Chapter 5 : Murine Leishmaniasis

Major factors influencing hepatic growth of L. donovani. The graph illustrates a stylized growth curve for L. donovani infection in mice, established after intravenous inoculation of 107 amastigotes. Parasite burden is measured as Leishman Donovan units (LDU) ( 15 ). Parasites initially replicate in Kupffer cells at approximately equal rates in all strains examined. After day 3, the impact of the Gly169 → Asp169 mutation in the Slc11a1 protein becomes apparent. In Slc11a1 mutant strains (e.g., BALB/c, C57BL/6, and C57BL/10), rapid multiplication of amastigotes is also controlled by endogenous oxygen and nitrogen intermediates. Between day 14 and day 28 postinfection, the influence of MHC genes on rate of cure becomes apparent, and at this time, both CD4+and CD8+T cells cooperate to induce NO-dependent leishmanicidal activity in macrophages. The dotted line parallel to the x axis represents the limit of detection.

Defined stages in granuloma "maturation." Photomicrographs showing infected Kupffer cell (A), Kupffer cell fusion with minimal associated inflammation (B), immature granuloma (C), mature granuloma (D), and sterile, involuted granuloma (E). Lower magnification reveals that many stages of granuloma maturation are evident in the same field of view (F). Amastigotes are seen as small dots in the micrographs. For additional details, see text.

Chemokine regulation of hepatic granuloma formation. Infected Kupffer cells rapidly express chemokines (CK), but these fail to induce local recruitment of inflammatory cells in immunodeficient mice (left panels). In the presence of resident hepatic TCRγδ+or TCRαβ+T cells, chemokine production, notably of γIP-10 (CXCL10), is sustained and serves to initiate a local inflammatory focus with Kupffer cell fusion (center panel). However, TCRαβ+T cells are required to mount an organized granulomatous response (right panel).

Models for asynchronous granuloma development following L. donovani infection. In panel 1, Kupffer cells (KC) are either heterogeneous or respond in a heterogeneous manner to infection, with qualitative or quantitative differences in chemokine (CK) synthesis. In panel 2, heterogeneity results from the random distribution of resident hepatic T cells, necessary to sustain CK production. In panel 3, the stimulus for inflammation is uniform, but the availability of TCRαβ+T cells derived from the periphery is limiting.

Cytokine regulation of hepatic granuloma formation. Chemokines attract TCRαβ+T cells to infected Kupffer cells where they produce cytokines essential for generation of the full granulomatous response. Chemokines also attract monocytes and neutrophils, which may supplement the local cytokine environment. Autocrine and paracrine responses to these cytokines likely occur within the granuloma, which cannot be readily dissected with current methodology.

Enhancing granuloma formation using costimulation-based therapy. The early immature granulomatous response seen in normal mice at day 14 postinfection (A) can be substantially enhanced in both maturity and size by interfering with the negative regulatory function of CTLA-4 (B and C). Extensive epithelioid cell generation, with minimal additional mononuclear cell recruitment, is also a characteristic of sterile granulomas seen following this intervention (C). Reprinted from reference 64 with permission. Copyright 1998. The American Association of Immunologists, Inc.