An avirulent lipophosphoglycan-deficient Leishmania major clone induces CD4+ T cells which protect susceptible BALB/c mice against infection with virulent L. major.

An avirulent clone of Leishmania major was used to immunize susceptible BALB/c mice against challenge with virulent L. major. By using the immunized animals as a source of cells, CD4+ parasite-specific T-cell lines could be generated in vitro which, when adoptively transferred to naive BALB/c recipients, conferred marked protection against challenge with virulent L. major. Compared with CD4+ parasite-specific T-cell lines generated from nonimmunized BALB/c mice infected with L. major, the protective T-cell lines generated from immunized mice produced substantially less interleukin-4 and substantially more tumor necrosis factor and interleukin-2. Interestingly, the protective CD4+ T cells did not mediate L. major-specific delayed-type hypersensitivity in vivo and proliferated in vitro only in response to living L. major and not to frozen-and-thawed antigen preparations of the parasite. Finally, the avirulent clone of L. major was found to express the major surface glycolipid of L. major, lipophosphoglycan, at a level that was sixfold less than expression of this molecule by virulent L. major. In addition, lipophosphoglycan of the avirulent parasite failed to mature into the larger, or metacyclic, form of the molecule.

Methyl prednisolone acetate modulation of infection and subsequent pulmonary pathology in hamsters exposed to parainfluenza-1 virus (Sendai).

Parainfluenza-1 virus (PI-1) has a wide host range; the disease process observed varies with the age, previous exposure, and species. This study was performed to determine possible effects of the corticosteroid methyl prednisolone acetate (MPA) on PI-1 infection in hamsters. Hamsters serologically negative for PI-1 were exposed to virus alone or were exposed to virus the day after pretreatment with a single subcutaneous injection of MPA. Serum antibodies to PI-1 were present in virus-only exposed hamsters by Day 8 and increased up to Day 20. PI-1 was recovered from lungs of virus-only exposed hamsters on Day 2 to 8. Virus antigen was detected by immunocytochemistry on Days 2 to 10 in lungs of virus-only exposed hamsters. Virus-associated lesions in these hamsters began as acute bronchiolar epithelium degeneration and necrosis on Day 4 and were foci of fibrosis by Days 12 to 20. Hamsters exposed to virus after MPA treatment developed no antibodies to virus, had no virus detectable by plaque assays or immunocytochemistry, and had no pulmonary lesions. Hamsters treated with MPA had decreased total lymphocyte counts up to Day 20 after treatment. Treatment of hamsters with MPA one day prior to PI-1 virus exposure is associated with no detectable evidence of viral infection. Humoral and cellular immunity mediated by MPA-sensitive lymphocytes may mediate some of the manifestations of PI-1 pulmonary disease.

Pathogenicity of fibroblast- and lymphocyte-specific variants of minute virus of mice.

We tested two strains of the minute virus of mice (MVM) for pathogenic effects and patterns of infection in laboratory mice. The two strains differ in their ability to infect differentiated cultured cells: the prototype virus, MVMp, infects only fibroblasts, while its variant, MVMi, is restricted to lymphocytes. We find that neither strain has any demonstrable effects on the T-cell function of mice infected as adults. In contrast, MVMi, but not MVMp, is able to induce a runting syndrome accompanied by mild immune deficiencies upon the infection of newborn mice. After neonatal infection, MVMi spreads to many organs, and the presence of viral replicative form DNA is evident in nucleic acid hybridization experiments. In contrast, replication of MVMp can be detected only by the seroconversion of infected animals. Newborn mice that grow abnormally as a result of MVMi infection also have low circulating antibody titers to the virus. This phenomenon may be a consequence of the lymphotropism of MVMi.

Studies on the pathogenesis of epizootic bovine abortion.

Ornithodoros coriaceus Koch ticks were fed on 37 pregnant cows. The fetuses were obtained from the cows at 23 to 126 days after maternal tick exposure. Characteristic lesions of epizootic bovine abortion were observed only in those fetuses recovered 100 days more or after maternal tick exposure. Fetuses collected between 50 and 100 days showed mild-to-moderate lymphoid and mononuclear cell hyperplasia. Reaction in fetuses studied less than 50 days after maternal tick exposure were mild. Lesions could not be seen in 2 of the youngest fetuses. Increases in serum immunoglobulin concentrations were present only in those fetuses examined 80 days or more after their dams had been exposed to ticks. The specificity of the immunoglobulins could not be determined. Sera from 12 fetuses tested failed to fix complement in tests for group-specific chlamydial antibodies. A wide variety of microbiological cultivation attempts were made to recover the causative agent of epizootic bovine abortion from these fetuses; however, no agent was recovered regularly, and chlamydial organisms were not recovered from any. The significance of 2 recovered agents, apparently viral, is still to be determined. Fetal tissues, both frozen and fresh, collected from fetuses of dams exposed to a feeding of ticks were capable of reproducing the disease after inoculation into pregnant cows or directly into fetuses.

Epizootic bovine abortion: histogenesis of the fetal lesions.

The development of the fetal lesions of epizootic bovine abortion (EBA) was studied in a series of experiments and field cases of the disease. Thirty-six experimentally infected fetuses were recovered at periods of 29 to 126 days after their dams had been infected by allowing the vector tick Ornithodorus coriaceus to feed on them. The sequential development of the fetal lesions was studied and the lesions compared with those in both naturally occurring and experimentally induced infections of the dams which either aborted or carried to term. The early changes observed in the fetuses consisted of transformation and proliferation of lymphocytes and mononuclear phagocytes. These changes were marked by 50 days after tick exposure of the dams, but fetal lesions specific enough to permit making the diagnosis of the disease did not develop until 100 days after dams were exposed by tick feeding. In the fetuses which were either aborted or carried to term after prolonged infection, acute necrotizing lesions were superimposed on the chronic proliferative fetuses. Acute necrotizing foci developed in several organs, but most commonly in lymph nodes and spleen. These foci frequently formed pyogranulomas. Acute vasculitis developed at the same time as the acute focal-necrotizing lesions. These lesions were similar to immune-mediated lesions that result from the deposition of toxic complexes in the tissues. Immunofluorescent examination demonstrated that immunoglobulins (Ig)G and IgM were present in the vascular lesions.