Cytomegalovirus-induced immunosuppression

Altered microRNA expression after infection with human cytomegalovirus leads to TIMP3 downregulation and increased shedding of metalloprotease substrates, including MICA

Proteolytic shedding of ligands for the NK group 2D (NKG2D) receptor is a strategy used by tumors to modulate immune recognition by NK cells and cytotoxic T cells. A number of metalloproteases, especially those of the A disintegrin and metalloprotease (ADAM) family, can mediate NKG2D ligand cleavage and this process can be modulated by expression of the thiol isomerase ERp5. In this article, we describe that an increased shedding of the NKG2D ligand MICA is observed postinfection with several strains of human CMV due to an enhanced activity of ADAM17 (TNF-α converting enzyme) and matrix metalloprotease 14 caused by a reduction in the expression of the endogenous inhibitor of metalloproteases tissue inhibitors of metalloproteinase 3 (TIMP3). This decrease in TIMP3 expression correlates with increased expression of a cellular miRNA known to target TIMP3, and we also identify a human CMV-encoded microRNA able to modulate TIMP3 expression. These observations characterize a novel viral strategy to influence the shedding of cell-surface molecules involved in immune response modulation. They also provide an explanation for previous reports of increased levels of various ADAM17 substrates in the serum from patients with CMV disease. Consistent with this hypothesis, we detected soluble MICA in serum of transplant recipients with CMV disease. Finally, these data suggest that it might be worthwhile to prospectively study ADAM17 activity in a larger group of patients to assay whether this might be a useful biomarker to identify patients at risk for development of CMV disease.

The human cytomegalovirus UL11 protein interacts with the receptor tyrosine phosphatase CD45, resulting in functional paralysis of T cells

Human cytomegalovirus (CMV) exerts diverse and complex effects on the immune system, not all of which have been attributed to viral genes. Acute CMV infection results in transient restrictions in T cell proliferative ability, which can impair the control of the virus and increase the risk of secondary infections in patients with weakened or immature immune systems. In a search for new immunomodulatory proteins, we investigated the UL11 protein, a member of the CMV RL11 family. This protein family is defined by the RL11 domain, which has homology to immunoglobulin domains and adenoviral immunomodulatory proteins. We show that pUL11 is expressed on the cell surface and induces intercellular interactions with leukocytes. This was demonstrated to be due to the interaction of pUL11 with the receptor tyrosine phosphatase CD45, identified by mass spectrometry analysis of pUL11-associated proteins. CD45 expression is sufficient to mediate the interaction with pUL11 and is required for pUL11 binding to T cells, indicating that pUL11 is a specific CD45 ligand. CD45 has a pivotal function regulating T cell signaling thresholds; in its absence, the Src family kinase Lck is inactive and signaling through the T cell receptor (TCR) is therefore shut off. In the presence of pUL11, several CD45-mediated functions were inhibited. The induction of tyrosine phosphorylation of multiple signaling proteins upon TCR stimulation was reduced and T cell proliferation was impaired. We therefore conclude that pUL11 has immunosuppressive properties, and that disruption of T cell function via inhibition of CD45 is a previously unknown immunomodulatory strategy of CMV.

The human cytomegalovirus (CMV) belongs to a class of viruses that interferes with the immune response of its host. Accordingly, infection with CMV is a severe risk for immunologically immature newborns and immunocompromised patients such as transplant recipients. The mechanisms by which CMV affects the immune system are not completely understood. Here we show that a CMV protein, pUL11, which is expressed on the surface of cells, binds to leukocytes by interacting with the receptor tyrosine phosphatase CD45. In T cells, CD45 is essential for transmission of activating signals received via the T cell receptor (TCR) to downstream effector molecules that ultimately lead to activation and proliferation of these immune cells. Binding of the CMV pUL11 protein to CD45 on T cells prevents signal transduction via the TCR and restricts T cell proliferation. Interestingly, the mechanism by which the activity of CD45 is regulated is a matter of debate and no specific cellular ligand of CD45 has yet been described. The identification of a first viral ligand for CD45 may provide the means to investigate CD45 regulatory mechanisms and also allow the development of therapies to interfere with CMV-mediated immunomodulation.

Human cytomegalovirus (HCMV) infection in osteosarcoma cell line suppresses GM-CSF production by induction of TGF-beta

This study was performed to elucidate the possible mechanism of the disturbance of hemopoiesis by HCMV infection. Saos-2 cells constitutively express mRNA of GM-CSF, and its expression was profoundly decreased by HCMV infection, which required full replication of the virus and was mediated by soluble factors released from the HCMV-infected Saos-2 cells. TGF-beta1 production was statistically and significantly increased from one day after HCMV infection. Expression and production of GM-CSF in Saos-2 cells were restored when a culture supernatant of HCMV-infected Saos-2 cells was reacted with neutralizing anti-TGF-beta antibody. Conclusively, HCMV inhibits GM-CSF expression in Saos-2 cells partly by the increased production of TGF-beta1.

Human cytomegalovirus inhibits differentiation of monocytes into dendritic cells with the consequence of depressed immunological functions

Human cytomegalovirus (HCMV) infections in immunocompromised patients are associated with impaired immunological functions. Blood monocytes, which can differentiate into dendritic cells upon cytokine stimulation, play a central role in adequate immune reactivity and are believed to carry latent HCMV. We demonstrate here that HCMV infection of monocytes results in a block in the cytokine-induced differentiation of monocytes into functionally active CD1a-positive dendritic cells, which exhibited severely depressed immunological functions in vitro. The HCMV-infected cells exhibited a significantly reduced ability to endocytose fluorescein isothiocyanate-labeled dextran particles as well as a more than 90% reduced ability to migrate in response to the chemoattractant factors RANTES, MIP-1alpha, and MIP-3beta. Interestingly, HCMV-infected cells expressed high levels of the costimulatory molecule CD86, in contrast to the low levels of expression that was observed on uninfected monocytes and uninfected immature dendritic cells. Furthermore, HCMV-infected CD1a-negative cells were unable to induce a T-cell response. Thus, these observations suggest that HCMV infection of monocytes in vitro blocks cytokine-induced dendritic cell differentiation, and since dendritic cells play a central role in initiating immune responses, these findings suggest a powerful tactic to avoid immune recognition and to blunt the immune response at early phases of infection.

Infection of dendritic cells by murine cytomegalovirus induces functional paralysis

Cytomegalovirus (CMV), measles and HIV are the main human pathogens known to induce immunosuppression. Unlike measles and HIV, and despite the availability of a well studied animal model, little is known about the mechanisms that control CMV-induced immunosuppression. We hypothesized that dendritic cells (DCs), which are crucial in generating and maintaining immune responses, represent a target for CMV and that the transient, but profound, immunosuppression that accompanies CMV infection results from viral interference with DC functions. Here we show that DCs were permissive to murine CMV infection. In addition, DC infection prevented delivery of the signals required for T cell activation. Thus, CMV-mediated impairment of DC function may be crucial for virally induced immunosuppression and interleukin 2 is implicated as a key factor.

Cytomegalovirus (CMV) infection in AIDS patients is associated with a CD3 receptor-mediated T cell hyporesponsiveness

HIV+ individuals with human CMV (HCMV) reactivation have a CD3 receptor-mediated T cell hyporesponsiveness when compared with CD4-matched HIV+ and HCMV- control groups. The impairment of proliferation was not reversed by exogenous IL-2. A typical increase in NFkappaB expression was observed following cross-linking of the CD3 receptor, but did not lead to increased CD25 cell surface expression or cell proliferation. The HCMV-induced non-responsiveness was not observed when cells were stimulated with phorbol esters. Lymphocytes cultured with media collected from cell cultures infected with HCMV showed a dose-dependent inhibition in the total T cell population even though cells staining dually for CD8/57 increased in number. The altered growth factor requirements of CD8/57+ cells may therefore account for their presence in AIDS and patients following bone marrow transplantation.

The effect of human cytomegalovirus on selected functions of peripheral blood monocytes

The effect of in vitro infection of human cytomegalovirus (HCMV) on various monocyte functions relevant to antimicrobial defence mechanisms has been investigated: the phagocytic activity of monocytes, the release of lysozyme and intracellular concentration of acid phosphatase, and the release of the cytokines interleukin-1 (IL-1), IL-6, and tumour necrosis factor-alpha (TNF-alpha). HCMV significantly inhibited the release of lysozyme and intracellular concentration of acid phosphatase. Regarding the phagocytic activity and the release of cytokines, there was considerable variation in the HCMV effect among the different blood donors tested. There was no clear tendency in the observed results; both stimulation and inhibition were seen. The HCMV-specific pp65 was detected in the nucleus of about 1% of the monocytes 3 h after infection and HCMV-specific IE antigens were found in about 0.1% of the monocytes 2 days postinfection. No E- or L-gene expression was observed and no infectious virus was produced in the monocytes. Our results indicate that HCMV infection may influence monocyte functions in spite of no productive infection of these cells.

Selective impairment of T lymphocyte activation through the T cell receptor/CD3 complex after cytomegalovirus infection

Cytomegalovirus (CMV) infection is reported to cause transient immunosuppression in man. In this study we have analysed the effect of CMV on T lymphocyte function in 29 children diagnosed for acute CMV infection. Peripheral blood mononuclear cells (PBMC) obtained from the patients showed a significant specific impairment in their proliferative response to enterotoxins A and C1, to concanavalin A and to the anti-CD3 MoAb OKT3. The impaired responses were corrected with exogenous IL-2. In contrast, stimulation using phytohaemagglutinin, as well as activation signals delivered through the surface molecules CD26 or CD28, elicited normal proliferative responses in CMV PBMC. The results indicate that the T cell anergy associated with CMV infection is restricted to the T cell receptor/CD3 activation pathway.

Aspergillus fumigatus fungaemia and myocarditis in a patient with acquired immunodeficiency syndrome

Necrotizing myocarditis due to Aspergillus fumigatus was a contributory cause of death in a patient with acquired immunodeficiency syndrome and non-Hodgkin lymphoblastic malignant lymphoma of the Burkitt type. A transient remission of the lymphoma had been obtained by cytostatic treatment. A. fumigatus was isolated from blood two weeks before death, but myocarditis was not diagnosed until autopsy.

Proliferative response of mononuclear cells from HIV-infected patients to B-cell mitogens: effects of lymphocyte subset frequency, T-cell defects and prostaglandins

Proliferative responses of mononuclear cells from patients seropositive for human immunodeficiency virus to B-cell mitogens are severely depressed compared with those of controls. The role of several immunoregulatory phenomena was analyzed. Experimental results show that addition of exogenous lymphokines to cultures increases responses to anti-mu and SAC. Addition of indomethacin to cultures greatly increases the SAC response and causes a smaller increase in the pokeweed mitogen (PWM) response. When both exogenous lymphokines and indomethacin are present in cultures, responses of patients' cells to all three mitogens are positively correlated with the percentage of CD4+ T cells and negatively correlated with the percentage of CD8+ T cells. Responses to anti-mu and SAC are also positively correlated with the percentage of B cells in these cultures. On the basis of these correlations between B-cell responses and lymphocyte subset frequency, patients' B-cell responses can be mathematically corrected to estimate the responsiveness of the B cells in the presence of normal numbers of CD4+ and CD8+ cells. These corrected responses for all three mitogens are virtually identical to control responses. Furthermore, responses of enriched B-cell populations from HIV+ subjects and normal controls to SAC were not significantly different when assays were performed in the presence of indomethacin and exogenous lymphokines. These results suggest that B cells from HIV+ patients are inherently normal in their responsiveness to B-cell mitogens. The depressed function is imposed upon them as a result of the abnormal frequency of lymphocyte subsets in the blood, by increased prostaglandin production, and deficient lymphokine production.

Activation of feline immunodeficiency virus long terminal repeat by feline herpesvirus type 1

By transfection of a recombinant plasmid containing the feline immunodeficiency virus (FIV) long terminal repeat (LTR) linked to the chloramphenicol acetyltransferase (CAT) gene followed by infection of feline herpesvirus type 1 (FHV-1) into Crandell feline kidney cells and Felis catus whole fetus 4 cells, enhancement of CAT activity was demonstrated. Furthermore, individual feline T-lymphocytes were productively co-infected with both FIV and FHV-1 in vitro as determined by two-color immunofluorescence and electron microscopy analyses. These results revealed the transactivation of the FIV LTR by FHV-1 and the dual infection of T-lymphocytes with both viruses. The possibility that FHV-1 might be a cofactor which plays a role in the pathogenesis of FIV infection is discussed.

Increased monokines in cytomegalovirus infected myelomonocytic cell cultures

In an investigation of the role of monokines in CMV associated immunosuppression we document modulation of both TNF and IL-1 beta in CMV infected THP-1 cells. CMV infected cultures released almost two-fold more IL-1 beta protein and contained significantly higher IL-1 beta mRNA levels than uninfected cultures for 72-96 h after induction. In both CMV infected and uninfected cultures, significant amounts of IL-1 beta protein were not detected until 24 h post induction, while maximum amounts of TNF were detected in culture supernatants by 3 h post induction, suggesting that TNF may play a role in IL-1 beta induction. TNF levels subsequently declined but in infected cultures remained over 2.5-fold higher than controls through 96 h. The CMV alteration in the kinetics and extent of IL-1 beta release must be indirectly mediated by CMV since only 1% of THP-1 cells were infected. Most infected cells expressed CMV immediate early proteins but did not overexpress IL-1. We speculate that CMV infected cells release excess TNF or other stimulatory factors which increase IL-1 beta synthesis. Since IL-1 beta is increased, the decreased IL-1 'activity' described by others as an explanation in part for the immunosuppressive effects of infection may actually reflect alterations of IL-1 inhibitor levels during CMV infection.

Immune complex assays: diagnostic and clinical application

The presence of circulating immune complexes have been described in many different human disease states but the significance of their presence has always been a subject for debate. Improvements in the methods of detecting immune complexes have demonstrated a wide degree of heterogeneity, which accounts for the difficulty in obtaining accurate and reproducible measurements, even in the same individual. Techniques for isolating individual complexes, characterizing their pathophysiological properties, and biochemically analyzing the nature of the complexed antigen are now being used to provide data that is helping to clarify the role of immune complexes in the pathogenesis of disease. In addition, such studies are also providing data which is proving that immune complexes have a potential role in immune regulation.

Cytomegalovirus infection of peripheral blood mononuclear cells: effects on interleukin-1 and -2 production and responsiveness

Cytomegalovirus suppresses the proliferative response of peripheral blood mononuclear cells to phytohemagglutinin. In these experiments, we identified which mononuclear cell subpopulation might be responsible for the suppression. We found that prior infection of either lymphocytes or monocytes followed by reconstitution with monocytes or lymphocytes, respectively, would abrogate the proliferative response in a subsequent culture with phytohemagglutinin. Infection of either cell type also reduced both the production of interleukin-1 (IL-1) and IL-2 and the proliferative response to exogenously supplied IL-1 or IL-2. We did not find evidence for an IL-2 antagonist. These experiments suggest that cytomegalovirus causes a metabolic derangement in lymphocytes and monocytes and impairs their ability both to produce and to respond to physiological mediators of the immune response.

Cytomegalovirus

Cytomegalovirus (CMV) has emerged as an important cause of human illness. Infection with this common virus can result in asymptomatic infection, an acute “mononucleosis-like” illness, or congenital disease. It is capable of persisting in a latent state and reactivating at a later date. It can be transmitted by blood transfusion, organ transplantation, oral or genital contact, intrauterine infection, perinatal infection and perhaps casually by children in day care centers.

Historically, the first reports described “protozoan-like” cells in the organs of a fetus and a stillborn in 1904. In 1932, Farber reported the presence of inclusions in the nucleus and cytoplasm of cells in infants dying of various causes and coined the term cytomegalic inclusion disease. The urine was initially cultured in 1953 by Smith, and the subsequent development of serologic methods of diagnosis made its broad spectrum of disease more fully appreciated.

Herpes simplex virus type-1 can reactivate transcription of latent human immunodeficiency virus

The human immunodeficiency virus, HIV (formerly T-cell lymphotropic virus type III, HTLV-III or lymphadenopathy-associated virus, LAV) is the primary cause of AIDS (acquired immune deficiency syndrome). Patients with AIDS have profound immunosuppression as a result of almost complete absence of the OKT4+ cell population and are predisposed to a number of opportunistic infections as well as to certain malignant diseases such as Kaposi's sarcoma and B-cell tumours. The majority of the opportunistic infections observed in AIDS patients are from the herpesvirus group and these are frequently the cause of death in AIDS patients. We have therefore investigated the effect of herpes virus infection on the expression of HIV and we provide evidence that herpes simplex virus type I (HSV-I) can reactivate transcription of latent HIV. In OKT4+ human T-cells HIV replicates to high virus titres, resulting in high level expression of viral RNA. This high level of expression has been attributed to virus-associated trans-acting factors that increase gene expression, directed by the HIV long terminal repeats (LTR), post-transcriptionally. In our studies we have tested whether transcription directed by the LTR of HIV is stimulated by HSV-I.

Impaired production of alpha and gamma interferon in asymptomatic homosexual males

In vitro production of alpha interferon and gamma interferon was examined in cell cultures from 90 asymptomatic homosexual males and 19 healthy heterosexual male controls. The production of alpha and gamma interferon was significantly suppressed in homosexuals as compared to that in heterosexual controls (p less than 0.005 and p less than 0.001, respectively). Forty-one of the homosexuals produced less gamma interferon than any of the heterosexual controls. Antibodies against the human immune system virus (HIV) were found in eight homosexuals, who produced significantly less alpha and gamma interferon than did the HIV-seronegative homosexuals (p less than 0.02). Neither carriage of Entamoeba histolytica or Giardia lamblia nor serological evidence of infection with cytomegalovirus, Epstein-Barr virus or hepatitis B virus was associated with a significantly lower production of interferon than that found in homosexual males seronegative for these infections. No correlation was found between number of partners or practice of passive anal intercourse and production of interferons in homosexual men. It is concluded that the significantly lower production of both alpha and gamma interferon in asymptomatic homosexual males may play an important role in susceptibility to viruses, including HIV.

Intravenous immunoglobulins: pharmacological aspects and therapeutic use

The requirements for a present-day IVIG preparation are outlined. These are mainly: fully preserved activities of the recognition and effector functions of the IgG molecule, a normal subclass distribution, and a normal half-life after infusion. The therapeutic uses of IVIG preparations are discussed as follows: Antibody substitution in cases of generalized or partial antibody deficiency in immune-compromised patients. These include the following diseases: hypogammaglobulinemia (congenital and acquired, including the neonates); drug-induced and viral immunosuppression. Antibody substitution in cases of selective antibody deficiency in otherwise immune-competent patients. These include acute cases of consumptive antibody deficiencies of the Jarisch-Herxheimer reaction type; in particular, chronic inflammations which apparently involve ineffective immune responses in which the organism is unable to build up sufficient amounts of antibodies with the required partial specificity, which is indispensable for overcoming the disease. Modulation of the immune system by Ig-Ig interactions (mainly idiotype-anti-idiotype interactions) and Ig-Fc-receptor interactions, as it is known from the RES blockade during IVIG treatment of idiopathic thrombocytopenic purpura.