CD45 (leucocyte common antigen) expression in T and B lymphocyte subsets

Multiresolution 3D Optical Mapping of Immune Cell Infiltrates in Mouse Asthmatic Lung

Asthma is a chronic inflammatory airway disease driven by various infiltrating immune cell types into the lung. Optical microscopy has been used to study immune infiltrates in asthmatic lungs. Confocal laser scanning microscopy (CLSM) identifies the phenotypes and locations of individual immune cells in lung tissue sections by employing high-magnification objectives and multiplex immunofluorescence staining. In contrast, light-sheet fluorescence microscopy (LSFM) can visualize the macroscopic and mesoscopic architecture of whole-mount lung tissues in three dimensions (3D) by adopting an optical tissue-clearing method. Despite each microscopy method producing image data with unique resolution from a tissue sample, CLSM and LSFM have not been applied together because of different tissue-preparation procedures. Here, we introduce a new approach combining LSFM and CLSM into a sequential imaging pipeline. We built a new optical tissue clearing workflow in which the immersion clearing agent can be switched from an organic solvent to an aqueous sugar solution for sequential 3D LSFM and CLSM of mouse lungs. This sequential combination microscopy offered quantitative 3D spatial analyses of the distribution of immune infiltrates in the same mouse asthmatic lung tissue at the organ, tissue, and cell levels. These results show that our method facilitates multiresolution 3D fluorescence microscopy as a new imaging approach providing comprehensive spatial information for a better understanding of inflammatory lung diseases.

The Mechanisms of Zinc Action as a Potent Anti-Viral Agent: The Clinical Therapeutic Implication in COVID-19

The pandemic of COVID-19 was caused by a novel coronavirus termed as SARS-CoV2 and is still ongoing with high morbidity and mortality rates in the whole world. The pathogenesis of COVID-19 is highly linked with over-active immune and inflammatory responses, leading to activated cytokine storm, which contribute to ARDS with worsen outcome. Currently, there is no effective therapeutic drug for the treatment of COVID-19. Zinc is known to act as an immune modulator, which plays an important role in immune defense system. Recently, zinc has been widely considered as an anti-inflammatory and anti-oxidant agent. Accumulating numbers of studies have revealed that zinc plays an important role in antiviral immunity in several viral infections. Several early clinical trials clearly indicate that zinc treatment remarkably decreased the severity of the upper respiratory infection of rhinovirus in humans. Currently, zinc has been used for the therapeutic intervention of COVID-19 in many different clinical trials. Several clinical studies reveal that zinc treatment using a combination of HCQ and zinc pronouncedly reduced symptom score and the rates of hospital admission and mortality in COVID-19 patients. These data support that zinc might act as an anti-viral agent in the addition to its anti-inflammatory and anti-oxidant properties for the adjuvant therapeutic intervention of COVID-19.

T cell markers recount the course of immunosenescence in healthy individuals and chronic kidney disease

Aging results in substantial changes in almost all cellular subpopulations within the immune system, including functional and phenotypic alterations. T lymphocytes, as the main representative population of cellular immunity, have been extensively studied in terms of modifications and adjustments during aging. Phenotypic alterations are attributed to three main mechanisms; a reduction of naïve T cell population with a shift to more differentiated forms, a subsequent oligoclonal expansion of naïve T cells characterized by repertoire restriction, and replicative insufficiency after repetitive activation. These changes and the subsequent phenotypic disorders are comprised in the term "immunosenescence". Similar changes seem to occur in chronic kidney disease, with T cells of young patients resembling those of healthy older individuals. A broad range of surface markers can be utilized to identify immunosenescent T cells. In this review, we will discuss the most important senescence markers and their potential connection with impaired renal function.

KCTD15 Protein Expression in Peripheral Blood and Acute Myeloid Leukemia

Leukocytes are major cellular components of the inflammatory and immune response systems. After their generation in the bone marrow from hematopoietic stem cells, they maturate as granulocytes (neutrophils, eosinophils, and basophils), monocytes, and lymphocytes. The abnormal accumulation and proliferation of immature blood cells (blasts) lead to severe and widespread diseases such as leukemia. We have recently shown that KCTD15, a member of the potassium channel tetramerization domain containing protein family (KCTD), is remarkably upregulated in leukemic B-cells. Here, we extend our investigation by monitoring the KCTD15 expression levels in circulating lymphocytes, monocytes, and granulocytes, as well as in leukemia cells. Significant differences in the expression level of KCTD15 were detected in normal lymphocytes, monocytes, and granulocytes. Interestingly, we also found overexpression of the protein following leukemic transformation in the case of myeloid cell lineage. Indeed, KCTD15 was found to be upregulated in K562 and NB4 cells, as well as in HL-60 cell lines. This in vitro finding was corroborated by the analysis of KCTD15 mRNA of acute myeloid leukemia (AML) patients reported in the Microarray Innovations in Leukemia (MILE) dataset. Collectively, the present data open interesting perspectives for understanding the maturation process of leukocytes and for the diagnosis/therapy of acute leukemias.

Identification of human endogenous retrovirus transcripts in Hodgkin Lymphoma cells

During the last decades, the prognosis for patients with Hodgkin Lymphoma (HL) has been steadily improved. Nevertheless, new and less toxic therapy strategies have to be developed especially for patients with advanced disease. The activation of human endogenous retroviruses (HERV) is suspected to occur in HL and therefore, HERV might represent interesting target structures. In order to identify transcribed HERV of the HERV-H and HERV-K families in HL we used a reverse transcription-polymerase chain reaction based cloning approach. In addition to unspliced HERV-H and HERV-K transcripts, we detected spliced HERV-K transcripts that matched genomic sequences with the expected splicing-donor and splicing-acceptor sites. Of particular interest was the expression of HERV-K18 related transcripts at the CD48 locus. Our data indicate transcriptional activity of several HERV loci in HL cells.

Immunophenotypic profile of leukocytes in hyperandrogenemic female rat an animal model of polycystic ovary syndrome

The immune etiology of polycystic ovary syndrome (PCOS) is an intriguing area. However, whether there is alteration in the leukocyte populations in different tissues remain ambiguous.

AIM

To characterize the leukocyte populations of hyperandrogenemic female (HAF) rat tissues.

METHODS

Female Sprague Dawley rats at 3 weeks of age were implanted subcutaneously with dihydrotestosterone (DHT) or placebo pellets. The rats were aged to 14-15 weeks and tissues were collected.

RESULTS

Peripheral blood (PB) and renal CD4⁺ (P < 0.03, P < 0.007), Th17 (P < 0.05, P < 0.002), and CD4⁺CD28^null (P < 0.04, P < 0.001) were significantly increased in HAF rats compared to placebo, respectively, in spite of their lower percentage in the spleen. Although, the percentage of Treg T lymphocytes were significantly higher in the PB (P < 0.001) of HAF rats, the splenic (P < 0.01) and renal Treg cells (P < 0.03) were found to be significantly lower. Remarkably, HAF rats had higher renal mast cells (P < 0.00009) despite lower splenic (P < 0.002). The number of PB, renal, and splenic CD8⁺ T cells and IgM⁺-B cells in HAF rats remained unchanged.

CONCLUSION

Results from this study 1) provide the first evidence of significant alteration of T lymphocyte subsets and different leukocyte populations profile in a rat model of polycystic ovary syndrome, 2) demonstrate alteration of the immunological niche of blood, spleen, and kidney tissues in Hyperandrogenemia state in female rats, 3) imply potential immune system dysregulation in HAF rats which may suggest a link between excess androgen, chronic inflammation, and immune-mediated diseases in polycystic ovary syndrome patients.

CD45 in human physiology and clinical medicine

CD45 is an evolutionary highly conserved receptor protein tyrosine phosphatase exclusively expressed on all nucleated cells of the hematopoietic system. It is characterized by the expression of several isoforms, specific to a certain cell type and the developmental or activation status of the cell. CD45 is one of the key players in the initiation of T cell receptor signaling by controlling the activation of the Src family protein-tyrosine kinases Lck and Fyn. CD45 deficiency results in T- and B-lymphocyte dysfunction in the form of severe combined immune deficiency. It also plays a significant role in autoimmune diseases and cancer as well as in infectious diseases including fungal infections. The knowledge collected on CD45 biology is rather vast, but it remains unclear whether all findings in rodent immune cells also apply to human CD45. This review focuses on human CD45 expression and function and provides an overview on its ligands and role in human pathology.

Skeletal stem cell isolation: A review on the state-of-the-art microfluidic label-free sorting techniques

Skeletal stem cells (SSC) are a sub-population of bone marrow stromal cells that reside in postnatal bone marrow with osteogenic, chondrogenic and adipogenic differentiation potential. SSCs reside only in the bone marrow and have organisational and regulatory functions in the bone marrow microenvironment and give rise to the haematopoiesis-supportive stroma. Their differentiation capacity is restricted to skeletal lineages and therefore the term SSC should be clearly distinguished from mesenchymal stem cells which are reported to exist in extra-skeletal tissues and, critically, do not contribute to skeletal development. SSCs are responsible for the unique regeneration capacity of bone and offer unlimited potential for application in bone regenerative therapies. A current unmet challenge is the isolation of homogeneous populations of SSCs, in vitro, with homogeneous regeneration and differentiation capacities. Challenges that limit SSC isolation include a) the scarcity of SSCs in bone marrow aspirates, estimated at between 1 in 10-100,000 mononuclear cells; b) the absence of specific markers and thus the phenotypic ambiguity of the SSC and c) the complexity of bone marrow tissue. Microfluidics provides innovative approaches for cell separation based on bio-physical features of single cells. Here we review the physical principles underlying label-free microfluidic sorting techniques and review their capacity for stem cell selection/sorting from complex (heterogeneous) samples.

What makes cancer stem cell markers different?

Since the cancer stem cell concept has been widely accepted, several strategies have been proposed to attack cancer stem cells (CSC). Accordingly, stem cell markers are now preferred therapeutic targets. However, the problem of tumor specificity has not disappeared but shifted to another question: how can cancer stem cells be distinguished from normal stem cells, or more specifically, how do CSC markers differ from normal stem cell markers? A hypothesis is proposed which might help to solve this problem in at least a subgroup of stem cell markers. Glycosylation may provide the key.

The immunological contribution of NF-κB within the tumor microenvironment: a potential protective role of zinc as an anti-tumor agent

Over decades, cancer treatment has been mainly focused on targeting cancer cells and not much attention to host tumor microenvironment. Recent advances suggest that the tumor microenvironment requires in-depth investigation for understanding the interactions between tumor cell biology and immunobiology in order to optimize therapeutic approaches. Tumor microenvironment consists of cancer cells and tumor associated reactive fibroblasts, infiltrating non-cancer cells, secreted soluble factors or molecules, and non-cellular support materials. Tumor associated host immune cells such as Th(1), Th(2), Th17, regulatory cells, dendritic cells, macrophages, and myeloid-derived suppressor cells are major components of the tumor microenvironment. Accumulating evidence suggests that these tumor associated immune cells may play important roles in cancer development and progression. However, the exact functions of these cells in the tumor microenvironment are poorly understood. In the tumor microenvironment, NF-κB plays an important role in cancer development and progression because this is a major transcription factor which regulates immune functions within the tumor microenvironment. In this review, we will focus our discussion on the immunological contribution of NF-κB in tumor associated host immune cells within the tumor microenvironment. We will also discuss the potential protective role of zinc, a well-known immune response mediator, in the regulation of these immune cells and cancer cells in the tumor microenvironment especially because zinc could be useful for conditioning the tumor microenvironment toward innovative cancer therapy.

Molecular Pathogenesis of Hodgkin's Lymphoma: Increasing Evidence of the Importance of the Microenvironment

Hodgkin's lymphoma (HL) represents the most common subtype of malignant lymphoma in young people in the Western world. Most patients can be cured with modern treatment strategies, although approximately 20% will die after relapse or progressive disease. The histologic hallmark of the disease is the presence of the characteristic Hodgkin Reed-Sternberg (HRS) cells in classical HL and so-called lymphocyte-predominant (LP) cells in nodular lymphocyte-predominant HL. HL is unique among all cancers because malignant cells are greatly outnumbered by reactive cells in the tumor microenvironment and make up only approximately 1% of the tumor. Expression of a variety of cytokines and chemokines by the HRS and LP cells is believed to be the driving force for an abnormal immune response, perpetuated by additional factors secreted by reactive cells in the microenvironment that help maintain the inflammatory milieu. The malignant HRS and LP cells manipulate the microenvironment, permitting them to develop their malignant phenotype fully and evade host immune attack. Gene expression signatures derived from non-neoplastic cells correlate well with response to initial and subsequent therapies, reflecting their functional relevance. Recent biomarker studies have added texture to clinical outcome predictors, and their incorporation into prognostic models may improve our understanding of the biologic correlates of treatment failure. Moreover, recent preclinical and clinical studies have demonstrated that the tumor microenvironment represents a promising therapeutic target, raising hope that novel treatment strategies focused on the interface between malignant and reactive cells will soon emerge.

Human Immunodeficiency Virus Infection and Hodgkin's Lymphoma in South Africa: An Emerging Problem

Hodgkin's lymphoma (HL) occurs with increasing frequency in human-immunodeficiency-virus-(HIV-) infected individuals. The natural history and behaviour of HIV-HL is different, being more atypical and aggressive. The association between HIV and HL appears to be primarily EBV driven. HAART use does not significantly impact on the incidence of HL. Indeed, the risk of HL has increased in the post-HAART era. However, the advent of HAART has brought renewed hope, allowing standard therapeutic options to be used more optimally, with better treatment outcomes. Despite the renewed optimism, the overall survival of HIV-HL patients remains less favourable than that in HIV-seronegative patients. This is particularly true in sub-Saharan Africa, where there is a significant burden of HIV/AIDS and where more than half the patients are HAART naive at diagnosis of HL. The similarities and differences of a South African cohort of HIV-HL are presented in this paper.

Pretargeting CD45 enhances the selective delivery of radiation to hematolymphoid tissues in nonhuman primates

Pretargeted radioimmunotherapy (PRIT) is designed to enhance the directed delivery of radionuclides to malignant cells. Through a series of studies in 19 nonhuman primates (Macaca fascicularis), the potential therapeutic advantage of anti-CD45 PRIT was evaluated. Anti-CD45 PRIT demonstrated a significant improvement in target-to-normal organ ratios of absorbed radiation compared with directly radiolabeled bivalent antibody (conventional radioimmunotherapy [RIT]). Radio-DOTA-biotin administered 48 hours after anti-CD45 streptavidin fusion protein (FP) [BC8 (scFv)(4)SA] produced markedly lower concentrations of radiation in nontarget tissues compared with conventional RIT. PRIT generated superior target:normal organ ratios in the blood, lung, and liver (10.3:1, 18.9:1, and 9.9:1, respectively) compared with the conventional RIT controls (2.6:1, 6.4:1, and 2.9:1, respectively). The FP demonstrated superior retention in target tissues relative to comparable directly radiolabeled bivalent anti-CD45 RIT. The time point of administration of the second step radiolabeled ligand (radio-DOTA-biotin) significantly impacted the biodistribution of radioactivity in target tissues. Rapid clearance of the FP from the circulation rendered unnecessary the addition of a synthetic clearing agent in this model. These results support proceeding to anti-CD45 PRIT clinical trials for patients with both leukemia and lymphoma.

131I anti-CD45 radioimmunotherapy effectively targets and treats T-cell non-Hodgkin lymphoma

Radioimmunotherapy (RIT) options for T-cell non-Hodgkin lymphomas (T-NHLs) are limited. We evaluated anti-CD45-RIT in human (h) and murine (m) T-NHL. CD45 was highly expressed on hT-NHL patient samples (median, 2.3 x 10(5) antigen-binding capacity units/cell) and hT-NHL cell lines (3.4 x 10(5) CD45 antigen-binding capacity units/cell). Biodistribution studies in hTNHL xenografts showed that (131)I-labeled BC8 (anti-hCD45) delivered 154% (P = .01) and 237% (P = .002) more radioiodine to tumor sites over control antibodies at 24 hours and 48 hours, respectively. Importantly, tumor sites targeted with (131)I-BC8 exhibited 2.5-fold (P = .05), 3.0-fold (P = .007), and 3.6-fold (P = .07) higher (131)I retention over the nontarget organs of lungs, liver, and kidneys, respectively (24 hours). Because the clinical use of anti-hCD45 would target both T-NHL and other hematolymphoid tissues, we evaluated the ability of anti-mCD45 to target mT-NHL. mT-NHL grafts targeted with anti-mCD45 correspondingly retained 5.3 (P < .001), 5.4 (P < .001), and 8.7 (P < .001) times the radioactivity in tumor sites compared with nontarget organs of lung, liver, and kidney. (131)I-labeled BC8 therapy yielded improved complete remission rates (75% vs 0%, P < .001) and progression-free survivals (median, 23 days vs 4.5 days, P < .001) compared with controls. These data indicate that the high CD45 expression of T-NHL allows reliable tumor targeting and disease control supporting anti-CD45 RIT for T-NHL patients.

Bone-marrow-derived cells that home to acoustic deafened cochlea preserved their hematopoietic identity

The high degree of bone marrow cell (BMC) plasticity has prompted us to test its restoration possibility in inner ear repair. Our aim was to determine the potential of these cells to transdifferentiate into specialized cochlea cell types after acoustic injury and BMC mobilization. Lethally irradiated mice were transplanted with BMCs from green fluorescent protein (GFP) transgenic mice and subjected to acoustic deafening 3 months later. In a separate experiment, stem cell factor and granulocyte colony-stimulating factor were administered to test the effect of BMC mobilization on bone marrow-derived cell (BMDC) transdifferentiation. All mice showed almost complete chimerism 3 months after bone marrow transplantation. Upon acoustic trauma, robust BMDC migration was observed in the deafened cochlea. GFP+ cell migration was most prominent during the first week after acoustic deafening, and these cells accumulated significantly at the spiral ligament, perilymphatic compartment walls, and limbus regions. Most of the BMDCs expressed CD45 and CD68 and were identified as macrophages. Upregulation of stromal-derived factor 1 (SDF-1) was also observed in the spiral ligament during the first week after acoustic deafening. Cytokine treatment resulted in increased BMC mobilization in the systemic circulation. However, the presence of any stem cell progenitors or the differentiation of BMDCs into any cell types expressing cochlea sensory, supporting, fibrocytic, or neuronal markers were not detected in the deafened cochlea. In conclusion, we have demonstrated the homing capability of BMDCs to the deafened cochlea, and these cells displayed mature hematopoietic properties without spontaneous transdifferentiation to any cochlea cell types after acoustic trauma or bone marrow mobilization.

The CD4+CD26- T-cell population in classical Hodgkin's lymphoma displays a distinctive regulatory T-cell profile

Little is known about the gene expression profile and significance of the rosetting CD4+CD26- T cells in classical Hodgkin's lymphoma (cHL). To characterize these T cells, CD4+CD26- and CD4+CD26+ T-cell populations were sorted from lymph node (LN) cell suspensions from nodular sclerosis HL (NSHL) and reactive LNs. mRNA profiles of stimulated and resting cell subsets were evaluated with quantitative RT-PCR for 46 genes. We observed a higher percentage of CD4+CD26- T cells in NSHL than in reactive LNs. The resting CD4+CD26- T cells in NSHL showed higher mRNA levels of CD25, CTLA4, OX40 and CCR4 compared with in LNs, supporting a regulatory T-cell (Treg) type, and this was validated by immunohistochemistry. Moreover, these cells showed low or no expression of the Th1- or Th2-related cytokines IL-2, IFN-gamma, IL-13, IL-12B, IL-4, and IL-5, and the chemoattractant receptor CRTH2. Besides Tregs, Th17 cells may exist in NSHL based on the significantly higher IL-17 mRNA level for both T-cell populations in NSHL. Upon stimulation in vitro, lack of upregulation of mRNA levels of most cytokine genes indicated an anergic character for the CD4+CD26- T-cell subset. Anergy fits with the Treg profile of these cells, probably explaining the immunosuppressive mechanism involved in NSHL.

Loss of naïve (CD45RA+) CD4+ lymphocytes during pediatric infection with feline immunodeficiency virus

Feline immunodeficiency virus (FIV) infection of cats is an animal model for the pathogenesis of CD4+ lymphopenia and thymus dysfunction in HIV-infected humans. Recently, a monoclonal antibody (755) was reported to recognize the feline homologue to CD45RA, allowing the enumeration of naïve T cells in cats. We tested the hypothesis that pediatric FIV infection would be associated with a selective loss of naïve CD4+ lymphocytes by inoculating newborn cats with a pathogenic clone of FIV (JSY3) or a related clone with an inactive ORF-A gene (JSY3-DeltaORFA), and compared the data to age-matched uninfected control cats. Both FIV inocula were associated with a reduction in the CD4-CD8 ratio (p=0.01), which was attributable to a disproportionate loss of naïve CD4+ cells (p=0.01) vs. naïve CD8+ cells. Therefore, the reduced CD4:CD8 ratio in FIV-infected juvenile cats is associated with a selective depletion of naïve CD4+ cells from the blood.

Role of growth hormone receptor signaling in osteogenesis from murine bone marrow progenitor cells

Growth hormone (GH) regulates many of the factors responsible for controlling the development of bone marrow progenitor cells (BMPCs). The aim of this study was to elucidate the role of GH in osteogenic differentiation of BMPCs using GH receptor null mice (GHRKO). BMPCs from GHRKO and their wild-type (WT) littermates were quantified by flow cytometry and their osteogenic differentiation in vitro was determined by cell morphology, real-time RT-PCR, and biochemical analyses. We found that freshly harvested GHRKO marrow contains 3% CD34 (hematopoietic lineage), 43.5% CD45 (monocyte/macrophage lineage), and 2.5% CD106 positive (CFU-F/BMPC) cells compared to 11.2%, 45%, and 3.4% positive cells for (WT) marrow cells, respectively. When cultured for 14 days under conditions suitable for CFU-F expansion, GHRKO marrow cells lost CD34 positivity, and were markedly reduced for CD45, but 3- to 4-fold higher for CD106. While WT marrow cells also lost CD34 expression, they maintained CD45 and increased CD106 levels by 16-fold. When BMPCs from GHRKO mice were cultured under osteogenic conditions, they failed to elongate, in contrast to WT cells. Furthermore, GHRKO cultures expressed less alkaline phosphatase, contained less mineralized calcium, and displayed lower osteocalcin expression than WT cells. However, GHRKO cells displayed similar or higher expression of cbfa-1, collagen I, and osteopontin mRNA compared to WT. In conclusion, we show that GH has an effect on the proportions of hematopoietic and mesenchymal progenitor cells in the bone marrow, and that GH is essential for both the induction and later progression of osteogenesis.

alpha2,6-Sialylation promotes binding of placental protein 14 via its Ca2+-dependent lectin activity: insights into differential effects on CD45RO and CD45RA T cells

Placental protein 14 (PP14; glycodelin) is a pregnancy-associated immunoregulatory protein that is known to inhibit T cells via T-cell receptor desensitization. The recent demonstration of PP14 as lectin has provided insight into how it may mediate its CD45 glycoprotein-dependent T-cell inhibition. In this study, we have investigated PP14's lectin-binding properties in detail. Significantly, PP14 reacts with N-acetyllactosamine (LacNAc) as was also found for members of the galectin family, such as the potent immunoregulatory protein, galectin-1. However, in contrast to galectin-1, PP14's binding is significantly enhanced by alpha2,6-sialylation and also by the presence of cations. This was demonstrated by preferential binding to fetuin as compared with its desialylated variant asialofetuin (ASF) and by using free alpha2,6- versus alpha2,3-sialylated forms of LacNAc in competitive inhibition and direct solid-phase binding assays. Interestingly, from immunological point of view, PP14 also binds differentially to CD45 isoforms known to differ in their degree of sialylation. PP14 preferentially inhibits CD45RA+, as compared with CD45RO+ T cells, and preferentially co-capped this variant CD45 on the T-cell surface. Finally, we demonstrate that PP14 promotes CD45 dimerization and clustering, a phenomenon that may regulate CD45 activity.

CD45 expression on rat acinar cells: Involvement in pro-inflammatory cytokine production

CD45 transduces activation signals in inflammatory cells. We investigate CD45 expression on pancreatic acinar cells and examine its role in the inflammatory response which these cells have also shown under certain circumstances. Similar CD45 mRNA levels were found in acinar cells and leukocytes (positive control). Flow cytometric and immunohistochemical analysis showed a heterogeneous CD45 distribution on acinar cells. Activation of acinar cells by incubation with pancreatitis-associated ascitic fluid as evidencied by TNF-alpha production resulted in a decreased CD45 expression, suggesting that CD45 acts as a negative regulator of cytokine production. As a validation of this finding in vivo, a decrease in the acinar CD45 expression in parallel with an increased ability to produce TNF-alpha was found in rats with acute pancreatitis. Our data show that CD45 is constitutively expressed in acinar cells and suggest that it plays an important role in negatively regulating cytokine production.

Characterization of a monoclonal antibody identifying a CD45RA antigen on feline leukocytes

The antibody produced by a murine hybridoma obtained from the fusion of SP2/0 plasmacytoma cells with splenocytes of a mouse immunized with feline bone marrow was found to react with 60% of bone marrow cells and 80% of peripheral blood leukocytes (PBL); reactivity in the latter tissue was restricted almost entirely to mononuclear cells. Two-color FACScan analyses of this antibody with mAbs specific for feline lymphocytes revealed positive and negative populations of CD4 and CD8 cells. The reactivity for CD4 and CD8 cells was animal age dependent, binding to a higher percentage of the cells in young (2-9 months) versus older animals (> 4 years). In a mitogen driven assay for IgG production by PBL the addition of this antibody to the cultures enhanced the suppressor activity of CD8 cells, a function attributed to activation of a CD4 suppressor-inducer population; removal of CD8 cells negated any induction of suppression. Mild papain digestion of bone marrow and PBL completely removed the antigen detected by this antibody while not affecting reactivity of a pan-T antibody. Western blot analysis showed binding of the antibody to polypeptides of approximately 200 kDa on feline bone marrow and PBL. The data suggest that this mAb is identifying the feline homologue of the leukocyte common antigen of cells with a functional specificity characteristic of a CD45RA isoform.

Interleukin 4 production by peripheral blood lymphocytes in patients with classical Hodgkin lymphoma

Although the production of interleukin (IL) 2 and interferon (IFN) gamma by peripheral blood lymphocytes in patients with Hodgkin lymphoma (HL) is well documented, the synthesis of IL4 has not been investigated before. The present study examines the production of IL4 by 2-day phytohaemaglutinin (PHA)-stimulated peripheral blood (PB) cells in HL and correlates the cytokine levels with the proportion of the different T-cell sub-populations. We observed a significant increase in the mean level of production of IL4 in patients with HL when compared with normal controls. The increased amount of IL4 in patients with HL correlated significantly with the proportion of the CD3(+)CD8(+) cells but not with CD3(+)CD4(+). The intensity of cytoplasmic IL4 (expressed as relative median fluorescence (RMF)) was significantly higher in the CD3(+)CD8(+) cells of the patients with HL compared with the CD3(+)CD4(+) sub-population, or with the normal CD3(+)CD8(+) cells and correlated with the levels of IL4 release in culture supernatants. In conclusion, there is increased production of IL4 by PHA-activated PB lymphocytes in HL. The CD3(+)CD8(+) T-cell population appears to be responsible for this increased synthesis.

Complement-fixing CD45 monoclonal antibodies to facilitate stem cell transplantation in mouse and man

Broadening the applicability of stem cell therapies requires safer preparative regimens for patients. The CD45 antigen is present on all cells of the hematopoietic lineage, and using a murine model, we determined whether a lytic CD45 monoclonal antibody could produce persistent aplasia and whether it could facilitate syngeneic or allogeneic stem cell engraftment. After its systemic administration, we found that all leukocyte subsets in peripheral blood were markedly diminished, but only the effect on the lymphoid compartment was sustained and marrow progenitor cells were spared from destruction. Given the transient effects of the monoclonal antibody on myelopoiesis and the more persistent effects on lymphopoiesis, we asked whether this agent could contribute to donor hemopoietic engraftment after subablative transplantation. Treatment with anti-CD45 alone did not enhance syngeneic engraftment, consistent with its inability to destroy progenitor cells and permit competitive repopulation with syngeneic donor stem cells. By contrast, the combination of anti-CD45 and an otherwise inactive dose of total-body irradiation allowed engraftment of H2 fully allogeneic donor stem cells. We attribute this result to the recipient immunosuppression produced by depletion of CD45-positive lymphocytes. We next assessed a pair of unconjugated rat anti-human CD45 monoclonal antibodies (MAbs), YTH54.12 and YTH25.4, in a clinical trial in patients who were to receive stem cell transplantation for acute leukemia. The maximum tolerated dose of these MAbs, 400 microg/kg/day, produced a pattern of response identical to that seen in the mice, with marked reductions in circulating lymphoid and myeloid cells and sparing of early marrow progenitors. In two of three patients with active leukemia, the MAbs also produced a decrease in the percentage of leukemic blast cells in bone marrow. These pre-clinical and clinical results warrant further evaluation of anti-CD45 MAbs in subablative preparative regimens for stem cell transplantation.

Hematopoietic and immunomodulatory effects of lytic CD45 monoclonal antibodies in patients with hematologic malignancy

The CD45 antigen is present on all cells of the hematopoietic lineage. In some rodent models, lytic CD45 monoclonal antibodies (MAbs) induce complete marrow aplasia. In others, only transient myelolymphodepletion are observed, which are nonetheless sufficient to permit engraftment with fully allogeneic stem cells after otherwise ineffective doses of radiation. The in vivo effects of unconjugated cytolytic CD45 MAbs on myeloid and lymphoid cells in humans are unknown, so it is unclear if they could contribute in a similar way to conventional ablative or to nonmyeloablative preparative regimens used for stem cell transplantation (SCT). We therefore assessed the safety, myeloreductive activities, and lymphoreductive activities of the unconjugated rat anti-human CD45 MAbs, YTH25.4 and YTH54.12, in subjects who were to undergo SCT for advanced hematologic malignancy. The MAb pair bind to contiguous but nonoverlapping epitopes on CD45 and work synergistically to fix complement and recruit cellular lytic mechanisms. The MAbs were given in increasing doses up to 1600 microg/kg during 4 days, after which the patients began their conventional transplantation preparative regimen. The maximum tolerated dose of these MAbs, 400 microg/kg/d, produced marked reduction in circulating lymphoid and myeloid cells while largely sparing marrow progenitors. In 2 of 3 patients who had active leukemia at the time of study, the MAbs reduced the percentage of leukemic blast cells in bone marrow. Seven of 14 patients are disease free 610 to 1555 days post-SCT. The in vivo myeloreductive and lymphoreductive properties of lytic CD45 MAb in humans, therefore, closely parallel the activity seen in a murine model and, therefore, may be of similar value.

Anti-CD45-mediated cytoreduction to facilitate allogeneic stem cell transplantation

The CD45 antigen is present on all cells of the hematopoietic lineage. Using a murine model, we have determined whether a lytic CD45 monoclonal antibody can produce persistent aplasia and whether it could facilitate syngeneic or allogeneic stem cell engraftment. After its systemic administration, we found saturating quantities of the antibody on all cells expressing the CD45 antigen, both in marrow and in lymphoid organs. All leukocyte subsets in peripheral blood were markedly diminished during or soon after anti-CD45 treatment, but only the effect on the lymphoid compartment was sustained. In contrast to the prolonged depletion of T and B lymphocytes from the thymus and spleen, peripheral blood neutrophils began to recover within 24 hours after the first anti-CD45 injection and marrow progenitor cells were spared from destruction, despite being coated with saturating quantities of anti-CD45. Given the transient effects of the monoclonal antibody on myelopoiesis and the more persistent effects on lymphopoiesis, we asked whether this agent could contribute to donor hematopoietic engraftment following nonmyeloablative transplantation. Treatment with anti-CD45 alone did not enhance syngeneic engraftment, consistent with its inability to destroy progenitor cells and permit competitive repopulation with syngeneic donor stem cells. By contrast, the combination of anti-CD45 and an otherwise inactive dose of total-body irradiation allowed engraftment of H2 fully allogeneic donor stem cells. We attribute this result to the recipient immunosuppression produced by depletion of CD45(+) lymphocytes. Monoclonal antibodies of this type may therefore have an adjunctive role in nonmyeloablative conditioning regimens for allogeneic stem cell transplantation.

Chemokines, cytokines and their receptors in Hodgkin's lymphoma cell lines and tissues

BACKGROUND

Hodgkin's lymphoma (HL) is characterized by a minority of neoplastic cells, the so-called Reed-Sternberg (RS) cells, and an admixture of reactive cells including lymphocytes, plasma cells, eosinophils and histiocytes. Cytokines produced in HL, either by RS or infiltrating cells, might explain the presence and maintenance of an impaired immune response. Chemokines (cytokines with chemoattractant properties) produced by RS cells play a major role in leukocyte trafficking. These molecules with specific receptor affinities contribute, for example by attracting TH2-like T cells, to the maintenance of a favorable environment for survival of RS cells.

RESULTS AND DISCUSSION

Cross-talk between RS cells and reactive elements involves several cytokine/chemokines that process proliferative [interleukin (IL)-13 and IL-17], immunosuppressive (IL-10 and transforming growth factor-beta) and background formation (IL-5, TARC, MDC, IP-10, RANTES, Mig and others) messages. These autocrine and paracrine interactions lead to an environment where RS cells are able to proliferate, escape from apoptosis and survive host anti-tumor defense.

CONCLUSIONS

The proper modulation of these complex pathways may allow the development of new strategies in HL therapy.

Hyposialated 185 kDa CD45RA+ molecules attain a high concentration in B lymphoma cells and in activated human B cells

Alternate splicing of exons of the CD45 molecule generates multiple isoforms differing in their molecular weights (MWs). In B-lymphocytes the CD45RA isoform was previously shown to be expressed on glycoproteins with MWs of 220 and 205 kDa, while the CD45RO isoform was expressed on glycoproteins with MW of 180 kDa. The present study demonstrated that B cell lymphomas and activated B-cells contain CD45 molecules with a MW of 185 kDa that express the CD45RA and CD45RC specificities but neither the CD45RB nor the CD45RO specificities. 185 kDa CD45RA+ molecules were detected in B cell lymphoma B lines, in Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines, and in tonsillar B cells, but not in normal, unstimulated peripheral blood B cells. These molecules were not detected in neoplastic and normal T cells. CD45RA+ 185 kDa molecules were present in B cells from three non-Hodgkin's patients in leukemic phase were not detected in B lymphocytes of seven of nine CLL patients tested. Trypsin treatment eliminated only 220 kDa CD45RA+ molecules but not 185 kDa CD45RA+ molecules, indicating that the 185 kDa CD45RA+ molecules are not expressed on the cell surface. Pulse-chase experiments, and studies on the effects of tunicamycin, neuraminidase and O-glycosidase, indicated that the 185 kDa molecules are partially glycosylated CD45RABC molecules that constitute precursors of the 220 kDa molecules. The high concentration of 185 kDa CD45RA+ molecules in B lymphoma cells and in activated B cells seems to reflect a high turnover of CD45RA+ molecules characteristic for these cells.

Regulation of the expression of CD45 isoforms in the Farage human B cell lymphoma line and its 10.6.1 subline

Different B-cell neoplasias vary in the expression of CD45 isoforms. In the present study two sublines of a human B cell lymphoma- the original Farage line (Farage OL) and the Farage 10.6.1 subline were used to analyze the regulation of the expression of CD45 cell surface determinants. Cells of the Farage OL line constitutively expressed both CD45RO and CD45RA determinants on their cell surface. In contrast, the majority of the cells of the Farage 10.6.1 subline expressed CD45RA, and only few cells were CD45RO+. The low molecular spliced CD45 mRNA, characteristic for CD45RO was found in Farage OL cells, but was almost undetectable in Farage 10.6.1 cells. Following exposure to interleukin-4 (IL-4) a large proportion of the Farage 10.6.1 cells expressed CD45RO while in Farage OL cells the proportion of CD45RO+ was slightly reduced. The low molecular, spliced mRNA characteristic for CD45RO, was increased in Farage 10.6.1 cells following IL4 stimulation, but was slightly reduced in Farage OL cells. The molecular weight of CD45RA molecules produced by Farage cells varied from 185 kDa to 220 kDa while that of CD45RO molecules was 175 kDa. Preliminary attempts were made to determine a possible correlation between the expression of CD45RO and apoptosis in Farage cells. In both the Farage OL and Farage 10.6.1 cells the proportion of Bcl-2+ cells was lower among CD45RO+ cells than among CD45RO- cells. The present study indicates that IL4 has different effects on the alternative splicing of CD45 mRNA in two closely related B cell lymphoma lines. Thus, factors produced by the B lymphoma cells themselves may endow the cells with different patterns of responsiveness to a single stimulatory agent.

High expression of the CC chemokine TARC in Reed-Sternberg cells. A possible explanation for the characteristic T-cell infiltratein Hodgkin's lymphoma

Hodgkin's lymphoma is characterized by the combination of Reed-Sternberg (R-S) cells and a prominent inflammatory cell infiltrate. One of the intriguing questions regarding this disease is what is causing the influx of T lymphocytes into the involved tissues. We applied the serial analysis of gene expression (SAGE) technique on the Hodgkin's lymphoma-derived cell line L428 and on an Epstein-Barr virus (EBV)-transformed lymphoblastoid B-cell line. A frequently expressed tag in L428 corresponded to the T-cell-directed CC chemokine TARC. Reverse transcription polymerase chain reaction analyses demonstrated expression of TARC in nodular sclerosis (NS) and mixed cellularity (MC) classical Hodgkin's lymphomas but not in NLP Hodgkin's lymphoma, anaplastic large-cell lymphomas, and large-B-cell lymphomas with CD30 positivity. Two of five cases of T-cell-rich B-cell lymphoma (TCRBCL) were TARC positive. RNA in situ hybridization (ISH) showed a strong signal for TARC in the cytoplasm of R-S cells, and immunohistochemical staining confirmed the presence of the TARC protein in the R-S cells of NS and MC Hodgkin's lymphomas. The lymphocytic and histiocytic (L&H)-type cells of nodular lymphocyte predominance Hodgkin's lymphoma and the neoplastic cells of non-Hodgkin's lymphomas with the exception of two cases of TCRBCL did not stain for TARC. TARC is known to bind to the CCR4 receptor, which is expressed on activated Th2 lymphocytes. The immunophenotype of lymphocytes surrounding R-S cells is indeed Th2-like, and by RNA ISH these lymphocytes showed a positive signal for the chemokine receptor CCR4. The findings suggest that production of TARC by the R-S cells may explain the characteristic T-cell infiltrate in classical Hodgkin's lymphoma.

Immune escape mechanisms in Hodgkin's disease

BACKGROUND

The nodular sclerosis and mixed cellularity subtypes of Hodgkin's disease are histologically characterised by a small population of neoplastic cells, the so-called Reed-Sternberg cells and their mononuclear variants (RS cells) and an extensive admixture of other cell types including lymphocytes, plasma cells, eosinophils, and histiocytes. The nature of this infiltrate is largely known, but the mechanisms and functional effects are not. The small lymphocytes immediately surrounding the RS cells are mostly CD4+ T cells that express early activation markers. The absence of prominent specific cytotoxic T cell or natural killer (NK) cell populations seems to argue against a Th1-type response, whereas the sometimes prominent admixture of plasma cells and eosinophils is suggestive of a Th2-type response. Enrichment of the CD4 T-cell population may result from selective influx of CD4 T cells or from selective depletion of CD8 and NK cells.

RESULTS AND DISCUSSION

The T cells surrounding RS cells have an immuno-phenotype and cytokine production capability consistent with a Th2-type response. RS cells express several members of the TNF receptor family such as the FAS ligand (CD95L) that may induce apoptosis of activated, FAS expressing, CD8+ T cells and NK cells. The RS cells also produce TGF beta and interleukin-10 that may downmodulate the Th1 response. In addition, the Reed-Sternberg cells produce the chemokine TARC that could lead to the specific attraction of a Th2 T-cell subset.

CONCLUSION

RS cells have several mechanisms that may allow it to escape an effective immune response. The relative contributions of each of these and other potential mechanisms are not yet known.

The role of CD45 and CD45-associated molecules in T cell activation

CD45 (lymphocyte common antigen) is a receptor-linked protein tyrosine phosphatase that is expressed on all leucocytes, and which plays a crucial role in the function of these cells. On T cells the extracellular domain of CD45 is expressed in several different isoforms, and the particular isoform(s) expressed depends on the particular subpopulation of cell, their state of maturation, and whether or not they have previously been exposed to antigen. It has been established that the expression of CD45 is essential for the activation of T cells via the TCR, and that different CD45 isoforms display a different ability to support T cell activation. Although the tyrosine phosphatase activity of the intracellular region of CD45 has been shown to be crucial for supporting signal transduction from the TCR, the nature of the ligands for the different isoforms of CD45 have been elusive. Moreover, the precise mechanism by which potential ligands may regulate CD45 function is unclear. Interestingly, in T cells CD45 has been shown to associate with numerous molecules, both membrane associated and intracellular; these include components of the TCR-CD3 complex and CD4/CD8. In addition, CD45 is reported to associate with several intracellular protein tyrosine kinases including p56lck and p59fyn of the src family, and ZAP-70 of the Syk family, and with numerous proteins of 29-34 kDa. These CD45-associated molecules may play an important role in regulating CD45 tyrosine phosphatase activity and function. However, although the role of some of the CD45-associated molecules (e.g. CD45-AP and LPAP) has become better understood in recent years, the role of others still remains obscure. This review aims to summarize recent findings on the role of CD45 and CD45-associated molecules in T cell activation, and to highlight issues that seem relevant to ongoing research in this area.

Immunology of Hodgkin's disease

Hodgkin's disease is characterized by an immune response in the involved tissues that is predominantly CD4 mediated. The CD4+ T-cells are CD45RO+ and CD45RBdim, they express several activation markers but lack CD26, and in vitro can be stimulated to produce gamma-interferon and IL-4, but not IL-2. This is not the usual immunophenotype and cytokine production pattern of Th1, Th2 or Th0 cells and may be a reflection of anergy. The cause of such an anergic reaction is not clear since RS cells express HLA class II as well as the co-stimulator molecules CD80 and CD86. It is possible that a (hypothetical) super antigen expressed on the RS cells may play a role. The absence of IL-2 production however explains the absence of a CD8 mediated response. In addition to that, RS cells generally do not express HLA class I, which allows them to escape CD8 mediated responses. The link between the ineffective immune response in the tissue and the generalized immune deficiency in Hodgkin's disease may consist of several components. These include the influx of mature T-cells into the affected tissues, the secretion of inhibitory molecules by the neoplastic cells and the spill-over of the anergic T-cell response into the general circulation by either the Hodgkin related antigen or also as a result of an IL-4 dominated response. The latter possibility may also be related to the hyper-gamma-globulinaemia and the frequently observed high IgE levels.