IMMUNOLOGY: Primed by Parasites

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Science  03 Feb 2006:
Vol. 311, Issue 5761, pp. 579d-581d
DOI: 10.1126/science.311.5761.579d

Collectively, parasites belonging to the genus Leishmania cause extensive mortality and morbidity around the globe. Two major forms of leishmaniasis are characterized by distinct pathologies: a life-threatening visceral disease and a cutaneous form, involving self-healing skin ulcerations. In the latter, resident macrophages and dendritic cells (DCs) of the skin take up the parasite, although in DCs this leads to the priming of Th1 cells that ultimately resolve the disease.

Woelbing et al. show that unlike macrophages, which use the complement receptor to bind and phagocytose Leishmania promastigotes, DCs acquire the parasite through Fc receptor (FcR)-mediated uptake of complexes comprising antibodies to Leishmania bound to parasitic amastigotes. Without B cells, normally resistant mice became susceptible to disease, as did animals genetically lacking the relevant FcR for IgG binding. In both cases, disease susceptibility was directly attributable to a failure of DCs to prime T cells efficiently and, consequently, to reduced production of IFN-γ. This pivotal role for antibodies to parasites in the priming of T cell immunity by DCs raises the interesting question of how the initial B cell response to the parasite itself develops. — SJS

J. Exp. Med. 10.1084/jem.20052288 (2006).

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