Structure, Metabolism, and Functions of Peripheral Blood Lymphocytes during Long-Term Persistence of Epstein-Barr Virus

Study of surface architectonics, blast transformation potential, and cytochemical activity of peripheral blood lymphocytes from children infected with Epstein-Barr virus revealed imbalance between structural, metabolic, and functional state of lymphocytes. This imbalance persists in delayed period after infection and determines long-term viral persistence in the macroorganism.     

CD44 stimulation down-regulates Fas expression and Fas-mediated apoptosis of lung cancer cells

Cytotoxic T lymphocytes (CTL) play a major role in the rejection of tumor cells, but tumor rejection does not always occur in vivo, indicating that defects in anti-tumor immune responses may be common. We here document a novel function for CD44--using lung cancer cells, we showed that stimulation of CD44 reduced Fas expression and Fas-mediated apoptosis: (i) lung cancer cells expressed high levels of CD44; (ii) engagement of CD44 on the cells by a specific antibody or fragmented hyaluronan reduced Fas expression; (iii) CD44 cross-linking reduced Fas-mediated apoptosis; (iv) stimulation of CD44 on lung cancer cells decreased IFN-gamma production by autologous CTL; and (v) CD44 stimulation prevented killing of lung cancer cells by autologous CTL. Based on these findings, we postulate a new concept--that interaction of CD44 on lung cancer cells with fragments of extracellular hyaluronan present in the surrounding extracellular matrix reduces Fas expression as well as Fas-mediated apoptosis of cancer cells. This leads to reduced susceptibility of the cells to CTL-mediated cytotoxicity through the Fas-Fas ligand pathway.     

Absence of Epstein-Barr virus-specific, HLA class II-restricted CD4+ cytotoxic T lymphocytes in infectious mononucleosis.

Cytotoxic T lymphocytes (CTL) with the CD4+ phenotype that recognize major histocompatibility complex (MHC) class II antigens are detectable very frequently in cultures of human alloreactive or virus-specific T cells. The significance of these CD4+ CTL for an immune reaction in vivo is not clear. Since Epstein-Barr virus (EBV) transformed B cells express HLA-class I and class II antigens equally well both CD8+ and CD4+ CTL should be stimulated during an acute EBV infection. We analysed the MHC specificity and the phenotype of EBV-specific CTL from patients with infectious mononucleosis (IM). When tested directly without any previous culture, T cells from patients in the acute phase of IM showed specific MHC-restricted cytotoxicity against the autologous B cell line. Addition of a HLA class I specific monoclonal antibody (MoAb) but not of a HLA class II specific MoAb resulted in a complete blocking of the lytic activity. Cell sorting revealed that the entire cytotoxic activity was present in the CD8+ fraction whereas no specific CTL were detectable in the CD4+ fraction. The absence of cytotoxicity in CD4+ cells was not due to a lack of activation of these cells since both CD8+ and CD4+ cells were activated in situ, showing spontaneous growth in interleukin-2 (IL-2) and expressing the activation marker TP103. Frequency estimation revealed that 1/300-1/600 CD8+ but only 1/2000-1/4000 CD4+ T cells gave rise to a specific CTL colony after 10 days. If CD4+ colonies were tested repeatedly for cytotoxicity we found that CD4+ CTL acquired their cytotoxicity during in vitro culture. In addition, we isolated EBV-specific CD4+ T cell clones able to lyse their stimulator cells in the presence but not in the absence of lectin, even after a long period of culture. Taken together our results show that cytotoxicity mediated by CD4+ T cells does not play a role in an anti-viral immune response.     

CD4+/CD8+ ratio of liver-derived lymphocytes is related to viraemia and not to hepatitis C virus genotypes in chronic hepatitis C.

The pathogenic mechanisms that lead to chronic hepatitis C are unknown. As hepatitis C virus (HCV) has been shown to induce T cell response, we assessed whether a particular T lymphocyte subset could be preferentially detected in the liver of patients with chronic hepatitis C in relation to viraemia or HCV genotypes. The immunophenotypes of liver-derived lymphocytes were analysed in 26 patients by flow cytometry and immunohistochemistry. Viraemia was quantified by branched DNA assay. Using this assay, HCV RNA was not detectable in six patients. HCV RNA was detected in 20 patients, and titres ranged from 8 to 137 x 10(6) Eq/ml. Genotyping was performed using a line probe assay. Type 1a, 1b, 2a, 3a and 4a were found to infect 2, 10, 2, 7 and 3 patients, respectively. The CD4+/CD8+ ratio of liver-derived lymphocytes was significantly higher (P < 0.01) in patients with detectable viraemia than in patients without detectable viraemia. In contrast, neither the percentage of gamma/delta T lymphocytes nor that of CD2+CD57+ cells was different in the groups. When comparing the CD4+/CD8+ ratio, the percentage of gamma/delta T lymphocytes or CD2+CD57+ cells according to genotype, the differences were not significant. These results suggest that the CD4+/CD8+ ratio of liver-derived lymphocytes is related to viraemia but not to HCV genotypes in patients with chronic hepatitis C, and that T lymphocytes may be involved in the pathogenesis of liver lesions in chronic hepatitis C.     

Coxsackievirus B3 replication and persistence in intestinal cells from mice infected orally and in the human CaCo-2 cell line

Although the transmission of coxsackievirus B3 occurs mainly via the oral route, little is known about the primary replication and persistence of this agent in the intestine. To address this question, BALB/c mice were inoculated by gavage with coxsackievirus B3, Nancy strain. The mice were killed from 1 hr to 90 days after infection. The viral markers were detected in the small intestine using RT-PCR, cell culture and detection of VP1 protein. Coxsackievirus B3 was detected positive by the three methods from hr 2 to day 45 after infection. By using monoclonal antibodies directed towards VP1, CD40 and CD26, the virus was shown to be present in the lymphocytes of the mucosa as soon as 2 hr after infection; in contrast, no virus was detected in the epithelial cells lining the intestinal lumen. Further experiments were performed to evaluate the capacity of coxsackievirus B3 to establish a persistent infection in two intestinal cell lines. In contrast to HT29 cells, the CaCo-2 cells were shown to develop a persistent infection for up to 20 passages, as demonstrated by the detection of viral RNA and VP1 protein. This study provides further evidence that, after infection by the oral route, the viral particles are concentrated in the lymphocytes of the mucosal layer. In addition, the results suggest that coxsackievirus B3 is capable of establishing a persistent infection in the small intestine that may act as a reservoir of viral particles for the delayed spread of the virus to other target organs.     

Increased expression of intercellular adhesion molecule-1 (ICAM-1) in a murine model of pulmonary eosinophilia and high IgE level.

T lymphocytes and eosinophils are probably involved in the pathogenesis of allergic bronchopulmonary aspergillosis (ABPA), a disease characterized by pulmonary eosinophilia and high serum and lavage IgE levels. We recently developed a murine model of ABPA. To investigate the mechanisms of T lymphocyte and eosinophil recruitment to the lung in this disease, we examined the expression of ICAM-1 in the lung tissue of mouse challenged with Aspergillus fumigatus (Af) antigen. C57B1/6 mice were intranasally exposed to Af (Af group) or saline (control group) three times a week for 1, 2 or 3 weeks. On days 4, 7, 14 and 21, mice were killed and lung tissue was fixed in acetone and embedded in glycol methacrylate. Serial 2-microns sections were stained with chromotrope 2R and MoAbs against ICAM-1, CD11a/CD18 (LFA-1) and CD3. Af-challenged mice presented significant increases in eosinophil, T lymphocyte and LFA-1-positive cell count and up-regulated expression of ICAM-1 in the lung tissue at all the time points examined. ICAM-1 expression intensity correlated with the number of T lymphocytes (r = 0.59, P < 0.01), LFA-1-positive cells (r = 0.68, P < 0.001), but not of eosinophils (r = -0.24, P > 0.05). These findings suggest that up-regulation of ICAM-1 expression is involved in the inflammatory process of this murine model of ABPA, and that this up-regulation may be more relevant to the the T lymphocyte accumulation in the lung.     

Assessment of thymic output in common variable immunodeficiency patients by evaluation of T cell receptor excision circles

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by repeated infections and hypogammaglobulinaemia. Additionally, T-cell abnormalities including lymphopenia, decreased proliferation to mitogens and antigens, and the reduced production and expression of cytokines, have also been observed. In this study we have investigated the expression of naive, memory and activation markers in T-cell subpopulations in 17 CVID patients in comparison to age-matched normal controls. The numbers of CD4+ T cells, including CD45RA+CD62L+ and, to a lesser extent, CD45RA-CD62L+/RA+CD62L- were significantly reduced in patients, whereas CD8+ T cells were within normal range. In contrast, HLA-DR+ cells were increased both in CD4+ and CD8+ T cells. To assess the thymic output, we analysed the presence of T-cell receptor excision circles (TRECs) in CD4+ and CD8+ T cells by quantitative PCR. TRECs were decreased significantly in patients and the rate of TREC loss was higher with increasing age. TRECs correlated with naive CD4+ T cells, whereas there was an inverse relationship between TRECs and CD8+HLA-DR+ and CD8+CD45RA-CD62L+/RA+CD62L- T cells. Our results suggest the presence of a defect in the naive T cell compartment with origin at the thymic level in CVID, and indicate that TREC may be a useful marker to monitor thymic function in this primary immunodeficiency.     

Specific and non-specific components in the triggering of proliferative and cytotoxic responses of T lymphocytes with different cell density

We hve analyzed the functional behavior of lymphocyte subsets separated on the basis of cell density. Low and high density subpopulations were cultured in FCS, alone or with allogeneic irradiated PBL, and then examined for proliferation and cytotoxic activity against autologous (responder) and allogeneic (stimulator) PHA-induced blasts, K562 and Daudi. In the high density subset proliferation and generation of anti-K562 and anti-Daudi effects were induced by FCS and to higher extent by allospecific stimulation. Exposure to alloantigens induced allospecific cytotoxicity. Autologous PHA blasts were not affected. The results with the low density subset differed. Independently of the type of stimulus imposed, the low density fraction showed little if any proliferation, but its cytotoxic activity was stronger against all targets tested. In some of the experiments, anti-alloblast cytotoxicity was generated in the control cultures. Thus, polyclonal activation induced by FCS triggered in this fraction allospecific cytotoxicity. In this subset, the effect against allogeneic PHA blasts comprised a specific and a non-specific component because autologous PHA blasts were also lysed. Limiting dilution analysis involving allostimulation showed higher frequency of cytotoxic precursors in the low density subset. Split minicultures were tested for lysis of auto- and allogeneic blasts. Alloreactive cultures that did not lyse the autologous target were more frequent in the cultures initiated with the high density cells. There was no conclusive evidence for the existence of autoreactive cultures that did not lyse the allogeneic blasts.