Thymocyte-dependent immunity to toxoplasmosis in the normal and immunocompromised guinea-pig host

An epidemic of toxoplasmosis in a captive colony of squirrel monkeys (Saimiri sciureus)

An epidemic of acute, disseminated toxoplasmosis caused 30 per cent mortality and an apparent 100 per cent morbidity in a captive colony of squirrel monkeys (Saimiri sciureus). The source of the infection could not be elucidated. Although most deaths were due to pulmonary oedema, one monkey probably died of heart and liver failure. These findings support the view that New World monkeys are unusually sensitive to Toxoplasma gondii infection. The similarity of the disease in these monkeys with that in immunocompromised human beings is an observation worthy of further investigation.

Passive immunization protects guinea pigs from lethal Toxoplasma infection

The cellular and humoral interactions that contribute to protective immunity in toxoplasmosis were studied by adoptive transfer of selective cell populations or immune serum and its fractions into normal syngeneic strain 2 guinea pigs. The results of this study with the RH strain of Toxoplasma gondii confirm and extend the findings of previous studies by showing that the passive transfer of parasite-sensitized T cells or of immune serum from previously infected donors protected recipient guinea pigs against lethal toxoplasmosis. An additional key finding was that similar levels of complete protection against lethal infection occurred in guinea pigs receiving partially purified anti-Toxoplasma immunoglobulins or immune cells that had been enriched for B cells prior to transfer. Cells residing in the spleen, lymph nodes and peritoneal cavity, but not the thymus, were equally effective in conferring immunity to challenged recipients. In addition, cell titration experiments revealed that guinea pigs could survive T. gondii infection by infusing them with as little as 2 x 10(7) sensitized T cells or B cells. Unlike protection mediated by T cells, protection against lethal disease occurring in the B cell recipients was associated with the formation of Toxoplasma antibodies. These findings illustrate the major role of both humoral and cell-mediated immunity in affording protection against toxoplasmosis based on a guinea pig model of the human disease.

CD8+ T cells are the major lymphocyte subpopulation involved in the protective immune response to Toxoplasma gondii in mice

The ability of the major T cell subsets to adoptively transfer resistance to T. gondii infection was studied. Spleen cells harvested from mice with a 3-month T. gondii infection and cells from uninfected mice were enriched for T cells by nylon/wool purification. Adoptive transfer of these cells from both groups of donor mice led to a significant increase in the survival of syngeneic recipient mice infected intraperitoneally with 20 T. gondii cysts. Increased survival was mediated particularly by CD4-depleted but also, to a lesser extent, CD8-depleted subpopulations. These results were confirmed in T cell reconstituted athymic nude mice. Unfractionated T cells from chronically infected donors produced a significant inhibition of cyst formation in the brains of recipient mice measured 10 weeks after infection compared with control mice. The inhibition of cyst formation was ablated by pretreating T cells with anti-CD8 antibody and complement, but not anti-CD4 antibody and complement. Mice receiving cells from infected donors produced an early increase in their IgG1 and IgG2a antibody titres compared with mice given cells from uninfected animals. The depletion of either CD8+ or CD4+ immune cells appeared to have little effect on the antibody responses in recipient mice and there was no correlation between antibody levels and immunity. The results indicate that CD8+ T lymphocytes from convalescent T. gondii-infected BALB/c mice are the principal mediators of resistance to T. gondii, although CD4+ T cells appear to be involved during the acute phase of infection.

Monoclonal antibodies identify new Toxoplasma gondii soluble antigens

In order to characterize Toxoplasma gondii antigens, we have produced a panel of monoclonal antibodies specific for the parasite. A total of 22 hybridomas were derived from the spleen cells of mice immunized either with a 100,000 g supernatant of a sonicate from the RH strain (called F3), or chronically infected with the Wiktor or the 76K strain. Except for one hybridoma producing an IgM, all the hybridomas derived from mice immunized with F3 produced IgG1 antibodies while those obtained from chronically infected mice produced antibodies belonging to the IgG2b, IgG2a and IgM subclasses. Western-blot analysis showed that the panel of monoclonal antibodies defines at least 7 distinct antigens or antigen families. An antigen of apparent Mw 25 kD present exclusively in the 100,000 g supernatant of the T. gondii sonicate was recognized by the majority of monoclonal antibodies derived from mice immunized with the F3 fraction. Two other antigens of apparent Mw 27 kD and 29 kD present in the soluble and insoluble fractions of the sonicate were also identified. Monoclonal antibodies against the previously described 21 kD and 31 kD surface antigens and belonging to the IgG2a but also to the IgG1 subclasses were able to mediate lysis of the parasite in the presence of human non immune serum. The 22 monoclonal antibodies did not identify antigenic differences between the two independently isolated RH and Wiktor strains.

Isolation of Borrelia burgdorferi from the blood of seven patients with Lyme disease

PURPOSE

Borrelia burgdorferi, the etiologic agent of Lyme disease, has rarely been successfully cultured from blood. We report on seven patients from Westchester County, New York, with B. burgdorferi bacteremia diagnosed between April 1987 and August 1987.

PATIENTS AND METHODS

One hundred thirty-two attempts to isolate spirochetes were made on blood specimens obtained from 104 patients. Twenty-two of these specimens were obtained from nine patients who had recently been bitten by Ixodes ticks but who were asymptomatic. Heparinized blood or serum specimens (0.2 to 0.4 mL) were inoculated onto 6 mL of modified Barbour-Stoenner-Kelly medium. Lyme serology was performed by enzyme-linked immunosorbent polyvalent, IgM, and IgG assays, fluorescent immunoassay, and microhemagglutination.

RESULTS

Four of the seven patients had erythema migrans, two had facial nerve palsy, and one had a flu-like syndrome without rash. These patients represented 21% (four of 19) of all patients with the characteristic skin lesion who had blood cultures for B. burgdorferi, and 40% (two of five) of all those with facial nerve palsy. Serologic testing was frequently nonreactive; two patients had no detectable antibody on multiple sera by five different assays. All patients improved with antibiotic treatment, and had negative subsequent blood cultures, but five of seven had persistent complaints after completion of therapy.

CONCLUSION

Culturing blood for B. burgdorferi may be useful in confirming the diagnosis of Lyme disease in selected patients. Use of spirochete blood cultures may facilitate a better understanding of the pathogenesis and natural history of Lyme disease.

Trial of a novel experimental Toxoplasma iscom vaccine in pregnant sheep

Fifteen vaccinated ewes (group 1) and 13 unvaccinated ewes (group 2) were each challenged orally with 2000 sporulated Toxoplasma gondii oocysts at 91 (+/- 1) days' gestation. Another four pregnant ewes acted as unvaccinated unchallenged controls. Lamb mortality in group 1 was 36.4% after a mean gestation of 141 days while in group 2 it was 64.7% after a mean gestation of 131.5 days. These differences were not statistically significant. However, substantially more specific antibody was detected in precolostral sera from live lambs from vaccinated ewes than in live lambs from unvaccinated ewes in group 2.