The intracellular protozoan Toxoplasma gondii is a widespread opportunistic parasite of humans and animals. Normally, T. gondii establishes itself within brain and skeletal muscle tissues, persisting for the life of the host. Initiating and sustaining strong T-cell-mediated immunity is crucial in preventing the emergence of T. gondii as a serious pathogen. The parasite induces high levels of gamma interferon (IFN-γ) during initial infection as a result of early T-cell as well as natural killer (NK) cell activation. Induction of interleukin-12 by macrophages is a major mechanism driving early IFN-γ synthesis. The latter cytokine, in addition to promoting the differentiation of Th1 effectors, is important in macrophage activation and acquisition of microbicidal functions, such as nitric oxide release. During chronic infection, parasite-specific T lymphocytes release high levels of IFN-γ, which is required to prevent cyst reactivation. T-cell-mediated cytolytic activity against infected cells, while easily demonstrable, plays a secondary role to inflammatory cytokine production. While part of the clinical manifestations of toxoplasmosis results from direct tissue destruction by the parasite, inflammatory cytokine-mediated immunopathologic changes may also contribute to disease progression.

https://cmr.asm.org/content/cmr/11/4/569.full.pdf

Regulation and Function of T-Cell-Mediated Immunity during Toxoplasma gondii Infection

Fish-borne parasitic zoonoses: Status and issues

Cytotoxic T lymphocytes (CTL) are thought to control hepatitis B virus (HBV) infection, since they are readily detectable in patients who clear the virus whereas they are hard to detect during chronic HBV infection. In chronic hepatitis C virus (HCV) infection, however, the virus persists in the face of a CTL response. Indeed, most infected patients respond to one or more HCV-1 (genotype 1a)-derived CTL epitopes in the core, NS3, and NS4 proteins, and the CTL response is equally strong in patients infected by different HCV genotypes, suggesting broad cross-reactivity. To examine the effect of the HCV-specific CTL response in patients with chronic hepatitis C on viral load and disease activity, we quantitated the strength of the multispecific CTL response against 10 independent epitopes within the HCV polyprotein. We could not detect a linear correlation between the CTL response and viral load or disease activity in these patients. However, the CTL response was stronger in the subgroup of patients whose HCV RNA was below the detection threshold of the HCV branched- chain DNA assay than in branched-chain-DNA-positive patients. These results suggest that the HCV-specific CTL response may be able to control viral load to some extent in chronically infected patients, and they indicate that prospective studies in acutely infected patients who successfully clear HCV should be performed to more precisely define the relationship between CTL responsiveness, viral clearance, and disease severity in this infection.

Differential cytotoxic T-lymphocyte responsiveness to the hepatitis B and C viruses in chronically infected patients.

The Biology and Evolution of Trematodes

Oral-route infection with Toxoplasma gondii sporozoites or tachyzoites leads to the rapid spread of quick-replicating cytolytic tachyzoites throughout the whole body. Toxoplasma easily crosses the blood-retina, encephalic and placental barriers. The acute phase of this infection lasts for less than around ten days. The parasite causes a very strong type-1 response focused on the interferon-gamma secreted by the T lymphocytes. This immune response limits the tissue extension of the parasite, ensuring the survival of the host, but, paradoxically, also aiding the survival of the parasite by converting it into a bradyzoite, an intracellular quiescent resistant form persisting in the muscle and brain tissues.

Immune response to Toxoplasma gondii.

Cytotoxic cells specific for Toxoplasma gondii-infected cells were detected in the peripheral blood leukocytes from a patient with acute toxoplasmosis. The cytotoxicity was mediated by CD5+, CD4-, CD8+ cells. The cytotoxic T cells lysed Toxoplasma-infected target cells with HLA class I restriction. Two types of T cell clones were established from peripheral blood leukocytes of a patient with chronic toxoplasmosis; one was a CD5+, CD4-, CD8+ cytotoxic cell specific for Toxoplasma-infected cells, and the other was a CD5+, CD4+, CD8- proliferative cell that responded to Toxoplasma antigen. Toxoplasma-infected cell-specific cytotoxic cloned T cells recognize the infected target cells in the context of the HLA class I molecules, and the CD8 molecule was involved in the cytotoxicity. Toxoplasma antigen-specific proliferative cloned T cells were stimulated by Toxoplasma antigen-pulsed or Toxoplasma-infected cells in conjunction with HLA-DR molecule on the target cells. Thus, antigen presentation by Toxoplasma-infected cells for activation of both cytotoxic and proliferative T cells has been demonstrated.

Antigen presentation by Toxoplasma gondii-infected cells to CD4+ proliferative T cells and CD8+ cytotoxic cells.

The eggs of Trichuris, detected in the feces of 19 persons who had stayed in institutions for mentally retarded and/or multi-handicapped patients, were identified as those of T. vulpis (Froelich, 1789) on the basis of morphological features. This is the first record of human infection with the canine whipworm in Japan.

Human cases of infection with canine whipworms, Trichuris vulpis (Froelich, 1789), in Japan.

Unresponsiveness of antigen-dependent (Toxoplasma-specific and purified protein derivative of tuberculin (PPD)-specific) T-cell proliferative responses of peripheral blood leukocytes (PBL) was observed in a patient with symptomatic acute toxoplasmosis. The immunosuppression of T-cell responses was mediated by Leu +, Leu 2a+, and Leu 3a- suppressor T cells that were induced by Toxoplasma gondii antigen and suppressed both Toxoplasma-specific and PPD-specific PBL T-cell responses from a patient with chronic toxoplasmosis when PBL of these patients were mixed and cocultured in vitro. Participation of class II molecules of HLA in Toxoplasma-specific proliferative T-cell responses and activation of suppressor T cells was examined by using monoclonal antibodies specific for HLA-DR and HLA-DQ molecules. Anti-HLA-DQ monoclonal antibody released the suppressive activity, while anti-HLA-DR monoclonal antibody inhibited Toxoplasma-specific T-cell responses. Thus, the suppressive effect of PBL from a patient with acute toxoplasmosis on antigen-dependent PBL T-cell responses from a patient with chronic toxoplasmosis was mediated by HLA-DQ molecules. By contrast, Toxoplasma-specific T-cell responses were activated by HLA-DR molecules (presumably present on

https://www.jstor.org/stable/info/3282518

Immune response to Toxoplasma gondii--analysis of suppressor T cells in a patient with symptomatic acute toxoplasmosis.

Newly laid eggs of Schistosoma japonicum were cultured in a serum-free, chemically defined me- dium, RPMI 1640, which contained 20 amino acids, glutathione, 11 vitamins, and glucose in a balanced salt solution. The requirements for these components in the nutrition of the eggs was investigated by the deletion of single component from the medium. The following 14 amino acids were shown to be essential for the full development of the egg in the medium: L-arginine, L-cystine, glycine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-serine, L-threonine, L-tryptophan, L-tyrosine, and L-valine. Choline chloride was the essential vitamin. The omission ofnicotinamide from the medium affected maturation adversely. Glucose was also required by the eggs. Minimal concentration of glucose for maturation of the eggs was 0.02 mM, but concentrations ranging from 0.16 to 20.00 mM gave better results while the concentration of the other elements of the medium were kept constant. Eggs of Schistosoma japonicum are laid in an unembryonated state in the mesenteric veins of the mammalian host. The newly deposited eggs require 9 or 10 days to reach the miracidial stage in vivo (Vogel, 1942). Because the egg is the prime inducer of schistosomal pathology, knowl- edge of the metabolism of the egg is important for chemotherapy, diagnosis, and control of these parasites. It is known that the egg shell is porous (Stenger et al., 1967; Race et al., 1969; Demaree and Hillyer, 1981), and that the egg secretes en-

Nutritional requirements of Schistosoma japonicum eggs.

In schistosomiasis japonica, eggs of the schistosome play a predominant role in its pathology (Warren, 1978, Nature 273: 609-612). Therefore, knowledge of the metabolism of the eggs is essential for better understanding of pathogenesis. The eggs are deposited within the mesenteric blood vessels in an unembryonated state and embryonate in the tissue of the mammalian host (Vogel, 1942, Dtsch. Trop. Z. 46: 57-69, 81-91). Cultivation of the schistosome egg from a single egg cell into a miracidium in a chemically defined medium is a prerequisite for strict investigation of its metabolism. In order to improve or simplify the composition of culture media for schistosome eggs, it is important to know the nutritional requirements of the eggs. We previously reported that the eggs require 14 L-amino acids (arginine, cystine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, serine, threonine, tryptophan, tyrosine, and valine), two vitamins (choline chloride and nicotinamide), and glucose for full development (Kawanaka et al., 1983, J. Parasitol. 69: 857). These essential nutrients had been determined by the deletion of single components from Medium RPMI 1640 that supports development of the eggs and contains 20 amino acids, glutathione, 11 vitamins, and glucose in a balanced salt solution. However, in the medium composed of all these essential 14 amino acids, two vitamins, glucose, and electrolytes, S. japonicum eggs did not mature. The electrolytes were those in Earle's balanced salt solution. This medium was tentatively designated as the basic one and the minimum necessary supplement to the basic medium was searched for among six amino acids, the remaining amino acid components in Medium RPMI 1640. The six amino acids tested were asparagine, aspartic acid, proline, hydroxyproline, glutamic acid, and glutamine. Here we report that glutamine is an essential and sufficient supplement to the basic medium. Preparation of the minimum essential medium for cultivation of Schistosoma japonicum eggs is presented. Adult schistosomes (8 wk old) were recovered under aseptic condition from the dd strain of mice that had been infected intraperitoneally with 50 cercariae of a Japanese strain of Schistosoma japonicum. Techniques relating to the collection of newly laid eggs of schistosome and their subsequent maintenance in culture have been described, as have the method for the assessment of maturation of the eggs (Kawanaka et al., loc. cit.). The concentrations of amino acids, vitamins, and glucose in test media for the present experiment are the same as those in Medium RPMI 1640. Table I shows results of the addition of supplementary amino acids alone or in combination to the basic medium in Earle's balanced salt solution. The single addition of asparagine, aspartic acid, proline, hydroxyproline, or glutamic acid elicited no effect on the development of eggs.

Shigeo Hayashi

Papers

Antigen presentation by Toxoplasma gondii-infected cells to CD4+ proliferative T cells and CD8+ cytotoxic cells.

Human cases of infection with canine whipworms, Trichuris vulpis (Froelich, 1789), in Japan.

Immune response to Toxoplasma gondii--analysis of suppressor T cells in a patient with symptomatic acute toxoplasmosis.

Nutritional requirements of Schistosoma japonicum eggs.

A minimum essential medium for cultivation of Schistosoma japonicum eggs.