Replication or inactivation of different viruses by human lymphocyte preparations

Diverse and Unexpected Roles of Human Monocytes/Macrophages in the Immune Response to Influenza Virus

Human monocytes/macrophages play a central role in the immune response and defense of the host from influenza virus infection. They classically act as antigen-presenting cells for lymphocytes in the context of an immune cell cluster. In that setting, however, monocytes/macrophages exhibit additional, unexpected, roles. They are required for influenza virus infection of the lymphocytes in the cluster, and they are responsible for lymphocyte apoptosis via their synthesis and expression of the viral neuraminidase. Surprisingly, human alveolar macrophages, expected to be among the first cells to encounter the virus, are not susceptible to direct infection by a human influenza virus but can be infected when the virus is complexed with an antibody. Such monocyte/macrophage responses to influenza virus challenge should be considered part of a very complex but quite effective defense, since the common outcome is recovery of the host with development of immunity to the challenging strain of virus.

Influenza Virus Infection of Human Lymphocytes Occurs in the Immune Cell Cluster of the Developing Antiviral Response

Monocytes-macrophages and lymphocytes are recruited to the respiratory tract in response to influenza virus challenge and are exposed to the virus during the establishment of immune defenses. The susceptibility of human lymphocytes to infection was assessed. The presence of monocytes-macrophages was required to attain infection of both resting and proliferating lymphocytes. Lymphocyte infection occurred in the context of immune cell clusters and was blocked by the addition of anti-intercellular adhesion molecule-1 (ICAM-1) antibody to prevent cell clustering. Both peripheral blood-derived and bronchoalveolar lymphocytes were susceptible to infection. Both CD4⁺ and CD8⁺ T lymphocytes were susceptible to influenza virus infection, and the infected CD4⁺ and CD8⁺ lymphocytes served as infectious foci for other nonpermissive or even virus-permissive cells. These data show that monocytes-macrophages and both CD4⁺ and CD8⁺ lymphocytes can become infected during the course of an immune response to influenza virus challenge. The described leukocyte interactions during infection may play an important role in the development of effective anti-influenza responses.

Viruses within the Flaviviridae decrease CD4 expression and inhibit HIV replication in human CD4+ cells

Viral infections alter host cell homeostasis and this may lead to immune evasion and/or interfere with the replication of other microbes in coinfected hosts. Two flaviviruses are associated with a reduction in HIV replication or improved survival in HIV-infected people (dengue virus (DV) and GB virus type C (GBV-C)). GBV-C infection and expression of the GBV-C nonstructural protein 5A (NS5A) and the DV NS5 protein in CD4(+) T cells inhibit HIV replication in vitro. To determine whether the inhibitory effect on HIV replication is conserved among other flaviviruses and to characterize mechanism(s) of HIV inhibition, the NS5 proteins of GBV-C, DV, hepatitis C virus, West Nile virus, and yellow fever virus (YFV; vaccine strain 17D) were expressed in CD4(+) T cells. All NS5 proteins inhibited HIV replication. This correlated with decreased steady-state CD4 mRNA levels and reduced cell surface CD4 protein expression. Infection of CD4(+) T cells and macrophages with YFV (17D vaccine strain) also inhibited HIV replication and decreased CD4 gene expression. In contrast, mumps virus was not inhibited by the expression of flavivirus NS5 protein or by YFV infection, and mumps infection did not alter CD4 mRNA or protein levels. In summary, CD4 gene expression is decreased by all human flavivirus NS5 proteins studied. CD4 regulation by flaviviruses may interfere with innate and adaptive immunity and contribute to in vitro HIV replication inhibition. Characterization of the mechanisms by which flaviviruses regulate CD4 expression may lead to novel therapeutic strategies for HIV and immunological diseases.

Viremia in hospitalized children with enterovirus infections

In a prospective study during the summer and fall of 1982, enterovirus was isolated from 48 hospitalized children; in 29 (60%) enterovirus was isolated from CSF or blood, and in 19 (40%) only a presumptive diagnosis was established. Blood was positive in 21 (44%) and was the only positive specimen in two children. A presumptive diagnosis was provided within 4 days of admission in 38 (80%) and within 48 hours in 19 (40%) of the children from whom enterovirus was isolated. Viremia was most often detected in febrile infants younger than 3 months of age with a clinical picture simulating bacterial sepsis. The presence of viremia was inversely related to the presence of CSF pleocytosis and to virus isolation from CSF. The diagnosis of diseases caused by enterovirus is more accurate when blood culture is added to CSF stool and throat cultures.

The isolation of enteroviruses from blood: a comparison of four processing methods

Blood from 28 children hospitalized with symptomatic enterovirus infections was processed by four different methods in an effort to define optimum conditions for detecting viremia. Enteroviremia was demonstrated in 11/28 children. Virus was isolated by method 1 (serum) in 7/11 children and by method 2 (mononuclear leukocytes) in 9/11, but in only 3/10 and 3/11 children by methods 3 and 4 (granulocytes and plasma-mixed leukocytes, respectively). In four children, the only blood isolate was from mononuclear leukocytes, and in two, serum was the only positive blood preparation. This suggests that viremia can be often detected in hospitalized children with enterovirus disease and shows that the methods used for processing blood may significantly influence the isolation rate.

Different effects of influenza virus, respiratory syncytial virus, and Sendai virus on human lymphocytes and macrophages

Influenza virus, respiratory syncytial virus, and Sendai virus depress human cell-mediated immune responses, such as mitogen-induced lymphocyte transformation, but differ in their ability to induce other immune defense mechanisms, such as interferon production. Exposure to the different viruses resulted in depressed transformation responses to the mitogen phytohemagglutinin by affecting the function of lymphocytes, or macrophages, or both cell types.

Interaction between 6/94 virus, a parainfluenza type 1 strain, and human leukocytes

6/94 virus, a parainfluenza type 1 virus recovered by lysolecithin fusion of multiple sclerosis brain cell cultures with CV-1 cells, replicated in monocyte macrophages and lymphocytes from normal human donors and from a patient with multiple sclerosis. In macrophage cultures, hemadsorption-positive cells and high levels of infectious virus became apparent within 24 to 48 h after infection, persisted for 6 days, and then began to decrease. Phytohemagglutinin-stimulated macrophages yielded similar titers of virus, but the levels were maintained for a longer period of time. Macrophage-produced virus appeared to be infectious for other macrophages in the same culture. Both unstimulated and phytohemagglutinin-stimulated lymphocytes also supported virus replication. Significantly higher titers were produced in the stimulated cultures, T cell-enriched populations producing more virus than unseparated populations whether stimulated or unstimulated. The presence or absence of antibodies to the virus in the donors did not appear to influence the levels of virus obtained in any of the leukocyte cultures. However, an increase in blastic forms after 6/94 virus infection was noted in lymphocytes from donors with antibodies as revealed morphologically and by increased incorporations of tritiated thymidine. Furthermore, 6/94 virus-infected lymphocytes, unlike Sendai virus-infected lymphocytes, were able to respond well to mitogenic stimulation by phytohemagglutinin.

ECHOvirus 33 replication in human peripheral white blood cells

ECHOvirus 33 isolated from the cerebrospinal fluid of a patient with agammaglobulinemia was shown to replicate in vitro in peripheral leukocyte suspensions from a normal antibody negative donor. Replication was demonstrated by use of sequential dilution experiments. Washed glass adherent mononuclear cell cultures from a normal antibody negative donor were also capable of supporting ECHOvirus 33 replication in vitro. Leukocyte suspensions from the infected agammaglobulinemic patient extinguished detectable infectious virus in vitro.

Comparison of replication of adenovirus type 2 and type 4 in human lymphocyte cultures

Adenovirus type 2 was capable of replicating in purified lymphocyte cultures from human adenoid specimens. Phytohemagglutinin stimulation enhanced the replication of virus. Viral titers of 103 to 104 50% tissue culture infective doses per ml were reached after 4 to 8 days. Only 1 to 3 per 106 cells were found to produce virus. In contrast, there was no evidence that lymphocyte cultures could support the replication of adenovirus type 4. The life span of cultures infected with type 2 or 4 was not reduced. The possibility that lymphocytes infected with virus play a role in initiating natural, persisting adenovirus infections of human adenoids is discussed.

Influenza: response of T-cell lymphopenia to thymosin

Eighteen volunteers in tow study groups were inoculated with influenza A (H3N2) and their peripheral blood T, B and null cells enumerated at subsequent intervals. Infection with wild-type virus or with a live, attenuated virus vaccine markedly reduced the proportion and absolute number of T-cell rosettes 24 hours after inoculation. T-Cell depression preceded the onset of clinical illness in symptomatic subjects, continued during illness, and returned to normal with recovery. T-cell lymphopenia was most pronounced in volunteers infected with wild-type virus and was accompanied by an increase in null cells. Lymphocytes from six wild-virus recipients with T-cell leukopenia were incubated in vitro with a calfthymus extract (thymosin), significantly increasing the percentage of T rosettes in all six subjects (P less than 0.0001). These data indicate that influenza is accompanied by pronounced quantitative and functional changes in T cells.