Trichinella spiralis: changes caused in the mouse's thymic, splenic, and lymph node cell populations

Thymus atrophy and double-positive escape are common features in infectious diseases

The thymus is a primary lymphoid organ in which bone marrow-derived T-cell precursors undergo differentiation, leading to migration of positively selected thymocytes to the T-cell-dependent areas of secondary lymphoid organs. This organ can undergo atrophy, caused by several endogenous and exogenous factors such as ageing, hormone fluctuations, and infectious agents. This paper will focus on emerging data on the thymic atrophy caused by infectious agents. We present data on the dynamics of thymus lymphocytes during acute Trypanosoma cruzi infection, showing that the resulting thymus atrophy comprises the abnormal release of thymic-derived T cells and may have an impact on host immune response.

Biological and immunological characteristics of Trichinella pseudospiralis

In 1972 three new species were proposed for the genus Trichinella, which for 137 years had contained a single species, Trichinella spiralis (Owen,1835). One of these proposed species, Trichinella pseudospiralis, was markedly different from the others in that it was smaller in size, the muscle-stage larvae were not surrounded by a capsule, and it was capable of parasitizing birds. Owing to a lack of information on the normal host range, geographic distribution, biochemistry, immunology and normal variation in biological characteristics of these organisms, several authors supported the more conservative position of designating them sibling species, subspecies or races of Trichinella. The summary statement following the session on Parasite Genetics and Speciation at the 7th International Conference on Trichinellosis recommended that pseudospiralis be accepted as a new species of Trichinella. In this article George Stewart reviews the available information on the biological and immunological characteristics of T. pseudospiralis.

Metabolic integration during the host associations of multicellular animal endoparasites

The nature of metabolic interaction during parasitic infection was discussed and the concept of metabolic integration outlined. The subjective nature of the integrative argument was noted. The parasite-host relationships of larval trematodes of the genus Schistosoma with their intermediate molluscan hosts, the nematode Trichnella spiralis and cestode Hymenolepis diminuta, with their definitive hosts, as well as the hymenopterous insect parasite, Hyposoter exiguae, with its insect host, Trichoplusia ni, were examined. The significance of the immune system in the establishment of the parasite-host association and the means by which parasites evade host defense were discussed. The involvement of microorganisms or "hyperparasites" during the host associations of multicellular parasites was described. The importance of evolutionary considerations in assessing the nature of metabolic interaction and its significance to the success of the parasite-host relationship was emphasized. The use of teleological assessment and anthropomorphic description was discussed.

Immunomodulation by Propionibacterium granulosum KP 45 and experimental trichinellosis in mice

Swiss mice were infected orally with 200 Trichinella spiralis larvae and injected intraperitoneally with a potent immunomodulator (isolated cell walls of Propionibacterium granulosum strain KP 45). In control mice 22 871 +/- 9913 larvae were found in the whole body, whereas in mice treated with P. granulosum KP 45 on the day of inoculation 9450 larvae +/- 8244 larvae were counted (p less than 0.01). Immunomodulation 7 days before or 7 days after T. spiralis inoculation gave less pronounced effects but the decreasing number of larvae was still significant. It is suggested that the above effects are due to an activation of macrophages.

Trichinella spiralis: selective intestinal immune deviation in the rat

In rats, infections with 100-2000 Trichinella spiralis muscle larvae lead to a prompt immunity that is expressed in parasite expulsion within 14 days. Rats infected with more than 2000 larvae display impaired immunity with rejection delayed by 50% (7 days) or more. Suppression is selective for expulsive immunity as the antifecundity response of rats is directly proportional to dose and is expressed sooner in heavily infected subjects. Suppression of intestinal expulsive immunity was suggested by the fact that, with low doses (2000 larvae or less), worm rejection was inhibited by cortisone, whereas cortisone inhibited antifecundity but had no discernable effect on worm rejection in high-dose infections. Evidence for local immune deviation as opposed to systemic immunosuppression was obtained in experiments using parabiotic rats. When one partner was infected with 6000 worms and the other with 200, the rat infected with 200 parasites showed earlier rejection than was seen in single controls infected with 200 worms. The prolonged survival of high-dose adults was not accompanied by a change in the site of worm residence in the gut. Immunological parameters such as serum antibody levels, the number of activated cells or specific anti-T. spiralis lymphocytes in thoracic duct lymph were all increased in a dose-dependent manner. These experiments therefore demonstrate a novel autoprotective mechanism by which adult T. spiralis selectively reduce the expression of expulsive immunity in the gut.

[Dynamics of splenic lymphocytes and immunosuppression in Toxoplasma infected mice (author's transl)]

Mice infected with high-virulent strains of T. gondii sustained a marked decrease of splenic lymphocytes within 7-10 days after infection, just prior to death. When infected with a low-virulent strain, the numbers of splenic lymphocytes and of T-lymphocytes fluctuated, but gradually increased over a period of 30 days. To evaluate their immunologic potential, the mice infected with a low-virulent strain of Toxoplasma were immunized with sheep erythrocytes on different days after infection, and antibody levels were measured by direct hemagglutination. Antibody response was minimal when sheep cells had been injected 10 days after infection with Toxoplasma; subsequently immunologic reactivity improved, but even after 30 days anti-sheep agglutinin titers were still below pre-infection levels.