Partial genome sequence of murine gammaherpesvirus 72 and its analysis

Murine gammaherpesvirus 68 (MHV-68)-infected mouse is a well known model for studies of Epstein-Barr virus (EBV)-related lymphoproliferative diseases (LPD). Murine gammaherpesvirus 72 (MHV-72) has been considered a close relative of MHV-68 but its replication in murine mammary gland cells and kinetics of infection of mice were found to be different. Pathological studies of a long-term-infection of mice revealed a similar or higher malignancy development rate in MHV-72-infected mice as compared with that of MHV-68. Previous comparison of MHV-72 with MHV-68 revealed their diversity in M3, MK3, and M7 genes encoding the chemokine-binding protein, immune evasion protein and glycoprotein 150, respectively. In this study, a portion (22,899 bp) of MHV-72 genome sequence was determined, analyzed and compared with that of MHV-68. Nucleotide sequences of 13 structural and 6 non-structural genes of MHV-72 and deduced amino acid sequences revealed their identity to those of MHV-72 except for differences in 9 nucleotides and 8 amino acids, occurring in 5 genes and their proteins. Due to these differences, 4 structural proteins encoded by ORF20, ORF26, ORF48, and ORF52, respectively, and a non-structural protein encoded by ORF4, all of MHV-72, are predicted to have altered hydrophilicity and surface exposure in comparison with their MHV-68 counterparts. These differences obviously contribute to some different pathogenetical features of these viruses and could explain the reduced immunogenicity of MHV-72 in relation to MHV-68, allowing MHV-72 to escape the host immune surveillance.     

Susceptibility of mouse mammary glands to murine gammaherpesvirus 72 (MHV-72) infection: evidence of MHV-72 transmission via breast milk.

Murine gammaherpesvirus 72 (MHV-72) is a virus of wild rodents and serves as a convenient small animal model to understand the pathogenesis of Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV8) infection. In laboratory mice MHV-72 causes an acute infection of lung epithelial cells and establishes the latency in B lymphocytes. In this study, we investigated athymic nude and immunocompetent mice for distribution of virus in organs after infection with MHV-72. Ten days following subcutaneous dorsal injection of nude mice, virus replicated in lungs, lymphoid organs, salivary glands and also in mammary glands. The virus titre decreased by day 21 post-infection in former tissues, but increased in mammary glands. Presence of virus DNA sequences was detected in the lymphoid and non-lymphoid tissues until the death of the animals (about 1 month post-infection). Infection of immunocompetent mice with MHV-72 induced replication of virus up to 42 days post-infection in mammary glands reaching the highest level of infectious virus at day 8 post-infection. These data show that there is latent infection in mice never detected before. Moreover, virus DNA was detected using nested PCR (by amplification of a portion of gp150 gene sequence) in the mammary glands and the milk of mouse mothers infected with MHV-72 2 days before delivery. We demonstrated the presence of virus DNA also in the milk removed from the stomach of non-infected newborn mice, which were nourished by infected mothers (wet-nurses) for 1 or 2 days. The failure to detect the virus DNA in newborn mice lungs confirmed that they did not become infected from wet-nurses by the intranasal route. This suggests that MHV may be naturally transmitted to newborn mice via breast milk.     

Pathogenetical characterization of isolate MHV-60 of mouse herpesvirus strain 68

Infection of mice with mouse herpesvirus strain 68 (MHV-68) is an excellent small animal model of gammaherpesvirus pathogenesis in a natural host. We carried out comparative studies on MHV-60, another isolate of MHV-68. The acute infection of BALB/c mice inoculated intranasally (i.n.) with MHV-60 as well as its impact on tumor development were investigated. During the acute phase of infection the lungs were the main tissues infected. Our results show that MHV-60 has similar pathological features like other 4 isolates so far examined, namely MHV-72, MHV-78, MHV-Sumava inclusive of MHV-68. Nevertheless, MHV-60 differed from other isolates in following features: (i) the acute phase of infection was established very soon and lasted 10 days post infection (p.i.) in contrast to 14-28 days p.i. in the abovementioned isolates with a peak on days 3-5 p.i. The virus could also be recovered from the spleen, thymus and kidneys but not in other investigated organs. A lymphoproliferative response was associated with splenomegaly. At this time an increase in the number of leukocytes and appearance of atypical leukocytes in peripheral blood were observed. (ii) the infection was localized in the lungs and spleen, while in other isolates it was detected in a much broader scale of organs, and (iii) the acute phase of infection was accompanied by a massive splenomegaly, which was characteristic for the chronic phase of infection. Despite the fact that after clearance of the acute infection the virus was hardly detected, the tumor formation was later observed in 22% of infected mice as compared to 5% in control non-infected mice.     

Comparative studies between nude and scid mice on the growth and metastatic behavior of xenografted human tumors

The growth and metastatic behavior of three human tumor cell lines and a human colon carcinoma previously passagedin vivo were compared between nude mice and scid mice after xenotransplantation. The three human tumor lines included a bladder carcinoma (T24B), a melanoma (RPMI 7931) and alacZ gene-transduced breast cancer (MDA-MB-435 BAG). ThelacZ gene codes for -galactosidase, which can be stained blue with chromogenic substrate X-gal, thus allowing the highly sensitive detection and quantitative examination of human cancer metastasis in host mice. Adult (7–14 weeks) NMRI nude and C.B-17 SCID mice were inoculated with 0.5–5 × 10⁶ tumor cells s.c. Comparable take rate, latent period and growth rate of implanted tumors were observed in nude and scid mice for each of the cell lines tested. At the time of autopsy, which varied from 6 to 11 weeks after inoculation, a significantly higher incidence of spontaneous lung metastasis was discovered in scid mice (96%) than in age-matched nude mice (27%, totalP < 0.001).In vitro assays for NK cell-mediated cytotoxicity revealed no significant differences between the two strains of mice. Our results suggest that nude and scid mice are equally suitable for propagating human tumors. However, the metastatic capacity of human tumor cells appears to be better expressed in scid mice. Scid mice may therefore provide an advantageous model for the study of human tumor metastasis.     

Spontaneous Abortion in Immunodeficient SCID Mice

PROBLEM: Immunodeficient SCID mice on the CB-17 have been used to test the role of “rejection” in a xenogeneic blastocyst transfer model of recurrent miscarriage, but interpretation of the data requires knowing syngeneic within-species matings have a high success rate and do not require immunotrophic factors expected only in immunocompetent non-T-cell deficient mice. METHOD: Resorption rates were studied in a SCID CB-17 barrier facility that provided the mice used to test the role of immunology in the resorption model. RESULTS: Spontaneous resorption in syngeneically mated immunodeficient SCID mice on the CB-17 background occurred at an unexpectedly high rate and could not be prevented by treatment with anti-asialo GM1 antibody or GM-CSF, both of which are effective in ameliorating abortion in DBA/2J-mated CBA/J mice. Immunocompetent CB-17 +/+ mice showed an even higher rate of loss. The latter was also not affected by treatment with anti-asialo GM1 antibody or by GM-CSF and was not prevented by tetracycline (which is effective in the DBA/2-CBA/J system) or progesterone treatment. Mating experiments showed a scid/+ × scid//+ cross gave the highest rate of loss, and it appeared that the presence of +/+-type embryos in the uterus could be augmenting abortion with selective discrimination against scid/scid embryos. High abortion rates were associated both with appearance of a coagulase-negative Staphylococcus sp. in feces and with loss of one component of the SPF flora. Decidual tissue from mated CB-17 +/+ mice showed premature release of TNF-cc in absence of TGF-β2-related suppressor activity, and vascular lesions (fibrinoid necrosis), varying in extent, were associated with both scid/scid × scid/scid and +/+ × +/+ pregnancies. TNF-α also appeared prematurely in pregnant scid/scid mice, but the levels were lower (and areas of necrosis smaller than in +/+ × +/+ pregnancies). Outcrossing onto a C57B1/6 background dramatically reduced the abortion rate, indicating an important genetic effect on susceptibility with heterogeneity protecting against abortion. CONCLUSIONS: SCID mice on the CB-17 background do not have a high rate of successful syngeneic pregnancies, and a TNF-α induced vasculopathy may be responsible. Abortion was not caused by immunodeficiency leading to loss of immunotrophism because immunocompetent non-SCID CB-17 mice had a higher rate of loss. Factors augmenting the abortion rate included the presence of embryos of the +/+ genotype in the uterus and treatment with anti-asialo GM1 antibody. Abortion rates were not reduced by treatments effective in the DBA/2-mated CBA/J mouse model but were reduced by re-establishing a new colony with defined flora (a temporary effect) and by outcrossing mice with a different (C57B1/6) background. Together, the data suggest an infectious trigger (identity uncertain) of the vasculopathy and an important genetic influence on susceptibility with heterozygosity and a SCID mouse mutation providing against abortion a degree of protection.     

Immunophenotypic study of atypical lymphocytes. Generated in peripheral blood and spleen of nude mice After MHV-72 infection

Inbred athymic nude mice (BALB/c) were injected subcutaneously with the wild-type murine gammaherpesvirus 72 (MHV-72), which has been shown to induce the infectious mononucleosis (IM)-like syndrome in immunocompetent mice. The mice were also injected with UV-irradiated MHV-72. We studied the pattern of acute and chronic infection in the blood cells of the nude mice and detected viral DNA sequences in the infected leukocytes by polymerase chain reaction (PCR) technique up to when the animal died, close to 1 month postinfection. Using the UV-irradiated virus that induces an increase in mouse survival time, the viral sequences were present in the blood up to 3 months postinfection, then disappeared. We detected atypical lymphocytes in the blood of mice infected with both wt and UV-irradiated viruses. These atypical cells were similar in shape to those present in the blood of patients with IM induced by Epstein-Barr virus (EBV). Via Unscheduled DNA Synthesis (UDS), DNA synthesis was demonstrated in the atypical cells whose phenotype is identical to that of B cells, as shown with a panel of monoclonal antibodies. By double immunofluorescence staining, using an hyperimmune anti-MHV-72 serum and an anti-IgG + IgM + IgA monoclonal antibody, we demonstrated that these atypical B cells express some viral antigens. Contrary to the immunocompetent mice, the nude mice did not develop splenomegaly after infection with wt virus, probably due to the lack of T cell subsets. However, we observed an increase of nude mice B cells in the spleen. The nude mice died 1 month postinfection showing a high frequency (40%) of atypical lymphoblast-like B-cells in the blood; the increase in natural killer (NK) cell number was not detected after infection. Such findings suggest that NK cells probably did not play an important role in immune response to the MHV infection in nude mice. Finally, this mouse model could play an important role in antigammaherpesviral therapy of immunocompromised patients.     

Intranasal inoculation of Mycoplasma pulmonis in mice with severe combined immunodeficiency (SCID) causes a wasting disease with grave arthritis.

Mycoplasma pulmonis or Myc. pneumoniae were inoculated intranasally to C.B-17 scid/scid mice (severe combined immunodeficient (SCID) mice). Immunocompetent C.B-17 mice were inoculated as controls. During the observation period of 5 weeks the mice were killed and necropsied. Mycoplasma pulmonis was recovered from all of the inoculated mice, and dissemination to various tissues increased with time. SCID mice, unlike immunocompetent mice, did not show lung lesions but exhibited severe inflammatory changes of the joints. Mycoplasma pulmonis, however, was isolated both from the lungs and the articular lesions. In addition, SCID mice infected for more than 3 weeks suffered from a pronounced loss of weight and emaciation. In the experiment with Myc. pneumoniae the agent could be reisolated, but lesions were not found in any of the infected mice. Mycoplasma pulmonis infection in SCID mice may be useful as a model of arthritis in immunodeficient humans.     

Immunophenotyping of leukocytes in peripheral blood of BALB/c mice infected with mouse herpesvirus isolate 72

We characterized leukocytes in peripheral blood of BALB/c mice infected with mouse herpesvirus isolate 72 (MHV-72) representing an isolate of mouse herpesvirus strain 68 (MHV-68, species Murid herpesvirus 4, genus Rhadinovirus, subfamily Gammaherpesvirinae, family Herpesviridae) (van Regenmortel et al., 2000). In acute infection (up to day 30 post infection (p.i.)) the number of CD8+ T cells increased, reaching a maximum at day 11 p.i. This increase correlated with that of CD4+ T, activated CD 19+ B and natural killer (NK) cells. At day 30 p.i. the numbers of CD4+, CD8+, CD14+ and CD19+ cells decreased to normal values. A similar increase in the number of these cells was observed at day 730 p. i. In the course of persistent infection (after day 30 p.i.) some of the mice developed a leukemia-like syndrome characterized by an increase in the number of leukocytes and appearance of atypical, blastic immature forms of leukocytes. The latter forms of leukocytes were characteristic by an increased amount of argyrophilic proteins. These results show further similarities between MHV-72 (another isolate of MHV-68) and EBV infections and justify the use of MHV-68 or MHV-72 as an appropriate mouse model for the study of EBV infection of humans.     

A quick procedure for identifying doubly homozygous immunodeficient scid beige mice

This article describes a rapid and reliable procedure for identifying mice which are doubly homozygous at the scid and beige (bg) loci starting from CB17 scid (no T and B cells) and B6 bg mice (no NK activity). The [scid, bg] mice are directly identified in the F2 progeny by monitoring (1) the hypogammaglobulinemia for the scid gene and (2) the prolonged bleeding associated with the bg gene. Like CB17 scid mice, the [scid, bg] mice show a high susceptibility to infections and die early in life unless they are protected against potential infections. This is achieved by a graft of splenocytes plus bone marrow cells from (B6 bg x CB17 scid) F1 mice. These [scid, bg] mice combine the bg and scid immunodeficiencies and should be better recipients for xenografts than classical scid mice.     

Clearance of Chlamydia trachomatis– induced polyserositis in SCID mice requires both CD4+ and CD8+ cells

To characterize the role of specific lymphocyte subsets in Chlamydia trachomatis infection, we established a murine model using the mouse pneumonitis agent (MoPn) of C. trachomatis and C.B-17 scid/scid (SCID) mice which lack functional B and T cells. After intraperitoneal inoculation with the bacteria, SCID mice developed polyserositis with pleuritis, pericarditis, and perihepatitis. Within 8 weeks post infection, SCID mice succumbed to the disease, whereas immunocompetent congenic C.B-17+/+ mice resolved the infection. Adoptive transfer of immune spleen cells into MoPn-infected SCID mice resulted in a complete elimination of the agent and prevention of polyserositis as measured by quantitative chlamydial culture, direct immunofluorescence and histopathological analysis. Selective reconstitution of MoPn-infected SCID mice with immune B lymphocytes, CD4⁺ T cells or CD8⁺ T cells alone did not influence the chlamydial load in the lung and liver of infected SCID animals, resulting in a polyserositis as observed in untreated MoPn-infected SCID mice. However, co-transfer of both CD4⁺ T cells and CD8⁺ T cells led to a significant reduction of chlamydiae in quantitative organ culture coupled with unremarkable histopathology. These data confirm that T cell-mediated immune responses are essential for immune protection in chlamydial infection, although total eradication of the agent could not be achieved. Further experiments are needed to stress the importance of a concerted action of B and T lymphocytes, as indicated by the complete protective efficacy of transferred splenocytes. Received: 9 April 1998     

Murine gammaherpesvirus-68 (MHV-68) is not horizontally transmitted amongst laboratory mice by cage contact

Abstract

Murine gammaherpesvirus-68 (MHV-68), a natural pathogen of mice, is being evaluated as a model of Epstein Barr Virus (EBV) infection for use in investigation of the effects of immunomodulatory therapy on herpesvirus pathogenesis in humans. Immunosuppressive agents are used for treatment of a variety of autoimmune diseases as well as for prevention of tissue rejection after organ transplantation and can result in recrudescence of latent herpesvirus infections. Prior to examination of MHV-68 as a suitable model for EBV, better characterization of the MHV-68 model was desirable. Characterization of the MHV-68 model involved development of assays for detecting virus and for demonstration of safety when present in murine colonies. Limited information is available in the literature regarding MHV-68 transmission, although recent reports indicate the virus is not horizontally spread in research facilities. To further determine transmission potential, immunocompetent and immunodeficient mice were infected with MHV-68 and co-habitated with naïve animals. Molecular pathology assays were developed to characterize the MHV-68 model and to determine viral transmission. Horizontal transmission of virus was not observed from infected animals to naïve cagemates after fluorescence microscopy assays and quantitative PCR (qPCR). Serologic analysis complemented these studies and was used as a method of monitoring infection amongst murine colonies. Overall, these findings demonstrate that MHV-68 infection can be controlled and monitored in murine research facilities, and the potential for unintentional infection is low.     

Increased neoplasm development due to immunosuppressive treatment with FK-506 in BALB/C mice persistently infected with the mouse herpesvirus (MHV-72).

BALB/c mice were infected with the lymphotropic mouse gammaherpesvirus (MHV-72). At late (7-12 months) post-infection intervals the latent virus was detected in the cells of lymphatic system (peripheral blood, lymphocytes and macrophages, thymocytes, lymph nodes, bone marrow, and peritoneal macrophages,) and in the spleen, lungs, liver, and kidney by cocultivation as well as by explantation. The MHV-72 infected mice, in which latency had been established, were treated with the immunosuppressive (IS) drug FK-506 (2 mg/kg/mouse for 30 days). This treatment increased the probability of virus reactivation by over two-fold. During the post-treatment observation period of 19 months, the incidence of lymphomas and the development of MHV-related lymphoproliferative and hemoblastic disorders raised to nearly five-fold in the drug treated mice as compared to untreated animals.     

Improved Engraftment of Human Spleen Cells in NOD/LtSz-scid/scid Mice as Compared with C.B-17-scid/scid Mice

T and B lymphocyte-deficient mice homozygous for the severe combined immunodeficiency (SCID) mutation can be immunologically engrafted with human lymphocytes. However, low levels of human peripheral blood mononuclear cell engraftment are commonly observed, impeding full use of this model We now demonstrate that strain background in mice homozygous for the scid mutation is a strong determinant of levels of human lymphocyte engraftment. NOD/LtSz-scid/scid mice support higher levels of engraftment of both human spleen and peripheral blood mononuclear cells than do C.B-17-scid/scid mice. We observed, using human spleen cell injected scid mice, 1), high levels of engraftment of the host peripheral lymphoid tissues with human CD45⁺ (leukocytes), CD3⁺ (T cells), CD4⁺ (helper/inducer), and CD8⁺ (suppressor/cytotoxic) lymphoid cells for up to 24 weeks in NOD/LtSz-scid/scid mice; 2), migration of high numbers of human lymphocytes to peripheral lymphoid and nonlymphoid organs in NOD/LtSz-scid/scid, but not in C.B-17-scid/scid mice; 3), higher levels of serum immunoglobulin of human origin in NOD/LtSz-scid/scid mice than in C.B-17-scid/scid mice; 4), histological lesions character-istic of human anti-mouse xenoreactivity in NOD/LtSz-scid/scid mice; and 5), human origin antibodies against filarial antigens after engraftment with naive human spleen cells. The use of NOD/LtSz-scid/scid mice as recipients to achieve significantly enhanced human lymphopoietic cell engraftment will now enable human immunity to be more easily studied in animal models.     

SCID mice show a similar susceptibility to Angiostrongylus cantonensis as do wild-type mice of the C.B-17 strain

C.B-17-SCID/SCID (SCID) mice infected with Angiostrongylus cantonensis yielded a high percentage of worm recovery and did not show any body weight loss until day 24 postinfection. Unexpectedly, C.B-17-+/+ (+/+) mice also produced a similar worm burden containing well-developed worms. This is probably attributable to the observation that +/+ mice failed to induce eosinophilia in cerebrospinal fluid (CSF) despite their production of antigen-specific IgA and IgGl; +/+ mice have defective bone-marrow eosinopoiesis, which in turn results in reduced blood and CSF eosinophilia. Interleukin 5 (IL-5) production in +/+ mice is similar to that in BALB/c and C57BL/6 mice. However, bone-marrow eosinopoiesis in response to IL-5 is markedly suppressed in +/+ mice. This is probably associated with impaired expression of common β-chain mRNA in bone-marrow cells of +/+ mice, which leads to the failure of bone-marrow eosinopoiesis. Hence, +/+ mice may serve as a useful model for the elucidation of eosinophil production in the mouse and for determination of the relationship between parasite infection and the eosinophil. Received: 17 October 1999 / Accepted: 23 December 1999     

Exacerbation of Pneumocystis carinii pneumonia in immunodeficient (scid) mice by concurrent infection with a pneumovirus.

scid mice naturally infected with Pneumocystis carinii and inoculated with a normally apathogenic pneumovirus had significantly higher P. carinii cyst counts and developed significantly more severe P. carinii-related disease than did sham-inoculated, P. carinii-infected scid mice. P. carinii-free, virus-infected scid mice survived for 2 months despite high pulmonary virus titers. These results show that a respiratory virus infection can exacerbate P. carinii disease in an immunocompromised-rodent model.     

Chemokine-binding activities of M3 protein encoded by Murine gammaherpesvirus 72

Murine gammaherpesvirus 68 (MHV-68) contains gene-encoding M3 protein expressed during the acute and persistent phase of infection. This protein features a chemokine-binding activities (Parry et al., 2000; van Berkel et al., 2000). In this study, we demonstrated that the Murine gammaherpesvirus 72 (MHV-72) also contained M3 gene with the codon-changing mutation at the position 920 nt converting amino acid (aa) 307 Asp (GAC) to Gly (GGC). The mutation in the M3 protein was localized near chemokine-binding domain and was able to change the secondary structure of M3 protein. We examined the binding activities of M3 proteins of MHV-72 and MHV-68 to five human chemokines (CCL3, CCL5, CCL11, CCL2, and CXCL8). Binding activity of MHV-72 M3 protein to CCL5 as well as to CXCL8 reached only 11.1% (day 3 p.i.) to 20% (day 4 p.i.) of the activity detected for MHV-68 M3 protein. On the other hand, MHV-72 M3 protein bound to human cytokines CCL11 and CCL2 reached about 90% of the binding detected for MHV-68 M3 protein. The binding activity of both M3 proteins to human CCL3 was similar. These data implied that mutation identified in MHV-72 M3 protein might be involved in attenuation of immune response to infection with MHV-72. Key words: murine gammaherpesvirus; chemokine-binding protein; M3 protein.     

Comparison of polymerase chain reaction and culture for detection of Borrelia burgdorferi in naturally infected Peromyscus leucopus and experimentally infected C.B-17 scid/scid mice.

Culture and the polymerase chain reaction (PCR) were compared for detection of Borrelia burgdorferi infection in wild-caught Peromyscus leucopus and experimentally inoculated C.B-17 scid/scid (severe combined immunodeficient) mice. PCR targeted highly conserved regions of the ospA gene and could detect one to five cultured organisms and 10 to 50 copies of molecularly cloned ospA DNA. Organs (kidney, spleen, and urinary bladder) and/or ear biopsy samples were obtained from 108 captured P. leucopus mice, and tissues were obtained from 7 experimentally inoculated mice. A simple sample-processing procedure with proteinase K and detergent treatment was used in the PCR analysis. Overall, B. burgdorferi was detected in 29 of 108 (27%) P. leucopus mice by culture and in 31 of 108 (29%) mice by PCR. As assessed by the kappa statistic, agreement between PCR and culture was high for ear and bladder (kappa = 0.80 and 0.65, respectively) and low for kidney and spleen (kappa = 0.37 and 0.03, respectively). While concordant results were obtained from 98 animals, PCR detected B. burgdorferi from 6 additional mice for which cultures were negative and culture detected B. burgdorferi from 4 animals which were PCR negative. Further phenol-chloroform extraction of DNA in a limited number of samples improved the sensitivity of PCR compared with that of culture. These results indicate that PCR may be as sensitive as culture for detecting B. burgdorferi in ear samples and that PCR analysis is suitable for establishing the infection status of animals in mark-release-recapture studies.     

Molecular genotyping of the mouse scid allele.

Severe combined immunodeficiency (SCID) mice, which lack mature B- and T-cells, provide an important system for studies on immunity and disease. However, since the scid mutation is a single T-to-A transversion, genotypic analysis can be problematic. We have developed a rapid and simple sequence-based analysis that provides identification of both the scid and the wild-type (+) allele. This allows unequivocal identification of scid/scid, scid/+ and +/+ individuals. The method is of greatest utility for discerning scid/+ from +/+ animals during genetic complementation studies, but may be of value for routine SCID colony control as well.     

Regulation of maternal-fetal virus transmission in immunologically reconstituted SCID mice infected with lactate dehydrogenase-elevating virus.

Immunodeficient SCID (C.B-17 scid/scid) mice with persistent lactate dehydrogenase-elevating virus (LDV) infection failed to produce IgG anti-LDV antibodies, and during chronic infection transmitted virus infection to 95% of their offspring. In contrast, normal mice infected 15 or more days prior to giving birth produced IgG anti-LDV antibodies and transmitted LDV infection to only 0-46% of their fetuses. Transplacental transmission of LDV infection was dependent on the timing of maternal infection. Adoptive transfer of immune competence to LDV-infected SCID mice resulted in fetal protection from maternally transmitted virus infection. Fetal protection correlated with the presence of maternal IgG anti-LDV but not with fetal levels of IgG anti-LDV, and the levels of viremia in nonimmune SCID mice did not affect transplacental virus transmission. These results demonstrate the importance of maternal immunity in protecting the fetus from infection, and validate the use of this mouse model for investigation of immune mechanisms of transplacental virus transmission.     

Response of scid mice to establishment of Leishmania major infection.

The initiation of Leishmania major infection in susceptible BALB/c mice is regulated by interferon-gamma (IFN-gamma). To examine further the mechanisms of IFN-gamma-dependent regulation of the establishment of L. major, we studied the characteristics of the infection in severe combined immunodeficient (scid) mice. In the first 2 weeks of infection, we observed a delay in the development of the lesions in the footpads and lower numbers of parasites in scid compared with BALB/c mice. By week 5 after infection, the size of the leishmanial lesion was similar in both strains of mice, but the number of parasites in scid mice was 100-fold higher than in BALB/c. Treatment with anti-IFN-gamma during the establishment of L. major did not alter the course of infection in scid mice, while it exacerbated lesion development in BALB/c mice. Macrophages from scid mice were unable to kill L. major when stimulated with IFN-gamma in vitro, and produced lower levels of nitric oxide compared with macrophages from susceptible BALB/c or the resistant C57Bl/6 mice. We examined whether delayed lesion development in scid mice was due to their inability to mount appropriate inflammatory responses. While significantly fewer nucleated cells were present in the footpads of scid mice compared with BALB/c, 2 and 3 weeks after infection, no difference in inflammatory response between scid and BALB/c mice was observed in response to L. major antigen in the footpads. In contrast, there was a dramatic increase in the number of cells in the popliteal lymph nodes of BALB/c mice. Decreased inflammatory responses of scid mice in the footpad (at the site of infection) may contribute to slower development of leishmanial lesions during the first 2 weeks of infection.