Imtiaz A. Khan

IL‐10 mediates immunosuppression following primary infection with Toxoplasma gondii in mice

Suppression of the host immune response by Toxoplasma gondii has been observed in both human and experimental murine infection. In this study, inbred mice were infected with T. gondii. At day 7 post‐infection, the lymphoproli‐ferative response to both mitogen and superantigen as well as parasite antigen were found to be significantly depressed. Using a transwell system, it was determined that the reduced proliferative response was due to soluble factor (s) being expressed by splenocytes from the infected mice. Isolation of the splenocytes into an adherent and nonadherent population suggested that both macrophages and T cells were able to produce at least one soluble factor. Tissue culture supernatant derived from the splenocytes of the infected mice contain increased levels of IL‐10, whereas measurable IL‐2 levels could not be quantitated. At day 7 post‐infection, both a biologic assay for IFN‐γ in culture supernatant and the expression of IFN‐γ mRNA in the splenocytes were reduced. Antibody to IL‐10 was able to partially neutralize (almost 50%) the in vitro immune downregulation of the tissue culture supernatant. Anti‐IL‐10 in combination with a nitric oxide (NO) antagonist was able to reverse the inhibitory activity of the culture supernatant by 85%. Since IL‐10 is a potent antagonist of IFN‐γ, it may represent a critical cytokine involved in mediating T. gondii induced immunosuppression in the infected host.

Immune response to Encephalitozoon cuniculi infection

Microsporidia are obligate intracellular parasites, which can cause complications in immunocompromised individuals. Very little is known about the host immune response generated against these infectious agents. Encephalitozoon cuniculi is the best studied microsporidian and the protective immune response against this parasite is mediated by cytotoxic CD8(+) T cells.

Lack of CD4+ T Cells Does Not Affect Induction of CD8+ T-Cell Immunity against Encephalitozoon cuniculi Infection

ABSTRACT Cell-mediated immunity has been reported to play an important role in defense against Encephalitozoon cuniculi infection. Previous studies from our laboratory have underlined the importance of cytotoxic CD8+ T lymphocytes (CTL) in survival of mice infected with E. cuniculi. In the present study, immune response against E. cuniculi infection in CD4+T-cell-deficient mice was evaluated. Similar to resistant wild-type animals, CD4−/− mice were able to resolve E. cuniculi infection even at a very high challenge dose (5 × 107 spores/mouse). Tissues from infected CD4−/− mice did not exhibit higher parasite loads in comparison to the parental wild-type mice. Conversely, at day 21 postinfection, susceptible CD8−/− mice had 1014 times more parasites in the liver compared to control wild-type mice. Induction of the CD8+ T-cell response in CD4−/− mice against E. cuniculi infection was studied. Interestingly, a normal antigen-specific CD8+T-cell response to E. cuniculi infection was observed in CD4−/− mice (precursor proliferation frequency, 1/2.5 × 104 versus 1/104 in wild-type controls). Lack of CD4+ T cells did not alter the magnitude of the antigen-specific CTL response (precursor CTL frequency; 1/1.4 × 104 in CD4−/− mice versus 1/3 × 104 in control mice). Adoptive transfer of immune CD8+ T cells from both CD4−/− and wild-type animals prevented the mortality in CD8−/− mice.E. cuniculi infection thus offers an example of an intracellular parasitic infection where CD8+ T-cell immunity can be induced in the absence of CD4+ T cells.

Role of P30 in Attachment and Immunity to T. Gondii

Because of its adaptability to the laboratory, most work has focused on the tachyzoite stage of T. gondii. [reviewed in Kasper et al., 1992]. Of the several antigens recognized by the immune sera Ig fraction, the most prevalent has a Mr of 30Kd. Most work to date on the various toxoplasma antigens has concentrated on either the 30Kd (P30) or 22Kd (P22) proteins. Of the two, P30 is the major iodinated protein on a number of geographically diverse human and animal isolates of toxoplasma [Ware and Kasper, 1987]. Analysis of the gene encoding the P30 molecule show it to be highly conserved with only an 8 amino acid variation among tested strains. The P30 gene is single- copy and contains no introns [Burg et al, 1988]. This molecule comprises 3–5% of the total parasite protein and is a major component of the vesicular network within the parasitophorous vacuole [Sibley et al, 1986]. Intact intra- and extracellular parasites show a homogeneous distribution of P30; however, upon invasion of the host cell, most of the monoclonal antibody against P30 is shed from the tachyzoite [Dubremetz et al, 1985]. Mono- and polyclonal antibody against P30 is parasiticidal to extracellular T. gondii in the presence of serum complement [Kasper et al, 1987]. By competition binding assay, a single monoclonal directed against P30 can inhibit 25–30% of the specific binding of human immune serum to toxoplasma, sugesting that P30 is the most immunogenic constituent of the tachyzoite and that a single region of this molecule may contain most of the immunogenic activity.