Glycoproteins of Pneumocystis carinii: characterization by electrophoresis and microscopy

Glycoproteins are integral components of cell-surface structure and participate in adherence of pathogenic microbes to host cells. We have initiated studies of the glycoproteins of Pneumocystis carinii. Biotin-conjugated lectins, followed by reaction with avidin-peroxidase, were used to detect glycoproteins in electrophoretically separated proteins of P. carinii and on whole organisms when using light microscopy. Glycoproteins of P. carinii were clearly different from rat cell glycoproteins. Multiple glycoproteins were present in P. carinii and exhibited intense reactivity to both concanavalin A and wheat-germ agglutinin. Those lectins that reacted with the electrophoretically separated proteins also stained both alcohol-fixed P. carinii and the extracellular granular material present only in P. carinii preparations. In electron micrographs of P. carinii, which were stained with colloidal-gold-labeled concanavalin A, we found that the lectin bound to the outer surface of the organisms and to the tubular extensions emanating from the exterior surface.

Altered threshold for the induction of graft-versus-host immunodeficiency following murine cytomegalovirus infection. Host and donor contributions

Acute murine cytomegalovirus (MCMV) infection enhances the ability of parental spleen cells to induce graft-vs.-host immunodeficiency (GVHID) in F1 hybrid mice when the two processes occur simultaneously in the recipient. The present study assessed GVHID as the ability of spleen cells to generate in vitro cytotoxic T lymphocyte responses to trinitrophenyl-modified syngeneic cells. The results indicate that MCMV infection not only reduces the number of parental spleen cells required to induce GVHID, but accelerates the onset of GVHID, which occurs as early as 3 days after cell and virus challenge. To determine whether MCMV infection exerts this synergistic effect primarily through the donor or the host component, we examined the effect of MCMV infection of either donor mice or recipient mice at 3, 10, and 17 days prior to spleen cell transfer. Two weeks after cell transfer, splenocytes were tested for their ability to generate CTL. When donor mice were infected with MCMV three days prior to cell transfer, the ability of donor cells to induce GVHID was reduced. In contrast, MCMV infection of the recipients three days prior to cell transfer increased their susceptibility to GVHID induction. Infection of either donor or host mice 10 days or 17 days prior to parental spleen cell transfer had little effect on the ability to induce or resist GVHID when compared with sham-infected mice. Thus, acute MCMV infection can modulate the severity of GVHID depending on whether it is the donor or the host that is infected. The ability of acute MCMV to alter the course and severity of GVHID may be relevant for human bone marrow transplants in which preceding CMV infection has been associated with chronic GVH. In this setting, CMV may lower the threshold necessary to induce a GVH reaction.

Aerosol administration of antiviral agents to treat lung infection due to murine cytomegalovirus

Cytomegalovirus (CMV) pneumonia causes significant morbidity and mortality in bone marrow transplant recipients and in patients with AIDS. 9-(1,3-Dihydroxy-2-propoxymethyl) guanine (ganciclovir) and phosphonoformic acid (PFA) demonstrate activity against CMV in human infections, although recurrent CMV and systemic drug toxicity frequently develop. We examined the efficacy of aerosol administration of antiviral agents against murine CMV (MCMV) infection. Animals were inoculated with MCMV intranasally and were treated with oral ganciclovir; with aerosolized ganciclovir, PFA, or ribavirin; or with buffer. MCMV in lung and salivary gland homogenates was quantified by plaque assay. Oral ganciclovir (200 mg/kg per day) reduced titers of MCMV in both tissues by greater than 95%. Aerosolized ganciclovir, 100 and 200 mg/kg per day, reduced lung titers of MCMV by 93% and 97%, respectively. Aerosolized PFA, 20 and 200 mg/kg per day, reduced lung titers of MCMV by 60% and 68%, respectively. Aerosolized ganciclovir and PFA inhibited replication of MCMV in salivary glands substantially less than did oral administration of either agent. Our results suggest that aerosol administration of antiviral agents can potently and selectively inhibit replication of MCMV in the lung.

Interstitial pneumonitis during murine cytomegalovirus infection and graft-versus-host reaction. Characterization of bronchoalveolar lavage cells

Acute murine cytomegalovirus (MCMV) infection alters the course of graft-vs-host (GVH) disease involving major histocompatibility (MHC) antigens and induces interstitial pneumonitis. F1 (B10 x B10.BR) mice given 20 x 10(6) B10.BR spleen cells and MCMV (1 x 10(5) plaque-forming units [PFU]) develop severe, diffuse pneumonitis not seen with either MCMV or GVH alone. As one index of the host immune processes operating in the lungs during MCMV/GVH pneumonitis, we examined the types of cells recovered from the lung by bronchoalveolar lavage (BAL) during pneumonitis. During MCMV/GVH pneumonitis, the total cells recovered significantly increased, due primarily to an influx of Thy 1.2 lymphocytes. Characterization of cells using multiparameter flow cytometric analysis revealed that greater than 80% of all BAL cells were Thy 1.2-positive lymphocytes of donor origin. In addition, donor Thy 1.2-positive cells were of both the L3T4+ (43% of BAL cells) and Lyt 2+ (38% of BAL cells) phenotype. Thus, MCMV infection during GVH to MHC antigens induces interstitial pneumonitis, characterized by an influx of T lymphocytes (both helper and suppressor/cytotoxic) from the donor. The antigenic specificity of these cells is not known.

Is cytomegalovirus interstitial pneumonitis in transplant recipients an immunopathological condition?

The conventional explanation for the high fatality rate due to cytomegalovirus (CMV) pneumonitis among allogeneic transplant recipients is that immunosuppression renders the host unable to control replication of this opportunistic agent. However, evidence from studies in man and the murine model of CMV show that virus replication in the lung is unrelated to the development of pathological effects, and that a host immune response is required for the induction of pneumonitis. Thus the hypothesis is that limited CMV replication in the lungs leads to display of a virus-coded protein, which is recognised by host T-cells, and that the pneumonitis is due to an uncontrolled accumulation and recruitment of such cells in the lungs. The reason why CMV is found in the lungs of patients with the acquired immunodeficiency syndrome (AIDS) without producing pneumonitis is probably because these patients cannot mount the pathogenic T-cell response. According to the hypothesis stated here, if the immune capabilities of AIDS patients can be restored, life-threatening CMV pneumonitis may develop.

Detection of antibody to murine cytomegalovirus by enzyme-linked immunosorbent and indirect immunofluorescence assays

We have compared murine cytomegalovirus (MCMV) antibody determination by enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence assay. A comparison of antibody detection with 146 serum samples at a 1:20 dilution showed 100% agreement (60 negatives and 86 positives) between the assays. There was close agreement of endpoint determinations of sera by both methods. After experimental MCMV infection, antibody to MCMV was detected by both assays as early as day 7, and high titers persisted as late as 6 months. In contrast to immunocompetent littermates, athymic nude mice did not develop antibody after infection. Mice lacking antibody detectable by ELISA were susceptible to lethal MCMV challenge. In a survey of animals from five commercial sources, MCMV antibody was not detected unless mice were experimentally infected. MCMV antibody determination by ELISA is a convenient method, comparable to the indirect immunofluorescence assay in sensitivity and specificity.

Review of 59 patients hospitalized with animal bites

We reviewed the charts of 59 pediatric and adult patients hospitalized because of animal bites (46 dog bites, 10 cat bites, 3 monkey bites). The bites of 40 of the 59 patients were infected at the time of admission. Gram-stained specimens correctly predicted the infecting bacteria in only 5 of 20 cases. Eighty-three percent of the bacterial isolates were penicillin-susceptible. Before admission 14 patients had received outpatient antibiotic prophylaxis and the infections in 11 of these 14 patients were caused by bacteria susceptible to the prophylactic antibiotic. Complications were more common if antimicrobial therapy had not been altered according to susceptibility testing results. Of the 59 patients 19 were admitted immediately after being bitten because of severe uninfected bites. Of these 19 patients 18 received prophylactic antibiotics and none developed a serious complication.

Modification of acute murine cytomegalovirus adrenal gland infection by adoptive spleen cell transfer

Homozygous (nu/nu), athymic nude mice, infected with murine cytomegalovirus (MCMV), develop unremitting and ablative virus infection involving both the adrenal cortex and medulla. During acute infection, adoptive transfer of MCMV-immune, but not naive, spleen cells suppressed virus replication in the adrenal glands, but not the lungs or salivary gland. T lymphocytes, not macrophages or B cells, were responsible for limiting viral replication. The effect by donor cells was restricted by compatibility at the major histocompatibility locus. Restriction of MCMV replication in the adrenal gland was associated with T lymphocytes of the L3T4 phenotype. Thus, T-cell immunity is critical in regulating MCMV replication in the adrenal glands, and T lymphocytes restricted by class II major histocompatibility antigens mediate this effect.

Human cytomegalovirus replicates in gamma-irradiated fibroblasts

Because of the unique interdependence of human cytomegalovirus (HCMV) and the physiological state of the host cell, we evaluated the ability of human foreskin fibroblasts (HFF), exposed to gamma radiation, to support HCMV growth. Irradiation of HFF with 2,500 rADS prevented cellular proliferation and suppressed cellular DNA, but not RNA or protein synthesis. Treatment of HFF cells with 2,500 rADS 6 or 48 hours prior to infection did not alter the time course or virus yield during HCMV replication. Virus plaquing efficiency in irradiated cells was comparable to that of nonirradiated cells. As judged by thymidine incorporation and BUdR inhibition of virus replication, HCMV infection induced both thymidine kinase activity and host cell DNA synthesis in irradiated cells. In addition, virus could be recovered from HFF exposed to radiation 0-2 days after infection with HCMV. These studies indicate that the damage to cells by gamma irradiation does not alter the capacity of host cells to support HCMV replication.

Encephalomyocarditis virus can bind to and transfect non-permissive cells

Mouse embryo fibroblasts and mouse adrenal tumor cells support the replication of encephalomyocarditis (EMC) virus, whereas rat glial and rat hepatoma cells are non-permissive. These differences in susceptibility were not due to the lack of virus attachment to rat cells. The findings that rat cells could be transfected with RNA derived from EMC virus indicates that the block in viral replication in these cells occurs at some point between attachment and uncoating of virus, probably at the level of uncoating.

Murine cytomegalovirus adrenalitis in athymic nude mice

During studies of the pathogenesis of murine cytomegalovirus (MCMV) infection in athymic nude mice, we noted striking virus involvement of the adrenal glands. Because patients with the acquired immunodeficiency syndrome (AIDS) have recently been reported to have adrenal necrosis and evidence of infection of the adrenal gland with human cytomegalovirus (HCMV), we have further evaluated adrenal gland involvement during MCMV infection. Following virus inoculation, MCMV replicated to high titer in the adrenal glands of T-cell deficient, homozygous nude mice, but not heterozygous littermates with intact T-cell function. Concomitant with the high titers of virus, there appeared overt histological evidence of herpes-virus virus infection accompanied by patchy necrosis of adrenal cortical and medullary tissues. Acyclovir, which inhibits growth of MCMV, reduced virus replication in the adrenal gland. Similarly, virus replication was diminished in homozygous nude mice immunologically reconstituted by infusion of normal spleen cells three weeks prior to infection. Thus, in the absence of functioning T lymphocytes, MCMV can infect and replicate in adrenal tissues causing a progressive destructive adrenalitis.

Inhibition of murine cytomegalovirus lung infection and interstitial pneumonitis by acyclovir and 9-(1,3-dihydroxy-2-propoxymethyl)guanine

We compared the effects of acyclovir (ACV) and 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) on murine cytomegalovirus (MCMV) replication in lung and salivary gland tissues, the evolution of interstitial pneumonitis in vivo, and MCMV replication in mouse embryo cells in vitro. As measured by plaque reduction, ACV was more active than DHPG in vitro. In vivo, whether administered orally by gastric intubation or in the drinking water, or subcutaneously, DHPG was more effective than ACV in reducing MCMV titers in lung or salivary gland tissues. This was true in both normal and cyclophosphamide-treated mice. Neither drug was able to prevent MCMV interstitial pneumonitis, despite substantial reductions in virus titer, but both drugs reduced the severity of the pneumonitis.

Alteration of bronchoalveolar cells during murine cytomegalovirus interstitial pneumonitis

In BALB/c mice, murine cytomegalovirus (MCMV) in conjunction with a single dose of cyclophosphamide (CP) induces a diffuse interstitial pneumonitis not seen with either virus or CP alone. To gain insight into the host immune mechanisms operating in the lung during interstitial pneumonitis, we examined the cells recovered in bronchoalveolar lavage (BAL) fluids of mice with MCMV with and without CP. During MCMV interstitial pneumonitis, there was a significant increase in the total BAL cells recovered, primarily because of an influx of lymphocytes bearing the Thy 1.2 marker. Although the number of cells with Lyt 1 and Lyt 2 markers increased, the most significant increase was in the proportion of lymphocytes with surface asialo-GM1. Delineating the roles of these various cell populations may provide insight into the pathogenetic mechanisms leading to CMV interstitial pneumonitis.

The relation of viral replication to interstitial pneumonitis in murine cytomegalovirus lung infection

Using a murine model of murine cytomegalovirus (MCMV) interstitial pneumonitis, we examined the relation between the virus content of the lung and lung disease. While MCMV alone does not cause lung disease, interstitial pneumonitis was present in all mice receiving both MCMV and a single dose of cyclophosphamide. In this case the severity of disease, judged by increases in wet weight of the lung, was proportional to the virus content of the lung. Although both acyclovir (50 mg/kg per day) and passive antibody administration reduced the MCMV titers in lung tissues by greater than 90%, histological evidence of interstitial pneumonitis was present in all animals. However, both virus inhibitors reduced the severity of interstitial pneumonitis in treated mice. While transient alterations in host immunity are necessary to induce interstitial pneumonitis after MCMV infection, the severity of interstitial pneumonitis seems to reflect the burden of virus replication. Reduction of virus growth does not prevent, but may moderate, MCMV interstitial pneumonitis.

Host genetic factors influence murine cytomegalovirus lung infection and interstitial pneumonitis

We evaluated the influence of host genetic factors on the course of murine cytomegalovirus (MCMV) lung infection after intranasal inoculation and on the development of interstitial pneumonitis after virus and cyclophosphamide (CP) administration. Susceptibility to virus replication in the lungs of various inbred murine strains was inherited as an autosomal dominant trait, which was associated with the H-2 locus. Similarly, the development of MCMV interstitial pneumonitis was inherited as an autosomal dominant, polygenic trait. Susceptibility to lung infection was necessary, but not sufficient for MCMV interstitial pneumonitis. Non-H-2-associated factors were also needed and probably related to CP metabolism or the character of immune recovery after CP administration. Therefore, inheritable host factors influence both susceptibility to MCMV lung infection and the genesis of MCMV interstitial pneumonitis.

Murine cytomegalovirus-induced macrophage dysfunction

Macrophages infected in vitro with murine cytomegalovirus (MCMV) manifest depressed phagocytic uptake of a variety of particles within hours after the initiation of infection. Analysis of kinetics of uptake of radiolabeled Staphylococcus aureus by MCMV-infected macrophages indicates that the diminished uptake results from a depression in the calculated maximum velocity of uptake (Vmax) with the apparent Michaelis constant (KM) remaining unaltered. This pattern of altered uptake is typical of that seen after manipulations that affect the surface interactions of macrophages with ingestible particles. Coincubation of macrophages and radiolabeled Staphylococcus with opsonizing antibody resulted in normalization of the phagocytic rates. The surface localization of the defective phagocytosis was further confirmed by light and scanning electron microscopy of the macrophages incubated with Staphylococcus or latex spherules. These data indicate that defective macrophage surface that interferes with the initial macrophage-particle interactions that initiate nonimmune phagocytosis.

Verapamil inhibits influenza A virus replication

Calcium channel blockers reduce Ca++ flux through membrane channels and may inhibit intracellular Ca++-dependent synthetic and regulatory activities by binding to calmodulin. We have found that Verapamil, a calcium channel blocker, inhibits influenza virus replication in Madin-Darby canine kidney cells and in murine pulmonary macrophages and that this antiviral effect occurs with drug addition late in the replication cycle. Chlorpromazine, a drug which binds to calmodulin, also inhibited influenza virus replication in these tissue culture systems. We suggest that Verapamil and chlorpromazine inhibit influenza virus replication by interfering with calmodulin-dependent intracellular activities necessary for late synthetic steps or virus assembly steps and that calcium channel blockers provide a new probe for investigating influenza virus replication.

Murine peritoneal macrophages support murine cytomegalovirus replication

Because there have been different conclusions regarding the susceptibility of murine macrophages to murine cytomegalovirus (MCMV) infection and replication, we have undertaken a detailed comparison of MCMV infection of macrophages with that of a permissive cell line, mouse embryo cells. Although both cell lines undergo productive infections with MCMV, there are marked differences in certain aspects of the viral replication which may account for some of the different conclusions regarding the MCMV cycle in macrophages. Although both cell lines produce MCMV after infection, the time course of the infection differed markedly between the cell types. Similarly, the proportion of infected macrophages that are releasing infection virions is much smaller than the proportion of a comparably infected mouse embryo cell culture. Tissue culture passage of MCMV first enhanced (after one passage) and then reduced the infectivity of the virus for macrophages in vitro. The delayed time course and lesser production at early intervals after infection of macrophage cultures could not be attributed to demonstrable inhibitors or to replication in contaminating fibroblasts in the macrophage cultures.

Replication of encephalomyocarditis virus in various mammalian cell types

Recently, the biological and biochemical characteristics of EMC virus have received considerable attention, but little is known concerning the relative susceptibility of various mammalian cells to EMC virus. In this study, a variety of mammalian cell types was evaluated for susceptibility to the M strain of EMC virus by comparing peak viral titers, time course of infection, plaquing efficiency, and formation of viral antigens. Infection of all murine and guinea pig cell types resulted in substantial virus replication and induction of viral antigens in greater than 95% of cells. Human cell lines supported replication with a slower time course, but significant increases in viral yield and plaquing efficiency occurred with viral adaptation following successive replication cycles in human cells. All rat cell lines were relatively resistant to EMC virus infection and replication, and less than 1% of rat cells expressed viral antigens. Attempts were unsuccessful to adapt virus by successive replication cycles in rat cells. The possible reasons for the relative resistance of rat cells are currently under investigation.

Ultraviolet irradiation of murine cytomegalovirus

Ultraviolet irradiation of murine cytomegalovirus (MCMV) caused a rapid dose-related decline in virus infectivity, manifested by virus antigen induction, and in virus production as measured by plaque formation and infectious centre assay. The virus survival curve was multi-component, suggesting host cell-assisted reactivation. Multiplicity reactivation and photoreactivation of MCMV were not observed in these experiments. Productive infection was more sensitive to u.v. irradiation than was virus antigen production, indicating differential inactivation of virus functions. The effects of u.v. irradiation were similar in most respects to those reported for human cytomegalovirus.