Neutralization of IL-12 demonstrates the existence of discrete organ-specific phases in the control ofLeishmania donovani

Abstract

IL-12 plays a key role in stimulating both innate and antigen-specific immune responses against a number of intracellular pathogens. A neutralizing anti-IL-12 monoclonal antibody (mAb) was used to define and compare the role of endogenous IL-12 in the liver and spleen of mice infected with Leishmania donovani. IL-12 neutralization both early and late in infection caused delayed resolution of parasite load, a transient decrease in IFN-gamma, IL-4, TNF-alpha and inducible nitric oxide synthase (NOS-2) production, and suppressed tissue granuloma formation in the liver of genetically susceptible BALB/c mice. In contrast to the liver of BALB/c mice, neutralization of IL-12 had no effect on parasite burden in the spleen over the first 28 days of infection. However, IL-12 appeared to be critical for the development of mechanisms which subsequently contain the growth of persistent parasites in this organ in that neutralization of IL-12 dramatically enhanced parasite growth after day 28 of infection. Following IL-12 neutralization, the later unchecked growth of parasites in the spleen was coincident with an extensive breakdown of the tissue microarchitecture. Immunohistochemical studies revealed that IL-12 was largely produced by uninfected cells in L. donovani-infected BALB/c mice. In contrast, the course of infection in the liver and spleen of genetically resistant CBA/n mice was unaffected by the administration of anti-IL-12 mAb. These results suggest that the liver and spleen in susceptible BALB/c mice have different temporal requirements for IL-12 in controlling L. donovani infection, whereas IL-12 plays little role in either organ in resistant CBA/n mice. In addition, IL-12 appears to be involved in the generation of both Th1 and Th2 responses during L. donovani infection in BALB/c mice.

Evaluation of TNF-α, IL-4, and IL-10 and parasite density in spleen and liver ofL. (L.) chagasinaturally infected dogs

“…This can be explained by the ability of the spleen to express high levels of this cytokine, as TNF-a mediation is required for spleen tissue remolding when the parasite persists in this organ, as seen in mice infected with L. (L.) donovani (Engwerda et al, 1998). These results are similar to those reported by Lage et al (2007) in which no difference in the level of TNF-a in spleen cells was observed between symptomatic and asymptomatic dogs naturally infected with L. (L.) chagasi.…”

Immunization with a Recombinant Stage-Regulated Surface Protein fromLeishmania donovaniInduces Protection Against Visceral Leishmaniasis

“…First, the finding that rHASPB1 is highly immunogenic and protective, even in the absence of adjuvant, suggested that this molecule may have inherent adjuvant activity, possibly mediated through the induction of IL-12 (36). IL-12 is a key component in the early response to L. donovani, and neutralization of IL-12 over the first few days postinfection leads to elevated parasite burdens in both the spleen and liver (34). Recent studies suggest three main routes leading to IL-12 production by DC.…”

“…Data represent the frequency of IL-12p40-positive DC per 100 white pulp profiles (visualized by the injection of India ink 1 h before infection (33)). To detect IL-12p70, we used an enzyme-linked immunospot (ELISPOT) assay, as described elsewhere (34). Briefly, spleen cells (10 5 /well in complete RPMI with 10% FCS) were seeded into 96-well plates precoated with mAb 9A5 (anti-IL12p75; 5 g/ml overnight at 4°C).…”

Endogenous IL-12 synthesis is not required to prevent hyperexpression of type 2 cytokine and antibody responses

“…Anguita et al [30] found that administration of anti-IL-12 Ab to C3H mice over the course of lyme borreliosis infection greatly reduced type 1 activation but failed to enhance either IL-4 or serum IgE. Similarly, Engwerda et al [46] observed no increase in IL-4 following anti-IL-12 treatment of Leishmania donovani-infected BALB/c mice. While one might argue that these represent exceptions, reflecting incomplete neutralization of endogenous IL-12 synthesis in vivo, two recent studies examining the impact of mycobacterial infection in IL-12 -/-models found that IL-4 responses were not enhanced in the absence of endogenous IL-12 production [32,35].…”