months post-partum. Bottle-feeding women had an earlier rise in the percentage of CD19+ cells, with relative percents always significantly higher than their lactating counterparts. The differing patterns may be due to changes in serum prolactin concentrations because, among the post-partum women, relative percents of CD19+ cells were negatively correlated with baseline serum prolactin concentrations. These results have implications for maternal immunization programs designed to enhance maternal and/or infant well-being as well as other maternal health effects related to breastfeeding.

Flow cytometric analysis of bovine CD4 and CD8 lymphocytes: influence of blood sampling and processing methods

Technical information to facilitate bovine blood treatment for optimum lymphocyte flow cytometry analysis is reported. Murine monoclonal antibodies CC8 and CC63 were used to identify phenotypes corresponding to bovine CD4 T cells and CD8 T cells. Blood samples collected in acid citrate dextrose (ACD) enhanced leucocyte subpopulation separation compared with ethylenediamine tetra-acetic acid, heparin and sodium citrate. To preserve bovine blood before immunophenotyping, samples collected in ACD may be kept at 22 degrees C or at 4 degrees C and should be analysed within 32 hours. For isolation of white blood cells, whole blood lysis was faster and gave the same results as Ficoll gradient separation 1.077 and Ficoll gradient separation 1.083. After immunophenotyping, blood could be stored at 4 degrees C if fixed with paraformaldehyde within seven days. Owing to diurnal variations, blood should be collected at a standard time of the day.

Preservation of B-cell-associated surface antigens by chemical fixation

Usual methods of chemical fixation preclude examination of cells with most monoclonal antibodies due to alteration or destruction of the surface antigen itself. A method of chemical stabilization and preservation of human B-cell-associated surface antigens is described which facilitates retrospective flow cytometric analysis. This method involves pretreatment of the cells with protease enzyme inhibitors, followed by chemical cross-linking of surface proteins with 2% formalin, and finally blockade of non-specific reactive groups with excess glycine. Once prepared, the expression of pertinent cellular antigens is stable on the cell surface for as long as 4 years. Such methodology could conceivably be used for preparation of cells for longitudinal quality control of monoclonal antibodies or archival storage of patient specimens for retrospective flow cytometric analysis.

Human T lymphotropic virus type II (HTLV-II) infection among female prostitutes in Yucatan, Mexico

The antibodies to human T-lymphotropic virus type I/II (HTLV-I/II) were determined in non-intravenous drug-using female prostitutes from Merida Yucatan, Mexico. Serum specimens from 282 female prostitutes collected during 1990 were tested initially by enzyme immunoassay and further confirmed by western blot assays. Of these, 5 (1.8%, 95% confidence interval 0.2 to 3.3) were shown to be HTLV-I/II positive (reactivity to p24gag and gp68/r21eenv). All five specimens were shown to be infected with HTLV-II by immunoassays using type-specific synthetic peptides and recombinant proteins. Long-term cell lines developed from two individuals demonstrated active viral replication and were of CD8 phenotype. Polymerase chain reaction analysis from four of these five prostitutes demonstrated HTLV-II-specific amplification of all four specimens, of which one was subtype a (HTLV-IIa) and three were subtype b (HTLV-IIb). These data show that HTLV-II is the predominant HTLV type among female prostitutes from the Yucatan.

Abnormal response to IL-5 in B-cell chronic lymphocytic leukemia

In B-cell chronic lymphocytic leukemia, neoplastic B-lymphocytes are arrested in development. Since interleukins are essential for B-cell differentiation, we examined whether B-CLL cells were capable of responding normally to interleukins. Purified B-lymphocytes from B-CLL patients and controls were compared for their ability to proliferate and differentiate after stimulation with MCAT or SAC plus rhIL-2 or rhIL-5. When rhIL-5 was added to MCAT-stimulated cells, 8 of 10 controls showed a substantial increase in IgM production, compared with only 1 of 10 B-CLL patients. Lack of IL-5 responsiveness could provide insight into the arrested B-lymphocyte development of some B-CLL patients.

Flow cytometric clonal excess analysis of peripheral blood, routine handling, and pitfalls in interpretation

Clonal excess (CE) analysis by flow cytometry is a convenient method to detect minimal involvement of peripheral blood and bone marrow by B-cell lymphoma. The method is based on evaluation of the congruity between kappa and lambda light chain distributions within a normal B-cell population. By using the Kolmogorov-Smirnov method for evaluation of histogram identity, the maximum difference (D value) between distributions is calculated. However, variable adsorption of cytophilic plasma immunoglobulin (Ig) to CD16 positive cells, T-cell subsets, and the B cells themselves may cause incongruity between the light chain distributions that might simulate or disguise a true clonal excess and thus create major pitfalls in the interpretation of the CE analysis. These phenomena are observed both in normal blood donors and in patients with non-Hodgkin's lymphoma. In the present report we describe: (1) how freezing of the isolated mononuclear cells before immunostaining effectively removes most of the adsorbed cytophilic Ig, (2) how by exclusion of the CD16 positive population further resolution of the relevant histogram shape is obtained to avoid false interpretations of incongruity, and (3) how adsorption of Ig to B-cells creates a typical pattern of "reciprocal labeling" that can be mistaken for a clonal excess. Based on our observations we argue against an uncritical use of normal D values for definition of clonal excess and advocate an analytic evaluation of the kappa and lambda overlay distribution by dual immunofluorescence, either by excluding CD16 positive cells or by including only B cells, to reveal the nature of the different deviations.

Treatment of Rheumatoid Arthritis with Single Dose or Weekly Pulses of Chimaeric Anti-CD4 Monoclonal Antibody

The aetiology of rheumatoid arthritis is unknown but CD4+ T cells are known to be involved in its pathogenesis. Because of this, anti-CD4 monoclonal antibody has been used in open studies with clinical benefit in up to 60% of patients. We have used a chimaeric anti-CD4 monoclonal antibody (cM-T412, Centocor) in a randomized, double-blinded, placebo controlled trial as treatment for rheumatoid arthritis. Nine patients with active rheumatoid arthritis resistant to traditional disease-modifying drugs were recruited. Four received an intravenous 50 mg bolus of antibody, and three received 50 mg weekly for four consecutive weeks. Two patients received placebo. Despite a marked reduction (P less than 0.001) in peripheral blood CD4+ lymphocytes, there was no significant clinical improvement in any of these patients. The decrease in CD4+ lymphocyte number lasted one week after a single 50 mg dose of cM-T412 but was more prolonged in the patients who received four infusions. CD8+ T cells, CD16+ cytotoxic cells and CD14+ monocytes showed only a transient reduction. It may be concluded that the therapeutic efficacy of anti-CD4 therapy is not directly related to CD4+ T-cell lymphopenia.

Phenotypic expression of integrin membrane receptors on spontaneously proliferating CD8 cells in human T-lymphotropic virus type II (HTLV-II)-infected individuals

Spontaneous lymphocyte proliferation in the absence of exogenous stimulators was examined in asymptomatic HTLV-II-seropositive (n = 12) and seronegative individuals (n = 16). Mean spontaneous lymphocytic proliferation significantly increased on day 8 postculture in HTLV-II-infected individuals (5762 +/- 899 cpm) compared with normal controls (2034 +/- 925 cpm, P less than 0.01). The proliferating cells in infected individuals were predominantly T cells; neither B cells nor monocytes demonstrated any proliferation. Phenotypic analysis of cultured cells from individuals with HTLV-II infection demonstrated differential expression of integrin molecules as defined by anti-CD29 and anti-S6F1 (42.8 +/- 4.2 and 39.6 +/- 5.9%, respectively) on CD8 cells, as compared with day 0 peripheral blood mononuclear cells (PBMC) from infected individuals (19.7 +/- 3.5 and 19.9 +/- 1.9%, respectively) or normal controls (12.9 +/- 3.1 and 11.5 +/- 2.5%, respectively; P less than 0.001 for both comparisons). These CD8+ cells did not express CD16 or CD11b. The culture supernatants derived from the spontaneously proliferating cells had significantly increased levels of sCD8 and sCD25 (765 +/- 180 and 1805 +/- 320 U/ml, respectively) compared with those from normal controls (222 +/- 120 and 305 +/- 90 U/ml, respectively; P less than 0.01). Furthermore, culture supernatants derived from spontaneously proliferating PBMC from HTLV-II-infected individuals had no detectable levels of HTLV antigen and did not stimulate proliferation of PBMC from normal donors. These results suggest that the spontaneous proliferation in HTLV-II asymptomatic carriers is due to expansion of CD8 cells expressing integrin receptors which may serve as costimulatory molecules for their activation.

Comparative evaluation of fresh, fixed, and cryopreserved solid tumor cells for reliable flow cytometry of DNA and tumor associated antigen

Five different protocols for the short-term preservation of cells used for multiparameter flow cytometric assay of tumour associated antigens (TAA) and DNA were assessed in cell suspensions prepared by mechanical disaggregation of 15 gynecological tumors. The protocols at 4 degrees C were 1) storage in buffer, 2) storage in 50% methanol, and 3) storage in buffer after formalin fixation. Tissues were also cryopreserved as cell suspensions and tissue blocks. When the TAA expression and DNA histograms of the preserved cells were compared with those in fresh cell suspensions, cryopreservation was found to be the best method: TAA expression was well preserved and there was a good correlation between TAA expression and the quality of the DNA histograms, respectively, in fresh and cryopreserved cells (RS: 0.82-0.91, P less than 0.001 for all TAAs). The cell suspensions preserved at 4 degrees C all showed a significant increase in background fluorescence (P less than 0.05) and a reduction in the TAA specific fluorescence (P less than 0.011). Methanol fixation was better than buffered formalin for the proteins studied, though both gave significantly worse results than cryopreservation. The quality of these cell suspensions and the correlation with TAA measurements in fresh cell suspensions deteriorated progressively with time, particularly if they were stored more than a week.

Immunoregulation in onchocerciasis. Functional and phenotypic abnormalities of lymphocyte subsets and changes with therapy

To help define the immunoregulatory defects in patients with onchocerciasis, flow cytometric analysis of circulating lymphocyte subpopulations was performed in parallel with functional assays. No significant differences in CD4/CD8 ratios were seen when microfilariae-positive individuals from Guatemala were compared with Guatemalan controls. However, the infected individuals had significantly increased numbers of circulating CD4+CD45RA+ lymphocytes (mean 38.3%) when compared with controls (mean 16.0%). Coexpression of the activation marker HLA-DR was significantly increased on CD4+ cells from infected individuals. In contrast, no up-regulation of HLA-DR was seen on CD8+ or CD19+ cells. At 1 year after initiation of treatment with semiannual doses of the microfilaricide ivermectin, there were significant increases (P less than 0.05) in the percentage of CD4+CD45RA- cells, the percentage of CD4+HLA-DR+ cells, and mitogen-induced lymphokine production (IL-2, IL-4). Despite these changes, parasite-specific IL-2 and IL-4 production which had been undetectable before treatment did not manifest itself even by the 2-yr follow-up. Defects in the T-cell activation pathway in Onchocerca volvulus-infected individuals may thus exist at several independent points; a state of parasite antigen-specific tolerance appears to remain even after the relative reversal of other generalized immunoregulatory defects.

Flow cytometric analysis of T-lymphocyte subsets in cats

We report a rapid, reliable method for the immunophenotype analysis of feline lymphocytes. Fluorescein isothiocyanate (FITC) conjugated to murine monoclonal antibodies f43, Fel 7 and fCD8 was used to identify phenotypes corresponding to feline T-cells, CD4+ T cells and CD8+ T cells. For isolation of white blood cells, whole blood lysis was faster, less variable and required much less sample than density gradient separation. To identify feline CD4+ and CD8+ cells simultaneously, directly conjugated FITC-fCD8 and phycoerythrin (PE) fCD4 (Fel 7) were used in two-color analysis. The two T cell sub-populations were non-overlapping. Dual-label and single-label values were not significantly different. Mean lymphocyte subset percentages in conventional and specific-pathogen-free (SPF) cats did not differ significantly. These values were: pan T lymphocytes (f43), 54.8%, CD4+ cells (Fel 7), 33.9%, and CD8+ cells (fCD8), 19.1%. Mean CD4/CD8 ratio was 1.9 in normal cats; the range was 1.2-2.6.

C-reactive protein in patients with lymphatic filariasis: increased expression on lymphocytes in chronic lymphatic obstruction

Levels of C-reactive protein (CRP) were evaluated by enzyme immunoassay in patients infected with the filarial parasite Wuchereria bancrofti. Significantly elevated levels of CRP (P less than 0.001) were demonstrated in patients with chronic lymphatic pathology (CP; n = 18) compared to patients with asymptomatic microfilaremia (MF; n = 13) and normal volunteers (NV; n = 29). Serum levels of CRP showed an inverse correlation (rs = -0.37; P less than 0.05) with phosphocholine (PC)-containing filarial antigen that was present in the circulation of patients with bancroftian filariasis. Marked elevations in the percentage of CRP-binding lymphocytes were observed in patients with CP (mean = 44%; P less than 0.001) compared to those with MF (mean = 18%) or NV (mean = 3%). The increased percentage of surface CRP was not due to an abnormal change in major lymphocyte subset (CD5, CD4, CD8, or CD19). No significant correlation was noted between surface CRP and serum CRP; however, an inverse correlation was observed between surface CRP and PC-bearing circulating filarial Ag (rs = -0.64; P less than 0.001). Biosynthetic labeling and immunoprecipitation with anti-CRP antibodies indicated quantitative differences in the synthesis of CRP in patients with CP compared to MF and CP. Complexing of CRP with PC-containing Brugia malayi antigen (CRP-BmA) caused increased binding to normal lymphocytes (less than 8%), but not close to the extent seen in patients with CP (44%), suggesting de novo synthesis of CRP in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow cytometric analysis of tissue factor (TF) expression on stimulated monocytes--comparison to procoagulant activity of mononuclear blood cells

Whereas tissue factor (TF), a 47 kDa transmembrane glycoprotein, is constitutively present in certain tissues such as epithelial tissue, brain, and placenta, it is normally not expressed by cells within the vasculature. However, inflammatory mediators including bacterial lipopolysaccharide (LPS) can stimulate the expression of cell surface procoagulant activity (PCA) on monocytes. In our present study the kinetics (over 24 h) of molecular TF expression on LPS-stimulated monocytes analyzed by flow cytometry corresponds closely to functional PCA of human mononuclear blood cells (MBC). Both PCA and TF expression on monocytes were rapid events reaching their maximum after about 6 h of stimulation. At this time approximately 70-80% of monocytes had also achieved maximum anti-TF MAb receptor density. For certain analytical applications, monitoring of molecular TF expression on monocytes by flow cytometry using anti-TF MAb is favorable because there is no influence by PCA inhibitors.

Elevated levels of soluble CD8 molecule in patients with lymphatic filariasis

The serum levels of soluble forms of suppressor/cytotoxic cells (sCD8) and interleukin-2 receptor (sCD25) were analyzed in 67 patients with lymphatic filariasis and 28 normal controls. Our results show that patients with lymphatic filariasis have significantly higher levels of sCD8 (p less than 0.05) than the control groups, whereas no such difference was observed for sCD25. Within the patient group, however, those in the chronic lymphatic obstruction (CP) had significantly higher levels of both sCD8 (491 +/- 52 U/ml, p less than 0.001) and sCD25 (293 +/- 36 U/ml; p less than 0.02) than those with asymptomatic microfilaremia (sCD8 344 +/- 32 U/ml; sCD25 190 +/- 10 U/ml, respectively). No statistically significant correlation was observed between the serological levels of sCD8 and the percentage of CD8 on peripheral blood T lymphocytes in any of the patient groups. Evaluation of the activation state of B lymphocyte did not reveal any difference in the cellular expression of B7, or serum levels of soluble CD23 in any of the groups studied. Thus the selective increase of sCD8 in patients with filariasis suggests a possible pathogenic role of the cells involved in the release of this molecule.

Long-term preservation of whole blood samples for flow cytometry analysis in normal and HIV-infected individuals from Africa

A whole blood method requiring less than 4 ml of heparinized blood was developed to assess the practicality of preparing whole blood samples that could be easily stored, transported and readily used to determine the lymphocyte phenotypes and proliferation responses of individuals from remote areas who are infected with the human immunodeficiency virus. Minor modifications in standard whole blood procedure for lymphocyte phenotyping have significantly increased the stability of light scatter and fluorescence intensity of the cells for subsequent flow cytometry (FC) analysis. These changes include removal of lysis solution prior to fixation, fixation of monoclonal antibody-stained cells in 1% paraformaldehyde for 30 minutes and storage of fixed samples in medium containing 1% bovine serum albumin. Lymphocyte subsets and their functional subsets could reliably be determined on samples stored for up to 4 weeks. Further, blood samples could be kept at room temperature for up to 96 hours or at ambient temperature during transportation from Africa before staining for FC without affecting their quantitation. While samples could be processed for FC analysis under field-laboratory conditions, proliferation assays could only be performed on samples that were transported within 48 hours of their collection. The whole blood method saves time and expense and decreases the volumes of blood required to perform phenotypic analysis and functional assays on specimens collected in remote areas.