Disruption of memory B-cell trafficking by belimumab in patients with systemic lupus erythematosus.

OBJECTIVES: Autoreactive memory B cells contribute to chronic and progressive courses in autoimmune diseases like systemic lupus erythematosus (SLE). The efficacy of belimumab (BEL), the first approved biologic treatment for SLE and lupus nephritis (LN), is generally attributed to depletion of activated naïve B cells and inhibition of B cell activation. BEL's effect on memory B cells (MBCs) is currently unexplained. We performed an in-depth cellular and transcriptomic analysis of BEL's impact on the blood MBC compartment in patients with SLE. METHODS: A retrospective meta-analysis was conducted, pooling flow cytometry data from four randomized trials involving 1245 patients with SLE treated with intravenous BEL or placebo. Then, extensive MBC phenotyping was performed using high-sensitivity flow cytometry in patients with mild/moderate SLE and severe SLE/LN treated with subcutaneous BEL. Finally, transcriptomic characterization of surging MBCs was performed by single-cell RNA sequencing. RESULTS: In BEL-treated patients, a significant increase in circulating MBCs, in a broad range of MBC subsets, was established at week 2, gradually returning to baseline by week 52. The increase was most prominent in patients with higher SLE disease activity, serologically active patients, and patients aged ≤18 years. MBCs had a non-proliferating phenotype with a prominent decrease in activation status and downregulation of numerous migration genes. CONCLUSION: Upon BEL initiation, an increase of MBCs was firmly established. In the small cohort investigated, circulating MBCs were de-activated, non-proliferative, and demonstrated characteristics of disrupted lymphocyte trafficking, expanding on our understanding of the therapeutic mechanism of B cell-activating factor inhibition by BEL. TRIAL REGISTRATION: ClinicalTrials.gov NCT00071487, NCT00410384, NCT01632241, NCT01649765, NCT03312907, NCT03747159.

A transcriptomic based deconvolution framework for assessing differentiation stages and drug responses of AML.

The diagnostic spectrum for AML patients is increasingly based on genetic abnormalities due to their prognostic and predictive value. However, information on the AML blast phenotype regarding their maturational arrest has started to regain importance due to its predictive power for drug responses. Here, we deconvolute 1350 bulk RNA-seq samples from five independent AML cohorts on a single-cell healthy BM reference and demonstrate that the morphological differentiation stages (FAB) could be faithfully reconstituted using estimated cell compositions (ECCs). Moreover, we show that the ECCs reliably predict ex-vivo drug resistances as demonstrated for Venetoclax, a BCL-2 inhibitor, resistance specifically in AML with CD14+ monocyte phenotype. We validate these predictions using LUMC proteomics data by showing that BCL-2 protein abundance is split into two distinct clusters for NPM1-mutated AML at the extremes of CD14+ monocyte percentages, which could be crucial for the Venetoclax dosing patients. Our results suggest that Venetoclax resistance predictions can also be extended to AML without recurrent genetic abnormalities and possibly to MDS-related and secondary AML. Lastly, we show that CD14+ monocytic dominated Ven/Aza treated patients have significantly lower overall survival. Collectively, we propose a framework for allowing a joint mutation and maturation stage modeling that could be used as a blueprint for testing sensitivity for new agents across the various subtypes of AML.

Autoantibody subclass predominance is not driven by aberrant class switching or impaired B cell development.

A subset of autoimmune diseases is characterized by predominant pathogenic IgG4 autoantibodies (IgG4-AID). Why IgG4 predominates in these disorders is unknown. We hypothesized that dysregulated B cell maturation or aberrant class switching causes overrepresentation of IgG4+ B cells and plasma cells. Therefore, we compared the B cell compartment of patients from four different IgG4-AID with two IgG1-3-AID and healthy donors, using flow cytometry. Relative subset abundance at all maturation stages was normal, except for a, possibly treatment-related, reduction in immature and naïve CD5+ cells. IgG4+ B cell and plasma cell numbers were normal in IgG4-AID patients, however they had a (sub)class-independent 8-fold increase in circulating CD20-CD138+ cells. No autoreactivity was found in this subset. These results argue against aberrant B cell development and rather suggest the autoantibody subclass predominance to be antigen-driven. The similarities between IgG4-AID suggest that, despite displaying variable clinical phenotypes, they share a similar underlying immune profile.

Immune Determinants of Viral Clearance in Hospitalised COVID-19 Patients: Reduced Circulating Naïve CD4+ T Cell Counts Correspond with Delayed Viral Clearance.

Virus-specific cellular and humoral responses are major determinants for protection from critical illness after SARS-CoV-2 infection. However, the magnitude of the contribution of each of the components to viral clearance remains unclear. Here, we studied the timing of viral clearance in relation to 122 immune parameters in 102 hospitalised patients with moderate and severe COVID-19 in a longitudinal design. Delayed viral clearance was associated with more severe disease and was associated with higher levels of SARS-CoV-2-specific (neutralising) antibodies over time, increased numbers of neutrophils, monocytes, basophils, and a range of pro-inflammatory cyto-/chemokines illustrating ongoing, partially Th2 dominating, immune activation. In contrast, early viral clearance and less critical illness correlated with the peak of neutralising antibodies, higher levels of CD4 T cells, and in particular naïve CD4+ T cells, suggesting their role in early control of SARS-CoV-2 possibly by proving appropriate B cell help. Higher counts of naïve CD4+ T cells also correlated with lower levels of MIF, IL-9, and TNF-beta, suggesting an indirect role in averting prolonged virus-induced tissue damage. Collectively, our data show that naïve CD4+ T cell play a critical role in rapid viral T cell control, obviating aberrant antibody and cytokine profiles and disease deterioration. These data may help in guiding risk stratification for severe COVID-19.

Prolonged activation of nasal immune cell populations and development of tissue-resident SARS-CoV-2-specific CD8+ T cell responses following COVID-19.

Systemic immune cell dynamics during coronavirus disease 2019 (COVID-19) are extensively documented, but these are less well studied in the (upper) respiratory tract, where severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replicates1-6. Here, we characterized nasal and systemic immune cells in individuals with COVID-19 who were hospitalized or convalescent and compared the immune cells to those seen in healthy donors. We observed increased nasal granulocytes, monocytes, CD11c+ natural killer (NK) cells and CD4+ T effector cells during acute COVID-19. The mucosal proinflammatory populations positively associated with peripheral blood human leukocyte antigen (HLA)-DRlow monocytes, CD38+PD1+CD4+ T effector (Teff) cells and plasmablasts. However, there was no general lymphopenia in nasal mucosa, unlike in peripheral blood. Moreover, nasal neutrophils negatively associated with oxygen saturation levels in blood. Following convalescence, nasal immune cells mostly normalized, except for CD127+ granulocytes and CD38+CD8+ tissue-resident memory T cells (TRM). SARS-CoV-2-specific CD8+ T cells persisted at least 2 months after viral clearance in the nasal mucosa, indicating that COVID-19 has both transient and long-term effects on upper respiratory tract immune responses.

Evaluation of circulating tumor cells in colorectal cancer using flow cytometry.

OBJECTIVE: We aimed to evaluate the prognostic value of circulating tumor cells (CTCs) and the impact of intraoperative tumor manipulation on CTCs in colorectal cancer (CRC) patients. METHODS: We performed a prospective study on 40 patients with CRC stages I to IV who received curative surgery using the no-touch technique. Flow cytometry was used to identify CTCs in peripheral blood samples (4 mL/sample) collected at two surgical moments: skin incision (T1) and after surgical resection (T2). A threshold of ≥4 CTCs/4 mL blood was established for considering patients CTC positive. RESULTS: In the univariate analysis, CTC evaluation at T2 was correlated with female sex, vascular invasion, tumor localization in the colon and metastatic lymph nodes. In the multivariate analysis, only female sex and colon cancer maintained statistical significance. At a medium follow-up of 15 months (1-25 months), the mortality rate was 10% (n = 4), with no significant differences between the overall survival of T1 or T2 CTC-positive and CTC-negative patients. CONCLUSIONS: Flow cytometry is a feasible CTC identification technique in CRC, and although surgical manipulation has no influence on CTC numbers, CTCs may serve as a prognostic and predictive factor.

The MHC-II antigen presentation machinery and B7 checkpoint ligands display distinctive patterns correlated with acute myeloid leukaemias blast cells HLA-DR expression.

Acute Myeloid Leukaemia (AML) is a neoplasia characterised by rapid proliferation and an increased rate of relapses. The AML blasts display features of antigen-presenting cells (APC), and thus can directly modulate the anti-tumour T cell responses. The bone marrow of a group consisting of 30 newly diagnosed patients and four healthy donors (HD) was investigated for the expression of HLA-DR, several molecules involved in MHC-II antigen-presentation and MHC-II groove editing, like HLA-DM, CD74 and CLIP, as well as a set of immune checkpoint ligands, like ICOS-L, B7.2, PD-L2 and B7-H3. The patients were further characterised for their genetic anomalies and distributed to favourable, intermediate and adverse ELN risk categories. We were able to show that while 23% of our patients displayed a low level of HLA-DR surface expression, all patients displayed higher HLA-DM and CD74 expression compared to HD. However, a higher CLIP expression was noticed only in the HLA-DR low patients. The co-inhibitory PD-L2 and B7-H3 molecules were increased in the cases with normal HLA-DR expression; oppositely, the co-stimulatory ICOS-L and the dual function B7.2 were significantly increased in the cases with HLA-DR low expression. Furthermore, no favourable ELN risk cases were found within the HLA-DR low group. All in all, these data show that the AML with low versus normal HLA-DR expression display different profiles of MHC class II machinery molecules and B7 ligands, which are correlated with distinct ELN stratification. Furthermore, as our study included healthy individuals, it offers valuable information about the expression levels that should be considered as normal for these markers known to cause differences in peptide repertoires, reflected further in distinct T-cells polarisation pathways.

B7-Positive and B7-Negative Acute Myeloid Leukemias Display Distinct T Cell Maturation Profiles, Immune Checkpoint Receptor Expression, and European Leukemia Net Risk Profiles.

Acute myeloid leukemia (AML) is generally considered a poorly immunogenic malignancy, displaying a "non-inflamed" leukemia microenvironment (LME), leading to T cell tolerance. However, the immune landscape of AML is much more heterogeneous. Since B7 expression is regarded as a consequence of an interferon-mediated "inflammatory" phenotype, we have investigated by flow cytometry the B7 checkpoint ligands B7.1, B7.2, programmed death ligand 1 (PD-L1), PD-L2, ICOS-L, B7-H3, and B7-H4 on the AML blasts of 30 newly diagnosed patients and their corresponding receptors [cytotoxic T lymphocyte-associated protein 4 (CTLA-4), programmed death 1 (PD-1), and inducible T cell costimulator (ICOS)] on bone marrow (BM) T cell maturation populations. We could thus evidence B7-negative and B7-positive leukemias either with an isolated expression or part of eight different checkpoint ligand "signatures" that always included an inhibitory B7 molecule. B7-positive AMLs encompassed intermediate and adverse European Leukemia Net (ELN) risk cases and displayed mainly central memory CD4+ T cells with high ICOS levels and effector CD8+ T cells with high PD-1 expression. B7-negative cases were rather classified as AML with recurrent genetic anomalies and displayed predominantly naive T cells, with the exception of NPM1 mutated AMLs, which expressed B7-H3. These different B7 immune profiles suggest that specific immunotherapies are required to target the distinct immune evasion strategies of this genetically heterogeneous disease.

CONCENTRATIONS OF VITREAL CYTOKINES IN RHEGMATOGENOUS RETINAL DETACHMENT.

UNLABELLED: Proliferative vitreoretinopathy (PVR) is one of the most frequent causes of failure of rhegmatogenous retinal detachment (RRD) surgery. AIM: To measure the vitreous levels of granulocyte colony stimulating factor (G-CSF) and monocyte chemoattractant protein 1 (MCP-1) in eyes with RRD and in a control group. MATERIAL AND METHODS: A prospective study of 40 patients operated for RRD (study group) and 20 patients with epiretinal membrane or macular holes (selected as control group since they needed vitrectomy but had attached retinas). Vitreous samples were collected during vitrectomy and were assessed for the presence of cytokines using a fluorescent bead-based multiplex assay. RESULTS: The concentration of G-CSF (8.59 pg/ml) and MCP-1 (1615.2 pg/ml) were significantly increased in the study group, when compared to the control group (0 and 469.13 pg/ml, respectively). MCP-1 was also significantly increased in the subgroup of patients with PVR compared to the patients with uncomplicated RRD. CONCLUSIONS: The levels of these biomarkers support the idea that proliferative vitreoretinopathy has an inflammatory component.

Report of a successful ongoing pregnancy as a result of IMSI with assisted oocyte activation.

We report a successful ongoing pregnancy obtained in a case of total globozoospermia after intracytoplasmic morphologically selected sperm injection (IMSI) with oocyte activation. The first semen analysis on investigation showed partial globozoospermia. However, under high magnification assessment at oocyte retrieval only round headed sperm were observed. Considering the high risk of a complete failure to fertilize from IMSI the couple gave written informed consent to the use of oocyte activation media post IMSI. One embryo fertilized, developed to a hatching blastocyst and was transferred resulting in an ongoing pregnancy. This successful outcome shows the use of IMSI is useful in the evaluation of total globozooozpermia and therefore aids in the justification of the use of oocyte activation media.

It's Never over until It's over: How Can Age and Ovarian Reserve Be Mathematically Bound through the Measurement of Serum AMH-A Study of 5069 Romanian Women.

Wide regional differences in the age-related Anti Mullerian hormone (AMH) regression patterns or age at onset of natural menopause have been reported, possibly reflecting genetic, socioeconomic, environmental, racial or ethnic peculiarities. Moreover, adaptation of AMH levels from different assays using regression functions may lack accuracy and externally defined references for AMH levels may not fully comply with a specific geographical area. The current study aimed to establish an accurate mathematical relationship between AMH serum values and age in a large group of women from Romania, as any consistent difference from previously reported regression models may aid in building specific profiles for the AMH decline with age in this geographical region. Our study pointed out to the quadratic regression as the most fitted pattern of correlation for all the age groups between 24 and 45. To our knowledge the current manuscript is based on the singular study carried out in this geographical region, generating a particular age-related pattern of association between age and serum AMH levels in women, regardless of their subjacent pathologies.

Optimization of culture conditions for bone marrow stromal cells in RPMI-1640 medium.

UNLABELLED: Bone marrow mesenchymal stem cells are important for both research and clinical purpose. A number of culture methods for these cells are available on the market, many of them consisting of specialized growing media in combination with growth factors. Our goal was to optimize a less expensive culture method for bone marrow mesenchymal cells. MATERIAL AND METHODS: Eight samples of bone marrow aspirates from patients were used. Out these 8 samples 2 were from healthy people, 3 from chronic granulocytic leukemia patients, 2 from multiple myeloma patients and 2 from patients with myelodysplastic syndrome. Bone aspirates from healthy people were used to optimize the culture method and the rest were used for testing the optimized method. Two methods were tried: 1. Cell culture starting from whole bone marrow, 2) cell culture after bone marrow separation in density gradient with Histopaque. RESULTS: Cell culture starting from whole bone marrow gives better yields for mesenchymal stem cells than methods which include gradient density separation of mononuclear cells with Ficoll-Histopaque. CONCLUSIONS: We have optimised a less expensive cell culture method for bone marrow mesenchymal cells.

[Prognostic significance of leukemia-associated phenotype in correlation with other biologic markers in acute myeloid leukemia patients]. / Identificarea semnificatiei prognostice a fenotipului asociat leucemiei in corelatie cu alti markeri biologici la pacientii cu leucemie acuta mieloblastica.

UNLABELLED: Leukemic cells have unique aberrant phenotypes, which permit identification of this cells at diagnose and in evolution of the disease. Signaling molecules with other cells and bone marrow stroma are part of the leukemic cells phenotype. Genetic and molecular abnormalities have the main prognostic significance and confer the leukemic cell status. The main aim of the current study is to identify correlation between recognized prognostic factors in acute myeloid leukemia (AML) patients and other phenotypic markers. MATERIAL AND METHOD: Imunophenotypic analysis (BDFACS CantoII, FACSDiva Software) was performed on peripheral blood/bone marrow aspirate samples of 56 patients diagnosed with AML (9 M0, 3 M1, 10 M2, 4 M3, 28 M4/M5, 1 M6, 1 M7) between 2007-2009 in Hematology Department of "Sf. Spiridon" Hospital Iasi. We used an extended panel of monoclonal antibodies and we determined the level of expression of cytokines receptors (IL3Ra, IL7R) and chemokines (CXCR4, CKR5). RESULTS: In our study, IL7R expression on AML blasts was significant correlate with low WBC count at diagnosis (p = 0.04) and with multilinear displasia (p = 0.01), high CXCR4 expression was correlate (p = 0.05) with lack of response at first induction therapy and CD123 (IL3Ra) expression was correlate with M4 FAB phenotype. Survival was negative influenced by presence of IL3R on AML blasts, but flt3 mutations, CXCR4, IL7R expression on leukemic cells, other phenotypic aberrancies did not influenced treatment response and survival in our patients population. CONCLUSION: Complete investigation of leukemic cells phenotype extended with cytokines/chemokines receptors at diagnostic is useful for correct characterization of the disease, for discover new prognostic categories and for better identification of minimal residual disease.

Flow cytometry-based quantification of cytokine levels in AML patients plasma and cell culture supernatants.

AIM: Bone marrow stromal cells (BMSCs) have been found to support leukemic cell survival; however, the mechanisms responsible are far from being elucidated yet. The main aim of the current study is to identify particular cytokine/chemokine patterns of acute myeloid leukemia (AML) cells, and, on a longer term, to correlate them with the patient outcome and response to therapy. Therefore, the influence of BMSCs on in vitro modulation of cytokine secretion (IL-1beta, TNF-alpha, IL-10, IFN-gamma, IL-4, IL-5, and IL-2) by AML cells as well as the AML cells supportive capacity of BMSCs-derived soluble factors was investigated. MATERIAL AND METHODS: With this purpose, we used an in vitro experimental model consisting in the evaluation of the effect of BMSC confluent layers-conditioning medium (BMSC-CM) on M4/5 AML cell cultures. RESULTS: Our results show that BMSC-CM from both AML patients and healthy subjects conferred a substantial beneficial effect on AML cells throughout the culture (p=0.0002 and 0.0020 respectively at 24 hours and p=0,0013 and 0,0030 respectively at 72 hours), with a temporary increase in AML cell viability conferred by BM plasma from AML patients. Significant differences were observed with respect to IL1 b secretion which was upregulated in AML cell cultures both after 24 and 72 hours following the addition of AML-BMSC-CM, in contrast to control-BMSC-CM. CONCLUSION: Our results suggest the contribution of BMSCs from AML patients to the generation of particular factors which may be key players involved in the in vivo maintenance of the malignant clone.

[Evaluation of oral injuries in experimental induced diabetes mellitus by analysis of some gingival fluid markers]. / Evaluarea afectarii teritoriilor orale in diabetul indus experimental prin analiza unor markeri in fluidul gingival.

AIM: The objective of this study was to determine the relationship between the activity of the enzyme aspartate aminotransferase (AST) and IL1-beta in gingival crevicular fluid (GCF) on animal model with experimentally induced diabetes mellitus and periodontal disease. MATERIAL AND METHOD: During our study we used 15 Wistar rats, divided into three groups: I--control, II--with experimental model of periodontal disease, III--with experimental model of periodontal disease and diabetes. The sampling of GCF was realized using Whatman no. 1 paper strips introduced in the gingival sulci from mandibular left and right molars. For the determination of AST in GCF we used a spectrophotometric method while gingival fluid IL-1beta determinations were realized through immune enzymatic methods, using an ELISA kit (rlL-1beta). RESULTS: The results displayed 3.47 times increased gingival fluid AST values in the stimulated experimental model (with periodontal alteration) when compared to control values (without periodontal disease), while in diabetes an increase of 6.139 times higher compared to control (without periodontal disease) were recorded. Moreover, the levels of periodontal disorder-induced IL-1beta were 3.54 times higher compared to control (group II--218.490 pg/mL vs group I--61.691 pg/mL), the most significant increase being recorded for the group with diabetes associated to periodontitis (492.129 pg/mL). CONCLUSION: The present study found a high level of agreement between the presence of AST and IL-1beta in GCF in the experimental model of diabetes associated to periodontal disease, elevated when compared with the periodontal disease only model, and both higher when compared to control group.

Characterization of in vitro growth of multiple myeloma cells.

OBJECTIVE: To develop an in vitro culture system for rapid assessment of multiple myeloma (MM) cell growth. METHODS: MM cells lines (MMCLs) L363, U266, and RPMI-8226, and bone marrow (BM)-derived plasma cells (PCs) from MM patients were evaluated for their in vitro growth using various stroma (BMSC, M210-B4, and osteoclasts [OCs]) and cytokine support combinations (combination A: interleukin [IL]-6, vascular endothelial growth factor, insulin-like growth factor-1 vs combination B: A plus hepatocyte growth factor, IL-13 vs combination C: IL-6, insulin-like growth factor -1, stromal-derived growth factor-1, Galectin-1, IL-1alpha). RESULTS: We found a significant effect of stroma, notably affecting growth of L363 cells. Cytokine combination A had the highest growth impact, whereas B and C were of lesser benefit. The contribution of combined cytokines and stroma for MMCL growth was moderate and the viability of MMCLs was best preserved with OCs. One of the most commonly used PC-marker CD138, expressed on all MMCLs on day 0, showed a gradual downmodulation upon all culture conditions, possibly induced as a stroma-triggered phenotypic change, and leading to the ability of MM cells to dedifferentiate into immature, resilient phenotypes. PC-enriched BM samples from 7 of 10 MM patients could be maintained in culture, again profiting from stroma more than cytokines alone. CONCLUSIONS: Our data demonstrate a consistent growth advantage provided by BMSCs on MMCLs and primary MM cells, preserved viability with OCs, and phenotypic and morphologic heterogeneity of primary MM cells during culture. Further identification of key components involved in MM cell growth, coupled with our understanding of drug sensitivity offers the potential to better define the disease pathogenesis and to identify novel therapeutic targets.

[High values of soluble cytokeratin 18 in breast carcinomas may have different meanings]. / Valorile crescute ale citokeratinei 18 serice in neoplasmele mamare pot avea semnificatii diferite.

We have investigated the cellular and serum CK18 in 26 non-treated primary ductal invasive breast carcinomas. The soluble CK18 (TPS) was detected by chemiluminescent assay, and the cellular CK18 and PCNA expression by immunocytochemistry. Flow-cytometry was used to estimate the amount of DNA in malignant cells. There was a significant correlation between soluble CK18 and the pre-menopausal status (p < 0.05), characterized in our group by a PCNA estimated low proliferation index. We have also found a significant correlation between soluble CK18 and the DNA index (p < 0.01). The intracellular CK18 has correlated with the PCNA expression (p < 0.05), while no correlation could be found between cellular and serum CK18. The values of soluble CK18 may offer information about the treatment-induced cell death, if monitored, while isolated measurements should be interpreted cautiously. Elevated levels of serum CK18 in non-treated carcinomas may rather reflect a high tumor turn-over or perhaps a more intensive tumor cell killing.

[The study of two immunological markers in patients with type-1 diabetes and in their first degree relatives]. / Studiul a doi markeri imunologici la pacientii cu diabet de tip 1 si la rudele de gradul I ale acestora.

UNLABELLED: The prediction of diabetes mellitus is mostly based on the existence of plasma markers. The aim of this preliminary study was to determine islet cell antibodies (ICA) and glutamic acid decarboxylase antibodies (GADA) in 28 diabetic children (12 of them having an evolutive disease of 1 year and 16 at the beginning of the diabetes) and to 47 of their first-degree relatives. There have been determined the levels of these two autoantibodies using the ELISA technique. RESULTS: To 17 of the patients with type I diabetes have been found high levels of GADA (60.7%) while 8 cases have positive ICA (28.5%). For the patients whose disease was diagnosed 1 year ago there have been found differences between the patients with and without antibodies regarding the level of the average values of Hb A1c, the daily insulin needs and the remission period. From the tested parents (a total of 25), 7 was GADA positive (28%), 6 had both antibodies present (24%) and one mother was ICA positive (4%). 9 of the brothers and sisters of the diabetic patients had high levels of GADA and 2 had both antibodies present. To the first-degree relatives with autoantibodies must be determined other plasma markers too (IAA, IA-2A) as well as genetic markers (HLA typing). CONCLUSION: The use of plasma markers is recommended as a first step in discovering the relatives with potential risk of developing the disease.

T cell reactivity to Listeria monocytogenes amongst us.

In the last two decades, listeriosis, caused by the intracellular pathogen Listeria monocytogenes, became one of the most concerning food-born infections. Although it had been known before as an infectious disease of limited importance, listeriosis was brought into attention of scientists due to the frequent outbreaks recently reported. Despite the major progress made towards understanding the mechanisms of virulence of L. monocytogenes, our current knowledge into the process of Listeria-associated pathogenesis and virulence is still partial and fragmentary. In this study we demonstrate that T lymphocytes with reactivity to L. monocytogenes are frequently present in healthy individuals (73%), most probably as a consequence of subclinical infections. Host resistance to infection by L. monocytogenes involves a series of interactions between cells of the immune system, of which the antigen presenting cell/T lymphocyte partnership is essential. The ability of memory T cells to respond when exposed to their target antigen is traditionally assessed by measuring uptake of [3H] - thymidine. Our study has been carried out by means of an alternative methodology based on flow-cytometry, an approach which has several advantages on [3H] - thymidine incorporation technique: allows targeted analysis of particular cell types, simultaneous assessment of various cellular markers, and circumvents handling of radioisotopes.

Listeria monocytogenes--host interaction.

Both innate and adaptive immunity against Listeria monocytogenes are essential in circumventing or fighting the disease, although there is no clear delineation of the precise role of either in listeriosis. A consistent amount of in vivo experiments have generated a complex picture over the impact of listerial infection on the hosts, and they are shortly reviewed in this paper.