Flow cytometric detection of cytomegalovirus antigen in peripheral blood cells after bone marrow transplantation

We report 13 normal peripheral blood stem cell (PBSC) donors who had a second PBSC collection for allogeneic transplantation performed after the first. The median interval between the first and second collection was 5 months. Mobilization was achieved with filgrastim (12 μg/kg/d). No significant difference was found in the median pre-apheresis leucocyte count (×10⁹/l) between the two donations (40.2 v 38.5; P  = 0.91). The median apheresis yield (×10⁶ CD34⁺ cells/litre blood processed, first apheresis) was also similar (28 v 27.3; P  = 0.91). Filgrastim-related adverse events were comparable. These data suggest that second PBSC collections are feasible, similarly tolerated and provide comparable apheresis yields.     

Flow cytometric measurement of DNA S-phase in human bone marrow cells: correcting for peripheral blood contamination

Abstract: The relationship between bone marrow (BM) cells with S-phase DNA content and the amount of peripheral blood contamination estimated as percentage lymphocytes+monocytes (L+MO) present in BM samples has been investigated in a total of 136 BM aspirates and biopsy expellates from 35 hematologically healthy individuals. A significant negative correlation was demonstrated between total, erythroid and myeloid BM cells in S-phase and the percentage of L+MO in the aspirates (r = 0.84, 0.57 and 0.49, respectively; p<0.0001). Based on the equation of the slope of the regression line, a correction formula adjusting the measured value of BM cells in S-phase to varying amounts of L+MO percentage has been worked out for the total and erythroid BM cells. In contrast, highly proliferating myelomonocytic cells and CD34⁺ cells did not show any significant correlation between cells in S-phase and percentage L+MO, indicating that peripheral blood contamination of BM aspirates is not a problem regarding kinetic investigations of these cells. In conclusion, the described flow cytometric method of analysing BM aspirates estimates the degree of peripheral blood contamination, as well as make possible a correct estimation of the DNA synthesis of several BM populations. The method is especially applicable when frequent BM sampling is required.     

Flow cytometric assessment of human MIC2 expression in bone marrow, thymus, and peripheral blood

The cell-surface expression of the MIC2 antigen defined by the monoclonal antibody 12E7 was investigated on human leukocytes in bone marrow (BM), thymus, and peripheral blood (PB) using multiparameter flow cytometry and cell sorting. In contrast to preceding reports, we found that the MIC2 antigen is not restricted to T cells and monocytes. We show that it is also expressed in the B cell and in the granulocytic lineage, the levels of expression being related to distinct maturational stages. CD34+ cells of BM were found to express the antigen at high levels. Along the granulocytic maturation pathway from CD34+CD33+ blasts to mature granulocytes, MIC2 densities appeared progressively reduced with a considerable decline at the myelocyte stage. In B lymphopoiesis, the earliest CD34+ CD10+ B-cell precursor (BCP) cells, further subdivided by expression of CD19, displayed the highest MIC2 density of BM leukocytes. All later BCP stages showed lower MIC2 expression levels, with a remarkable reduction concomitant with loss of the CD34 antigen at the CD10+CD20- surface mu-chain- stage, and a subsequent slight upregulation along with maturation to CD10-CD20high surface mu-chain+ BCPs. The brightest MIC2 expression of all cells tested was displayed by the most immature thymic T-lineage cells characterized by the antigenic profile CD34weakor- CD7++ surface CD3-CD1a(weak) CD4weak CD8-or weak. Common thymocytes stained slightly less intense with 12E7, whereas all subsequent stages of T-lineage cells in thymus, PB, or BM showed markedly reduced MIC2 levels. Mature peripheral CD4+ as well as CD8+ T cells displayed a bimodal distribution of MIC2. In the CD4+ population, the distinct MIC2 levels were related to the well-studied functional subdivision by differential expression of CD45 isoforms, the helper-inducer/memory subset showing higher MIC2 expression than helper-suppressor/naive CD4+ T cells. Similarly high MIC2 densities were found on CD16+ natural killer cells and on CD14+ monocytes, whereas mature peripheral B cells exhibited low or intermediate expression, and granulocytes exhibited no or only dim expression. These results document that the MIC2 antigen (1) is expressed on all leukocyte lineages; (2) is differentially expressed during T- and B-lymphoid, as well as granulocytic maturation; (3) shows highest expression in the most immature lymphocytic and granulocytic developmental stages; and (4) is also differentially expressed on functional T-cell subsets. We speculate that these observations imply a functional significance of MIC2 in the network of hematopoietic adhesion pathways.     

Flow cytometric analysis of dengue virus-infected cells in peripheral blood

With the development of permeabilization techniques in flow cytometry and the availability of various monoclonal antibodies (MAbs) that specifically bind with cell surface and intracellular antigens, it is now possible to use flow cytometric assay to identify dengue virus (DEN) infected cells in peripheral blood. Blood samples were analyzed using phycoerythrin (PE) labeled anti-CD3, anti-CD14, anti-CD16, and anti-CD19 antibodies and Alexa Fluor 488 labeled anti-flavivirus monoclonal antibody (MAb) 6B6C-1. The predominant DEN-infected cells were CD19+ in this study. There was dim partial to moderately bright partial expression of CD19 positive cells in the blood samples tested. Virus isolation and serotype-specific RT-PCR revealed the cells were infected with dengue serotype 3 (DEN3). Our results suggest B cells may play an important role in DEN1 and DEN3 replication, and dissemination in vivo.     

Highly increased production of bone marrow-derived blood cells by administration of homologous interleukin-3 to rhesus monkeys

Recombinant rhesus monkey interleukin-3 (IL-3) was administered to normal rhesus monkeys in graded doses ranging from 3 to 30 micrograms/kg/d subcutaneously for 30 consecutive days or given as a continuous intravenous infusion at a dose of 30 micrograms/kg/d for 16 days. After a lag phase of about 1 week, a highly increased, dose-dependent production of bone marrow-derived blood cells was observed, preceded by amplification of bone marrow hematopoietic progenitor cells. Simultaneously, peripheral blood progenitor cells rose. The increase included basophilic, eosinophilic and neutrophilic granulocytes, monocytes, and the erythrocyte and platelet lineages. Characteristically, a T-lymphocyte response was absent. It is concluded that IL-3 in vivo stimulates blood cell production from an immature, multipotent progenitor cell.     

Immunomagnetic depletion of CD6+ cells from bone marrow and peripheral blood

Depletion of donor CD6+ cells in HLA-identical allogeneic bone marrow transplantation has been reported to reduce graft-versus-host disease without interfering with engraftment. We have established an immunomagnetic cell separation technique capable of producing a 2-3 log depletion of CD6+ cells. Median recovery of CD6- cells and hematopoietic progenitor cells was 65-70%, and cell viability was unaffected. Significant numbers of CD2+, CD3+ cells responsive to phytohemagglutinin (PHA), OKT3, recombinant interleukin-2 (rIL-2), and allogeneic cells remained after depletion, and the number of cells able to respond to stimulation with PHA and IL-2 in vitro was reduced by only 1-2 log. These observations are not easily reconciled with the ability of CD6 depletion to prevent GVHD, but raise the question whether the depletion causes a sufficient reduction of the T cell load or removes a critical T cell subset.     

Flow cytometric immunophenotyping is of great value to diagnosis of natural killer cell neoplasms involving bone marrow and peripheral blood

Natural killer (NK) cell neoplasms are unusual disorders. In this study we compared results of flow cytometric immunophenotype (FCI) with cytomorphology, histopathology and clinical findings in a series of patients with NK cell neoplasms with peripheral blood and/or bone marrow involvement, and the FCI of neoplastic and normal NK cells were compared. Retrospective data and specimens (bone marrow aspiration or peripheral blood) from 71 cases of NK cell neoplasms were obtained. All patients have been demonstrated laboratory and clinical features consistent with NK cell neoplasms, and the subtypes were determined by integrated clinical estimation. Routine 4-color flow cytometry (FCM) using a NK/T cell related antibody panels was performed. NK cell neoplasms were divided into two major subtypes by FCI, namely malignant NK cell lymphoma, including extranodal nasal type NK cell lymphoma (ENKL, 11 cases) and aggressive NK cell lymphoma/leukemia (ANKL, 43 cases), and relative indolent chronic lymphoproliferative disorder of NK cell (CLPD-NK, 17 cases). The former exhibited stronger CD56-expressing, larger forward scatter (FSC) and more usually CD7- and CD16-missing. FCI of CLPD-NK was similar to normal NK cells, but CD56-expressing was abnormal, which was negative in five cases and partially or dimly expressed in eight cases. Cytomorphologic abnormal cells were found on bone marrow slides of 4 cases of ENKL and 30 cases of ANKL. Eight cases of ENKL were positive in bone marrow biopsies, and other three cases were negative. In 32 cases of ANKL which bone marrow biopsies were applied, 21 cases were positive in the first biopsies. Lymphocytosis was found only in six cases of CLPD-NK by cytomorphology, and biopsy pathology was not much useful for diagnosing CLPD-NK. These results suggest that FCM analysis of bone marrow and peripheral blood was superior to cytomorphology, bone marrow biopsy, and immunohistochemistry in sensitivity and early diagnosis for ANKL, stage III/IV ENKL and CLPD-NK. FCI could not only define abnormal NK cells but also determine the malignant classification. It is beneficial for clinical management and further study of NK cell neoplasms.     

Differential expression of receptors for interleukin-3 on subsets of CD34-expressing hematopoietic cells of rhesus monkeys

The target cell specificity of interleukin-3 (IL-3) was examined by flow cytometric analysis of IL-3 receptor (IL-3R) expression on rhesus monkey bone marrow (BM) cells using biotinylated IL-3. Only 2% to 5% of unfractionated cells stained specifically with the biotinylated IL-3 and most of these cells were present within the CD34+ subset. IL-3Rs were detected on small CD34dull/RhLA-DRbright/CD10+/CD27+/CD2-/++ +CD20- cells, which probably represent B-cell precursors. IL-3R+ CD34- BM cells, which were detected at low frequencies, consisted of small CD20dull/surface-IgM+/RhLA-DR+ cells. These cells represented immature B lymphocytes, whereas CD20bright mature B cells were IL-3R-. The highest IL-3R levels were detected on CD34dull/RhLA-DRbright blast-like cells. These cells differentiated into monocytes, neutrophils, and basophils after IL-3 and/or granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulation in vitro. The CD34bright/IL-3R- subset contained all clonogenic erythroid and myeloid progenitors (burst- forming unit-erythroid and colony-forming unit-culture), whereas CD34bright/IL-3Rdull cells differentiated into monocytes, neutrophils, and erythroid cells after shorter culture periods. This finding showed that IL-3R expression increases during monocyte and granulocyte differentiation. Results of three-color experiments indicated that IL- 3Rs are expressed on CD34bright/RhLA-DRbright cells as well as on CD34bright/RhLA-DRdull cells, with the latter population expression approximately twofold to threefold lower IL-3R levels. A large fraction (> 30%) of single-cell/well-sorted CD34bright/RhLA-DRdull cells formed multilineage colonies after 2 to 4 weeks of stimulation with IL-3, GM- CSF, Kit ligand, and IL-6. Individual colonies contained cells that still expressed CD34 as well as differentiated monocytes, granulocytes, and erythroid cells. These results confirmed that the CD34bright/RhLA- DRdull subset was enriched for immature, multipotent progenitor cells, whereas the CD34bright/RhLA-DRbright population mainly contained lineage-committed precursors. The results are consistent with the concept that IL-3Rs are induced at very early stages of hematopoiesis, as identified by high expression of CD34 and low expression of RhLA-DR. IL-3R expression continues to be low during differentiation into lineage-committed progenitors; gradually increases on differentiating progenitor cells for B cells, granulocytes, monocytes, and, possibly also, erythrocytes; but finally declines to undetectable levels during terminal differentiation into mature cells of all lineages in peripheral blood, with the exception of basophils.(ABSTRACT TRUNCATED AT 400 WORDS)     

Flow cytometric DNA quantification in immunophenotyped cells as a sensitive method for determination of aneuploid multiple myeloma cells in peripheral blood stem cell harvests and bone marrow after therapy.

The simultaneous measurement of DNA content and myeloma-related antigens (B-B4 or CD38) by flow cytometry is proposed as a method for the detection of aneuploid plasma cells in peripheral blood stem cell (PBSC) harvests and in bone marrow after therapy. In 30 patients with initially detected aneuploid myeloma cells we evaluated the bone marrow after therapy and in eight of these patients 23 PBSC harvests were analyzed. In 13 of 23 PBSC harvests aneuploid myeloma cells were detectable (range: 0.02-0.63%). In the bone marrow of the 30 patients aneuploid plasma cells were detectable in all samples after chemotherapy (range: 0.12-35.70%) and after autologous PBSC transplantation in two of three patients (0.21% and 0.03%). Furthermore the relationship between diploid and aneuploid plasma cells can be evaluated. In the PBSC harvests the percentage of aneuploid plasma cells is significantly lower than that of diploid plasma cells (P=0.006). In contrast, in bone marrow the aneuploid plasma cells are predominant in most patients even after therapy (24 of 30 patients; P=0.0055). In the case of initially detected aneuploid myeloma cells, a contamination with malignant cells can be estimated with a simple flow cytometric method in PBSC harvests and in bone marrow after therapy.     

Flow cytometric analysis of defensins in blood and marrow neutrophils

Polymorphonuclear neutrophils (PMN) are vital in host defense against microbial infections. This study provides a flow cytometric method for the quantitative analysis of microbicidal peptides (defensins) in cells of PMN lineage. Rabbit neutrophil peptides, NP-2 and NP-5, were measured in all PMN and in subpopulations of PMN expressing 1-selectin. PMN lineage counts were made on Wright's-stained blood smears and marrow cytospins. Immunoreactivity for NP-2, and NP-5 was detected by using the alkaline phosphatase anti-alkaline phosphatase technique. The results show that marrow PMN express higher levels of NP-2 and NP-5 than blood PMN, p < 0.001 and that these levels are associated with elevated numbers of myeloid precursors. In both blood and marrow, NP-2 occurs in two PMN subpopulations and the mean fluorescence intensity of NP-2 is consistently higher than that of NP-5. Increased levels of defensins are observed in circulating PMN depicting the most 1-selectin p < 0.05. Immunocytochemical results indicate that PMN defensins reside in cytoplasmic granules and are not constitutively expressed on the cell surface. Furthermore, defensins are not detected in monocytes, eosinophils, lymphocytes and erythrocytes. The flow cytometric method described here provides a novel means of quantitating host natural defenses, allows the characterization of PMN subpopulations and has clinical applications.     

Flow cytometric detection of CD10 (cALLA) on peripheral blood B lymphocytes of neonates

CD10 (cALLA) was detected on the surface of CD19-positive circulating lymphocytes in the peripheral blood of 32/50 neonates tested. These cells are presumed to represent immature B cells, commonly referred to as haematogones, previously undescribed in peripheral blood. The CD10+/CD19+ cells expressed lower levels of CD22 consistent with these cells being immature B lymphocytes. The presence of CD10+/CD19+ cells in the blood was not significantly correlated with a leucoerythroblastic picture, adjusted gestational age, or the presence in blood smears of medium-to-large lymphocytes with an immature appearance that morphologically resembled classic bone-marrow haematogones.     

Hemodialysis-related induction of interleukin-6 and interleukin-8 production by peripheral blood mononuclear cells

ObjectiveTo investigate whether interleukin-6 (IL-6) and interleukin-8 (IL-8) can be used as the evaluating indices of dialyzer biocompatibility.MethodsThe levels of plasma IL-6 and IL-8 were measured by the sandwich enzyme linked immunosorbent assay (ELISA) method in 15 hemodialysis (HD) patients with end-stage renal failure (ESRF) before and post HD. Those patients were randomly divided into three groups according to the dialysis membrane used: cellulose acetate (CA) membrane group, Hemophan (HE) membrane group and polysulfone (Psu) membrane group respectively. Another five non-HD (NHD) ESRF patients and five healthy subjects were selected as controls.ResultsThe plasma of IL-6 and IL-8 levels in the CA and HE groups were significantly higher than that of patients in the Psu group, NHD patients and normal subjects (p < 0.05). Moreover, no significant difference could be demonstrated in the plasma IL-6 and IL-8 concentrations between patients in the CA and HE groups (p > 0.05), and among patients in the Psu group, NHD patients and normal subjects (p > 0.05). There was also no difference in the levels of IL-6 and IL-8 in patients dialyzed with the three different dialyzers between pre- and post-dialysis. However, a significant positive linear correlation existed between the plasma IL-6 and IL-8 levels (p < 0.05).ConclusionOur results suggest that the levels of plasma IL-6 and IL-8 were related to the type of dialyzers and could be used as indices evaluating the biocompatibility of dialyzers. Furthermore, the change of one cytokine can indirectly reflect the tendency of the other.     

Differentiation of early plasma cells on bone marrow stromal cells requires interleukin-6 for escaping from apoptosis

The bone marrow (BM) is well known to be the major site of Ig production in secondary immune responses; thus, the microenvironment of BM is considered to be essential for final differentiation of plasma cells. We identified in the peripheral blood (PB) early plasma cells (CD38++CD19+VLA-5-) committed to entering the BM. The sorted early plasma cells rapidly entered apoptosis in vitro, but these cells could survive and further differentiate into mature plasma cells (CD38 CD19+) just as BM plasma cells in the presence of a BM-derived stromal cell line (KM-102). Culture supernatants of KM-102 cell lines could also support survival of these cells, and antibody to interleukin-6 (IL-6) completely blocked the effect of these supernatants. Furthermore, recombinant IL-6, but not IL-1 or IL-3, could support their survival and their differentiation into mature plasma cells (CD38 CD19+VLA-5+) with expression of VLA-5 mRNA. Therefore, here is direct evidence that early plasma cells found in the PB differentiated into mature plasma cells with stromal cell-derived IL-6 in vitro; thus, BM stromal cells control the final checkpoint of plasma cell differentiation with secretion of IL-6 in the BM.     

Usefulness of flow cytometric detection of cell surface interleukin-6 receptors in human myeloma cell lines

A flow cytometric procedure was used to analyse the cell surface interleukin-6 receptor (IL-6R) based on the principle of detecting the binding of IL-6 to IL-6R. The bound IL-6 was visualized by reacting with anti-IL-6 antibody, a second biotinylated antibody to immuno globulins, fluorescein-conjugated avidin and biotinylated, fluorescein-conjugated bovine serum albumin. Studies with a number of human myeloma cell lines showed that the fluorescence signal from cellular binding of IL-6, and thus IL-6R, could be specifically discerned from the background. The specific IL-6R signal could be semi-quantitatively expressed as the mean channel number of the fluorescence histogram or as relative IL-6R density in relation to a reference cell line, such as U266-BL cells. The relative IL-6R density of various myeloma cell lines thus determined was found to correlate with their sensitivity to the growth inhibitory effect of glucocorticoids in vitro. Quantitatively, calibration of the staining procedure with microbeads that have a defined binding capacity for anti-IL-6 antibody allowed calculation of cellular IL-6R density that yielded results close to that reported with conventional radio-ligand binding assay. Similarly, the cytometric method was applied to the studies of kinetics of IL-6/IL-6R interaction and the cellular IL-6R changes after ligand-binding to provide estimates of IL-6R binding affinity and IL-6R turnover rate. It is suggested that flow cytometric measurement of cellular IL-6R is useful in providing biologically relevant information on myeloma cells.     

Recombinant glycosylated human interleukin-6 accelerates peripheral blood platelet count recovery in radiation-induced bone marrow depression in baboons.

This report was aimed at confirming the potential clinical use for a genetically engineered glycosylated human interleukin-6 (rhIL-6) in hematopoiesis. Its tolerance and efficacy were assessed on hematopoietic restoration after neutron radiation-induced bone marrow injury on baboons, which represent an adequate model of parallelism for studying hematology in the human. The particular neutron radiation absorption pattern in the body allows the preservation of underexposed bone marrow areas that mimics an autotransplantation-like situation. An initial dose finding study (1 microgram up to 20 micrograms/kg/d for 8 consecutive days) in normal baboons established a dose-dependent response regarding the peripheral platelet count (range of increase, 1.5- to 4-fold). A significant elevation in white blood cell (WBC) count, as well as a substantial reversible normochromic normocytic anemia, were observed for the highest doses only (10 and 20 micrograms/kg/d). All rhIL-6 administered doses were clinically well tolerated. In myelosuppressed baboons, a selected dose of 10 micrograms/kg/d of rhIL-6 for 13 consecutive days significantly lessened the degree of induced thrombocytopenia as compared with the control group (P = .01) and shortened the time to occurrence of the nadir, showing that the onset of recovery occurs much earlier, ie, an average of 5 days (P = .003), in the treated group. Moreover, this accelerated platelet recovery is evidenced by an 8-day shorter mean time back to baseline values (P = .03) in the rhIL-6--treated animals. At this dose no effect was observed on the WBC recovery pattern. Importantly rhIL-6 did not accentuate the radiation-induced anemia and was clinically well tolerated. All tested monkeys recovered from their induced pancytopenia and no animal loss was recorded. IL-6, tumor necrosis factor, and IL-1 blood measurements are reported. In conclusion, rhIL-6 is a potent thrombopoietic factor for the treatment of induced thrombocytopenia in nonhuman primates at a clinically well-tolerated dose.     

Proliferation and cytolytic function of anti-CD3 + interleukin-2 stimulated peripheral blood mononuclear cells following bone marrow transplantation.

We evaluated the proliferation, cytolytic function, and phenotypic characteristics of anti-CD3 plus interleukin-2 (IL-2) stimulated peripheral blood mononuclear cells (PBMCs) from 44 patients with leukemia or non-Hodgkin's lymphoma (NHL) treated with multiagent chemotherapy or following bone marrow transplantation (BMT). BMT patients had decreased cell growth with only a 1.35 +/- 0.25 (autologous BMT for acute lymphoblastic leukemia [ALL]), 1.24 +/- 0.25 (autologous BMT for NHL), and 0.8 +/- 0.1 (allogeneic BMT for leukemia) mean fold increase by day 5 of culture compared with controls (4.0 +/- 0.4), P less than .001. Anti-CD3 + IL-2 activated cells from patients with ALL and NHL who had received autologous BMT and cells from patients with leukemia who underwent allogeneic BMT were more effective in lysing the natural killer (NK) sensitive target, K562, and the NK-resistant target, Daudi, compared with controls. In contrast, cytolysis of K562 and Daudi by cultured PBMCs from patients with ALL and NHL receiving multi-agent chemotherapy was similar to that of controls. Cultures from BMT recipients had a significant increase in CD16+ (autologous ALL 5.7 +/- 1.5%, P less than .01; autologous NHL 12.4 +/- 3.5%, P less than .001; allogeneic 14.3 +/- 2.9%, P less than .001) and CD56+ cells (autologous ALL 27.6 +/- 12.0%, P less than .01; autologous NHL 39.3 +/- 9.5%, P less than .001; allogeneic 42.7 +/- 7.4%, P less than .001) compared with controls (CD16+ 2.5 +/- 0.4%; CD56+ 6.9 +/- 0.9%). Stimulation of PBMCs with anti-CD3 + IL-2 is effective in generating cells with high cytolytic function post-BMT.     

Flow cytometric detection of hepatitis C virus antigens in infected peripheral blood leukocytes： Binding and entry

AIM: We designed two synthetic-core-specific peptides core 1 (C1) and core 2 (C2), and an El-specific peptide (El). We produced specific polyclonal antibodies against these peptides and used the antibodies for detection of HCV antigens on surface and within infected peripheral blood leukocytes. METHODS: Peripheral blood from a healthy individual who tested negative for HCV RNA was incubated with HCV type 4 infected serum for 1 h and 24 h at 37 ℃. Cells were stained by direct and indirect immunofluorescence and measured by flow cytometry. RESULTS: After 1 h of incubation, antibodies against C1, C2, and E1 detected HCV antigens on the surface of 27%, 26% and 73% of monocytes respectively, while 10%, 5% and 9% of lymphocytes were positive with anti-C1, anti-C2 and anti-E1 respectively. Only 1-3% of granulocytes showed positive staining with anti-C1, anti-C2 and anti E1 antibodies. After 24 h of incubation, we found no surface staining with anti-C1, anti-C2 or anti-E1. Direct immunostaining using anti-C2 could not detect intracellular HCV antigens, after 1 h of incubation with the virus, while after 24 h of incubation, 28% of infected cells showed positive staining. Only plus strand RNA was detectable intracellularly as early as 1 h after incubation, and remained detectable throughout 48 h post-infection. Interestingly, minus RNA strand could not be detected after 1 h, but became strongly detectable intracellularly after 24 h post-infection. CONCLUSION: Monocytes and lymphocytes are the preferred target cells for HCV infection in peripheral blood leukocytes. Our specific anti-core and anti-El antibodies are valuable reagents for demonstration of HCV cell cycle. Also, HCV is capable of infecting and replicating in peripheral blood mononuclear cells as confirmed by detection of minus strand HCV RNA as well as intracellular staining of core HCV antigen.