Effect of Toxoplasma gondii on the Thymus

Low dose aerosol infection of mice with virulent type A Francisella tularensis induces severe thymus atrophy and CD4+CD8+ thymocyte depletion

“…Deletion of thymocytes thereby eliminates the precursors of the cells that would otherwise help to maintain effective immunity against the pathogen. Besides the phenotypic changes identified in the present study, thymocytes may be also functionally affected (such as cytokine production and cell cycling) [5,12]. In this regard, although the thymus is not the site of memory cell generation and is probably not essential for the maintenance of memory cell pool, thymus destruction will nevertheless have the potential impact on the lymphocyte output and/or functional lymphocyte responses to foreign antigens.…”

“…Thus, in mice infected with type A F. tularensis by aerosol, the thymus involutes during the infectious process to the same extent as that reported after high dose i.p. infection with another type A strain of the pathogen [16] and during infections initiated by other pathogenic microbes such as L. monocytogenes [6], K. pneumoniae [7]), T. gondii [12] and Trypanosoma cruzi [18].…”

“…On the other hand, high levels of circulating cortisone were detected in acute T. cruzi infection but adrenalectomy did not prevent the development of thymus atrophy or thymocyte subset depletion [18]. Finally, thymus atrophy seen in T. gondii infection [12] or in mice treated with mycobacterial cord factor administration [15] appears to be independent of corticosteroid activity since the thymus atrophy was not prevented in infected adrenalectomized mice [12].…”

“…In this regard, experimental infection of mice with a number of bacteria (Listeria monocytogenes [6], Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Streptococcus pneumoniae [7]), viruses (murine cytomegalovirus [8], murine leukemia virus [9], HIV [10], and mouse hepatitis virus [11]), and protozoa (Toxoplasma gondii [12], and Trypanosoma cruzi) induces a severe lymphocytopaenia and marked thymus atrophy and loss of cortical lymphocytes. In addition, certain bacterial products and toxins, such as lipopolysaccharide (LPS) [13], enterotoxigenic E. coli enterotoxin [14] and mycobacterial cord factor (trehalos 6,6′-dimycolate) [15], also cause severe thymus damage.…”

Cellular changes in the spleens of mice infected with Sarcocystis muris

“…This decrease in the proportion of T cells might reflect a selective depletion of regulatory T lymphocytes caused by sarcocystis infection. A depressed T lymphocyte immunoregulatory function has also been suggested to facilitate B cell proliferation by specific or non-specific lymphocyte activators of parasite origin (14). The exact cause of the relative decrease of T cells is not known.…”