Tracey L. Mynott

Locally Up-regulated Lymphotoxin α, Not Systemic Tumor Necrosis Factor α, Is the Principle Mediator of Murine Cerebral Malaria

Cerebral malaria (CM) causes death in children and nonimmune adults. TNF-α has been thought to play a key role in the development of CM. In contrast, the role of the related cyto-kine lymphotoxin α (LTα) in CM has been overlooked. Here we show that LTα, not TNFα, is the principal mediator of murine CM. Mice deficient in TNFα (B6.TNFα−/−) were as susceptible to CM caused by Plasmodium berghei (ANKA) as C57BL/6 mice, and died 6 to 8 d after infection after developing neurological signs of CM, associated with perivascular brain hemorrhage. Significantly, the development of CM in B6.TNFα−/− mice was not associated with increased intracellular adhesion molecule (ICAM)-1 expression on cerebral vasculature and the intraluminal accumulation of complement receptor 3 (CR3)-positive leukocytes was moderate. In contrast, mice deficient in LTα (B6.LTα−/−) were completely resistant to CM and died 11 to 14 d after infection with severe anemia and hyperparasitemia. No difference in blood parasite burden was found between C57BL/6, B6.TNFα−/−, and B6.LTα−/− mice at the onset of CM symptoms in the two susceptible strains. In addition, studies in bone marrow (BM) chimeric mice showed the persistence of cerebral LTα mRNA after irradiation and engraftment of LTα-deficient BM, indicating that LTα originated from a radiation-resistant cell population.

A Role for Tumor Necrosis Factor-α in Remodeling the Splenic Marginal Zone during Leishmania donovani Infection

The development of secondary lymphoid organs is a highly regulated process, mediated by tumor necrosis factor (TNF) family cytokines. In contrast, the mechanisms controlling changes in lymphoid architecture that occur during infectious disease are poorly understood. Here we demonstrate that during infection with Leishmania donovani, the marginal zone of mice undergoes extensive remodeling, similar in extent to developmental abnormalities in mice lacking some TNF family cytokines. This process is selective, comprising a dramatic and rapid loss of marginal zone macrophages (MZMs). As a functional consequence, lymphocyte traffic into the white pulp is impaired during chronic leishmaniasis. Significantly, MZMs were preserved in L. donovani-infected B6.TNF-alpha(-/-) mice or mice that received anti-TNF-alpha antibodies, whereas studies in CD8(+) T-cell-deficient mice and in mice lacking functional CD95L, excluded a direct role for either cytotoxic T lymphocyte activity or CD95-mediated apoptosis in this process. Loss of MZMs was independent of parasite burden, yet could be partially prevented by chemotherapy, which in turn reduced endogenous TNF-alpha levels. This is the first report of an infectious agent causing selective and long-lasting changes to the marginal zone via TNF-alpha-mediated mechanisms, and illustrates that those cytokines involved in establishing lymphoid architecture during development, may also play a role in infection-induced lymphoid tissue remodeling.