Summary Exposure to a plethora of environmental challenges commonly triggers pathological type 2 cell-mediated inflammation. Here we report the pathological role of the Wnt antagonist Dickkopf-1 (Dkk-1) upon allergen challenge or non-healing parasitic infection. The increased circulating amounts of Dkk-1 polarized T cells to T helper 2 (Th2) cells, stimulating a marked simultaneous induction of the transcription factors c-Maf and Gata-3, mediated by the kinases p38 MAPK and SGK-1, resulting in Th2 cell cytokine production. Circulating Dkk-1 was primarily from platelets, and the increase of Dkk-1 resulted in formation of leukocyte-platelet aggregates (LPA) that facilitated leukocytes infiltration to the affected tissue. Functional inhibition of Dkk-1 impaired Th2 cell cytokine production and leukocyte infiltration, protecting mice from house dust mite (HDM)-induced asthma or Leishmania major infection. These results highlight that Dkk-1 from thrombocytes is an important regulator of leukocyte infiltration and polarization of immune responses in pathological type 2 cell-mediated inflammation.

Engagement of the T cell antigen receptor (TCR) during antigen presentation initiates a coordinated action of a large number of signaling proteins and ion channels. AHNAK1 is a scaffold protein, highly expressed by CD4+ T cells, and is a critical component for calcium signaling. We showed that AHNAK1-deficient mice were highly susceptible to Leishmania major infection. AHNAK1-deficient CD4+ T cells responded poorly to TCR stimulation in vitro with low proliferation and low Interleukin-2 production. Furthermore, AHNAK1 deficiency resulted in a reduced calcium influx upon TCR crosslinking and subsequent poor activation of the transcription factor NFAT. AHNAK1 was required for plasma membrane expression of L-type calcium channels alpha 1S (Cav1.1), probably through its interaction with the beta regulatory subunit. Thus, AHNAK1 plays an essential role in T cell Ca2+ signaling through Cav1 channels, triggered via TCR activation; therefore, AHNAK1 is a potential target for therapeutic intervention.

The levels of protection found in vaccine studies of murine visceral leishmaniasis are significantly lower than for cutaneous leishmaniasis; whether this is due to the high-challenge murine model employed and/or is a consequence of differences required in tissue-specific local immune responses is not understood. Consequently, an intradermal murine model of visceral leishmaniasis has been explored. Intradermal inoculation established a chronic infection in susceptible mice which was associated with a pattern of parasite clearance with time postinfection in the liver and skin; in contrast, parasite persistence and expansion was observed in lymphoid tissue (spleen and draining lymph node). The course of disease found appears to be similar to those reported for subclinical canine and human visceral leishmaniasis. Clearance of parasites from the skin was correlated with an inflammatory response and the infiltration and activation of CD4 ؉ and CD8 ؉ T cells. In contrast, in lymphoid tissue (lymph node or spleen), the production of Th1/Th2 cytokines (interleukin-4 [IL-4], IL-10, and gamma interferon) appeared to correlate with parasite burden and pathogenesis. In vaccination experiments employing the Leishmania infantum D-13 (p80) antigen, significantly higher levels of protection were found with the intradermal murine model (29 to 7,500-fold more than naive controls) than were found with a low-dose intravenous infection model (9 to 173-fold). Thus, this model should prove useful for further investigation of disease pathogenesis as well as vaccine studies of visceral leishmaniasis.

Leishmania (Viannia) organisms are the most prevalent etiologic agents of human cutaneous leishmaniasis in the Americas. Nevertheless, our knowledge of the immunological mechanisms exploited by L. (Viannia) organisms remains limited and the mechanisms underlying disease are not well understood. Here, we report the development of a BALB/c mouse model of L. (V.) panamensis infection that is able to reproduce chronic disease, with persistent infection and clinically evident lesions for over 1 year. The immune response of the mouse resembles that found for L. (V.) panamensis-infected patients with chronic and recurrent lesions, presenting a mixed Th1/Th2 response with the presence of TNF-α, IFN-γ, IL-10 and IL-13. Using immunodeficient mice, the critical role for IL-13 and/or IL-4Rα in determining susceptibility to chronic infection was evident. With the induction of healing in the immunodeficient mice, increases in IFN-γ and IL-17 were found, concomitant with parasite control and elimination. Specifically, increases in CD4+ (but not CD8+) T cells producing IFN-γ were observed. These results suggest that IL-13 represents an important target for disease control of L. (V.) panamensis infection. This murine model should be useful to further understand the pathology associated with chronic disease and to develop methods for the treatment and prevention of leishmaniasis caused by L. (Viannia) parasites.

In visceral leishmaniasis, the draining LN (DLN) is the initial site for colonization and establishment of infection after intradermal transmission by the sand fly vector; however, little is known about the developing immune response within this site. Using an intradermal infection model, which allows for parasite visceralization, we have examined the ongoing immune responses in the DLN of BALB/c mice infected with Leishmania infantum. Although not unexpected, at early times post-infection there is a marked B-cell expansion in the DLN, which persists throughout infection. However, the characteristics of this response were of interest; as early as day 7 post-infection, polyclonal antibodies (TNP, OVA, chromatin) were observed and the levels appeared comparable to the specific anti-leishmania response. Although B-cell-deficient J h D BALB/c mice are relatively resistant to infection, neither B-cell-derived IL-10 nor B-cell antigen presentation appear to be primarily responsible for the elevated parasitemia. However, passive transfer and reconstitution of J h D BALB/c with secretory immunoglobulins, (IgM or IgG; specific or non-specific immune complexes) results in increased susceptibility to L. infantum infection. Further, J h D BALB/c mice transgenetically reconstituted to secrete IgM demonstrated exacerbated disease in comparison to WT BALB/c mice as early as 2 days post-infection. Evidence suggests that complement activation (generation of C5a) and signaling via the C5a receptor (CD88) is related to the disease exacerbation caused by IgM rather than cytokine levels (IL-10 or IFN-c). Overall these studies indicate that polyclonal B-cell activation, which is known to be associated with human visceral leishmaniasis, is an early and intrinsic characteristic of disease and may represent a target for therapeutic intervention.Key words: Antibody . C5a . Parasitic protozoan IntroductionVisceral leishmaniasis (VL) is a potentially fatal human disease caused by the intracellular protozoan parasites Leishmania donovani and L. infantum/L. chagasi. The immune response to VL is complex and has been shown to be organ-specific, differing significantly dependent upon the site of infection examined (liver versus spleen) [1,2]. Although the lymph node is thought to be analogous to the spleen, there are considerable developmental as well as structural and functional differences [3,4]. Reflective of this is the fact that although both spleens and lymph nodes from fatal human cases of VL exhibit destruction of normal architecture, follicular DC (FDC) and GC are lost in spleens, while continuing to be present in lymph nodes [5]. However, few Eur. J. Immunol. 2010. 40: 1355-1368 DOI 10.1002 Immunity to infection 1355 experimental studies to date have examined the lymph node responses that occur as a result of infection and have instead focused on the spleen where, akin to observations in humans, the destruction of FDC and GC is evident [6]. Although these observations in the spleen might appear to preclude a role for B cells in disea...