Measles virus-induced changes in leukocyte function antigen 1 expression and leukocyte aggregation: possible role in measles virus pathogenesis

Hypothermia attenuates beta1 integrin expression on extravasated neutrophils in an animal model of meningitis

Brain injury in meningitis occurs in part as a consequence of leukocyte migration and activation. Leukocyte integrins are pivotal in the inflammatory response by mediating adhesion to vascular endothelium and extracellular matrix proteins. We have demonstrated that moderate hypothermia early in the course of meningitis decreases leukocyte sequestration within the brain parenchyma. This study examines whether hypothermia alters neutrophil integrin expression in a rabbit model of bacterial meningitis. Prior to the induction of meningitis, peripheral blood samples were obtained and the neutrophils isolated. Sixteen hours after inducing group B streptococcal meningitis, animals were treated with antibiotics, i.v. fluids, and mechanically ventilated. Animals were randomized to hypothermia (32-33 degrees C) or normothermia conditions. After 10 hours of hypothermia or normothermia, neutrophils were isolated from the blood and cerebral spinal fluid (CSF), stained for beta1 and beta2 integrins, and analyzed using flow cytometry. Cerebral spinal fluid neutrophil beta1 integrin expression was significantly decreased in hypothermic animals. Beta-1 integrins can assume a higher affinity or "activated" state following inflammatory stimulation. Expression of "activated" beta1 integrins was also significantly decreased in hypothermic animals. Beta2 CSF neutrophil integrin expression was decreased in hypothermic animals, but failed to reach significance. These data suggest hypothermia may attenuate extravasated leukocyte expression of both total and "activated" beta1 integrins.

Measles virus infection causes transient depletion of activated T cells from peripheral circulation

BACKGROUND

Natural measles virus infection as well as vaccination with attenuated measles virus induce temporary immunosuppression, which is responsible for part of the morbidity and mortality associated with measles. The underlying molecular mechanisms are not known. Recently, in vitro studies have revealed a marked increase of LFA-1 expression of lymphocytes in the presence of infectious measles virus.

OBJECTIVES

In order to further investigate immune dysfunction in measles we analyzed the expression of leukocyte function-associated antigen 1 (LFA-1) on ex vivo derived circulating human T cells.

STUDY DESIGN

Expression of LFA-1 was measured by flow cytometry using monoclonal antibodies directed against CD11a and CD18. LFA-1 expression was followed in the course of infection in four adult seronegative vaccinees and in four patients with natural measles.

RESULTS

There was a remarkable loss of LFA-1-bright cells during natural measles and after measles vaccination. The number of LFA-1-bright cells reached a minimum on day 7-14 after vaccination, and at the onset of rash during natural measles infection, and approached normal levels within 3-5 weeks.

CONCLUSION

It is suggested that measles virus infection interferes with lymphocyte trafficking and reallocation. Disruption of recirculation and random homing of lymphocytes might contribute to the immunosuppression, which is characteristic for measles virus infection.

Strain-specific differences in LFA-1 induction on measles virus-infected monocytes and adhesion and viral transmission to endothelial cells

Measles virus (MV) infection of monocytes induces leukocyte function-associated antigen-1 (LFA-1), an integrin that mediates intercellular adhesion to the endothelium. Thus, an increase in LFA-1 expression could lead to enhanced monocyte adherence and virus dissemination to endothelial cells (ECs) and potentially be an important means of distinction between MV strains. We identified both vaccine and wild-type strains that induced LFA-1 and others that failed to induce. Although adhesion of MV-infected monocytes and viral transmission to ECs was demonstrated, strain-specific differences were not correlated with LFA-1 induction. MV infection of ECs was dramatically reduced in the absence of cell contact, suggesting virus dissemination by cell-cell transmission.

Interaction of measles virus glycoproteins with the surface of uninfected peripheral blood lymphocytes induces immunosuppression in vitro

A marked suppression of immune function has long been recognized as a major cause of the high morbidity and mortality rate associated with acute measles. As a hallmark of measles virus (MV)-induced immunosuppression, peripheral blood lymphocytes (PBLs) isolated from patients exhibit a significantly reduced capacity to proliferate in response to mitogens, allogens, or recall antigens. In an in vitro system we show that proliferation of naive PBLs [responder cells (RCs)] in response to a variety of stimuli was significantly impaired after cocultivation with MV-infected, UV-irradiated autologous PBLs [presenter cells (PCs]. We further observed that a 50% reduction in proliferation of RCs could still be observed when the ratio of PC to RC was 1:100. The effect was completely abolished after physical separation of the two populations, which suggests that soluble factors were not involved. Proliferative inhibition of the RCs was observed after short cocultivation with MV-infected cells, which indicates that surface contact between one or more viral proteins and the RC population was required. We identified that the complex of both MV glycoproteins, F and H, is critically involved in triggering MV-induced suppression of mitogen-dependent proliferation, since the effect was not observed (i) using a recombinant MV in which F and H were replaced with vesicular stomatitis virus G or (ii) when either of these proteins was expressed alone. Coexpression of F and H, however, lead to a significant proliferative inhibition in the RC population. Our data indicate that a small number of MV-infected PBLs can induce a general nonresponsiveness in uninfected PBLs by surface contact, which may, in turn, account for the general suppression of immune responses observed in patients with acute measles.

Relative ability of different bovine leukocyte populations to support active replication of rinderpest virus

Bovine peripheral blood mononuclear cells (PBMC) were infected with the pathogenic Saudi isolate of rinderpest virus (RPV) in order to identify the cell subpopulation(s) susceptible to active replication of this virus. Flow cytometry analysis, using a monoclonal antibody recognizing the H glycoprotein of RPV, showed that monocytes were the main subpopulation in which the virus replicated, whereas <2% of lymphocytes expressed viral antigen. The activation of PBMC with concanavalin A before infection resulted in an increase in the capacity of lymphocytes to support RPV replication; >90% of CD4+ and CD8+ T lymphocytes expressed viral antigen at 3 days postinfection, although < or = 40% of gamma/delta T cells were productively infected. B-lymphocyte activation with pokeweed mitogen also resulted in increased replication of this virus in these cells, involving up to 40% of B lymphocytes. An enhancement of lymphocyte susceptibility to infection and active replication by RPV was observed upon coculture of RPV-infected PBMC on bovine endothelial cells. Such enhancement was most marked with the B-cell and CD4+ T-cell subpopulations. Contact between lymphocytes and extracellular matrix components did not alter the capacity of RPV to replicate in lymphocytes. This intercellular contact with endothelial cells increased the viability of certain lymphocyte subpopulations, but it alone could not explain the increased sensitivity to RPV. Intercellular signalling, which resulted in interleukin-2 receptor upregulation, probably played a role. In summary, monocytes are the main target for active, productive infection by RPV. Similar replication in lymphocytes depends on their activation state and on contact with accessory cells such as endothelial cells. These characteristics have important implications for virus traffic in vivo and the pathogenesis of this disease.

Evidence that measles virus hemagglutinin initiates modulation of leukocyte function-associated antigen 1 expression

Measles virus (MV), human immunodeficiency virus, Epstein-Barr virus, and other leukotropic viruses can modulate the expression of leukocyte function antigen 1 (LFA-1) on the surface of infected and nearby leukocytes. This ability to induce changes in LFA-1 expression may play an important role in the pathogenesis of these viruses. However, the mechanism(s) involved in virus-mediated regulation of LFA-1 is unknown. Evidence is presented in this report that it is the MV hemagglutinin (H) protein that initiates up-regulation of LFA-1 expression in leukocyte cultures infected with this virus. Indeed, comparison of the abilities of different MV strains to modulate LFA-1 expression, examination of published nucleotide sequences for the H proteins of different vaccine strains, and competitive inhibition assays using oligopeptides homologous or heterologous to a region of the H protein gene encompassing amino acid 116 (from the amino terminus) all suggest that it is this portion of the H protein that is responsible for MV-induced alteration of LFA-1. These comparisons also support the hypothesis that there is a relationship between the abilities of different MV strains to alter LFA-1 expression and their pathogenic potentials.

Increased expression of adhesion molecules (CD54, CD29 and CD44) on fibroblasts infected with cytomegalovirus

The expression of ICAM-1 (CD54), beta 1 integrin (CD29), and CD44 on cytomegalovirus (CMV)-infected human embryonic fibroblasts (HEF) was analyzed by flow cytometry. The expression of these adhesion molecules increased significantly on CMV-infected HEF, on days 2 and 5 after inoculation, compared to uninfected HEF. However, the expression of these adhesion molecules decreased on herpes simplex virus (HSV)-1 and varicella-zoster virus (VZV)-infected HEF. Increased expression was not observed on HEF treated either with inactivated CMV or with supernatant fluid of CMV-infected cells. The addition of anti-cytokine (TNF-alpha, IL-1 beta, or IFN-gamma) antibodies had no effect on the increase of these adhesion molecules. This suggests that the increase in CD54, CD29, and CD44 on CMV-infected cells requires active virus replication and was not mediated by a soluble factor released from CMV-infected cells. Changes in adhesion molecules on CMV-infected fibroblasts may contribute to inflammation induced by CMV infection.

Aspects of canine distemper virus and measles virus encephalomyelitis

Canine distemper (CD) is a frequently fatal, systemic morbillivirus infection in the dog and other carnivores: encephalomyelitis is the common cause of death. Susceptibility to canine distemper virus (CDV) is now recognized in a wide range of non-domestic animals, most recently in captive lions, tigers and leopards. Furthermore, closely related viruses have produced CD-like diseases in marine mammals. CDV induces an inclusion-body encephalomyelitis in the dog and demyelination is often a conspicuous feature. Myelin injury is associated with the presence of virus but the mechanism of demyelination remains incompletely understood. Oligodendrocyte infection may be defective, as has been shown in vitro. CDV and measles virus (MV) produce similar systemic disorders in their respective hosts but differ markedly in the frequency of central nervous system (CNS) involvement, and in the pathogenesis of the more common neurological sequelae. Both CDV and MV have been considered as multiple sclerosis agents, and the association of CDV with other human disease has been suggested.

Infection of leucocytes by measles vaccine viruses Edmonston-Zagreb and Enders-Moraten has different consequences: potential mechanism for increased vaccine efficacy or aberrant activity in field trials

The abilities of two measles vaccine virus strains, Edmonston-Zagreb (E-Z) and Enders-Moraten (E-M), to infect and modify the activities of U937 monocytoid and peripheral blood mononuclear leucocytes (PBMLs) were compared with each other and with changes resulting from infection of these cells by a wild-type measles virus (MV). Both the E-Z and wild-type MV were shown to infect U937 and PBMLs and (1) to markedly increase expression of leucocyte function antigen 1 (LFA-1) on leucocytes present in infected cultures; (2) to increase cell-cell interaction; (3) to grow and disseminate readily in both types of leucocyte cultures; and (4) to persist for more than 7 days in these cultures despite the presence of MV-specific neutralizing antibodies. In contrast, the E-M virus did not grow well in unstimulated PBMLs and, although it did grow well in U937 cells, it did not noticeably alter the expression of LFA-1 on these cells, did not induce significant cell-cell interaction, and was rapidly eliminated from these cultures if MV-specific neutralizing antibodies were present. The possible relationship of these findings to the increased protective efficacy and untoward effects associated with the E-Z MV vaccine is discussed.