Multi-factorial immune mechanisms underlie protection induced with radiationattenuated Plasmodia sporozoites (c-spz). Spz pass through Kupffer cells (KC) before invading hepatocytes but the involvement of KC in protection is poorly understood. In this study we investigated whether c-spz-immune KC respond to infectious spz in a manner that is distinct from the response of naive KC to infectious spz. KC were isolated from (1) naive, (2) spz-infected, (3) c-spz-immune, and (4) c-spz-immune-challenged C57BL/6 mice and examined for the expression of MHC class I and II, CD40 and CD80/CD86, IL-10 and IL-12 responses and antigen-presenting cell (APC) function. KC from c-spz-immune-challenged mice up-regulated class I and costimulatory molecules and produced elevated IL-12p40, relative to naive KC. In contrast, KC from naive mice exposed to infectious spz down-modulated class I and IL-12p40 was undetectable. Accordingly, KC from spz-infected mice had reduced APC function, while KC from c-spz-immune-challenged mice exhibited augmented APC activity. The nearly opposite responses are consistent with the fact that spz challenge of c-spz-immune mice results in long-lasting sterile protection, while infection of naive mice always results in malaria.

Murine hydatid cysts of Echinococcus granulosus were incubated in vitro in the presence of nitric oxide produced from S-nitroso-N-acetylpenicillamine (SNAP) or interferon-gamma activated peritoneal macrophages. In both situations, evidence of cyst damage and death was observed by microscopy in over 77% of cysts after 3 days, indicating that intact hydatid cysts could be susceptible to a Th1 driven macrophage attack. A crude extract of the laminated layer from cysts was found to be able to reduce the production of nitric oxide from activated macrophages in vitro and in vivo and this may have been due to phagocytosis of laminated layer fragments by the macrophages. The results indicate that, although cysts may be susceptible to the effects of nitric oxide, the laminated layer may be involved in downregulating nitric oxide production.

Ag-specific memory T cell responses elicited by infections or vaccinations are inextricably linked to long-lasting protective immunity. Studies of protective immunity amongst residents of malaria endemic areas indicate that memory responses to Plasmodia antigens are not adequately developed or maintained, as persons who survive episodes of childhood malaria are still vulnerable to either persistent or intermittent malaria infections. In contrast, multiple exposures to radiation-attenuated Plasmodia sporozoites (γ-spz) induce long-lasting protective immunity to experimental sporozoite challenge. We previously demonstrated that sterile protection induced by Plasmodium berghei (Pb) γ-spz is MHC-class I-dependent and CD8 T cells are the key effectors. IFN-γ+CD8 T cells that arise in Pb γ-spz immunized B6 mice are found predominantly in the liver and are sensitive to levels of liver-stage Ag depot and they express CD44hiCD62Llo markers indicative of effector/effector memory (E/EM) phenotype. The developmentally related central memory (CM) CD8 T cells express elevated levels of CD122 (IL-15Rβ), which suggests that CD8 TCM cells depend upon IL-15 for maintenance. Using IL-15 deficient mice, we demonstrate here that although protective immunity is inducible in these mice, protection is short-lived, mainly owing to the inability of CD8 TCM cells to survive in the IL-15 deficient milieu. We present a hypothesis consistent with a model whereby intrahepatic CD8 TCM cells, being maintained by IL-15-mediated survival and basal proliferation, are conscripted into CD8 TE/EM cell pool during subsequent infections.

MHC class I dependent CD8 + T cells are essential for protection induced by radiationattenuated Plasmodium sporozoites (RAS) in murine malaria models. Apart from the mechanism of activation of CD8 + T cells specific for the circumsporozoite protein, the major sporozoite antigen (Ag), CD8 + T cells specific for other exoerythrocytic Ags that have been shown to mediate protection have not been thoroughly investigated. Specifically, mechanisms of processing and presentation of exoerythrocytic Ags, which includes liver stage (LS) Ags, remain poorly understood. We hypothesize that as exogenous proteins, LS Ags are processed by mechanisms involving either the TAP-dependent phagosomalto-cytosol or TAP-independent vacuolar pathway of cross-presentation. We used TAPdeficient mice to investigate whether LS Ag mediated induction of naïve CD8 + T cells and their recall during sporozoite challenge occur by the TAP-dependent or TAP-independent pathways. On the basis of functional attributes, CD8 + T cells were activated via the TAPindependent pathway during immunizations with Plasmodium berghei RAS; however, IFN-γ + CD8 + T cells previously induced by P. berghei RAS in TAP-deficient mice failed to be recalled against sporozoite challenge and the mice became parasitemic. On the basis of these observations, we propose that TAP-associated Ag processing is indispensable for sterile protection induced with P. berghei RAS.Keywords: Antigen presenting cells · CD8 + T cells · Liver · Plasmodium · Transporter associated with antigen processing (TAP) Additional supporting information may be found in the online version of this article at the publisher's web-site Introduction CD8 + T cells provide a critical network of responses that underlie lasting protective immunity against viral, microbial, and parasitic infections [1]. A subset of antigen (Ag) induced CD8 + T cells acquire an effector (E) function and these CD8 + effector T (T E ) cells become poised to eliminate pathogen infected cells, Correspondence: Dr. Urszula Krzych e-mail: Urszula.Krzych1.civ@mail.mil a process that is typically MHC I dependent. The induction of Ag-specific CD8 + T cells requires ligation of the TCR by MHC I:peptide complexes that are formed during Ag processing and displayed on APCs, followed by the provision of secondary and tertiary signals, such as costimulatory molecules and cytokines, respectively [2,3]. Several distinct mechanisms of Ag processing have been described for the MHC I pathway and the utilization of a particular pathway depends in part on the Ag itself. For example, most endogenous Ags, such as viral proteins synthesized within the cytosol of infected host cells, are processed along the classical pathway involving proteosomal degradation followed by Published 2015. This article is a U.S. Government work and is in the public domain in the USA www.eji-journal.eu 886Alexander Pichugin et al. Eur. J. Immunol. 2016. 46: 885-896 TAP-dependent transfer of oligopeptides into the ER. Subsequent trimming by ER aminopeptidase associated with A...

Induction of long-lasting protective immunity to malaria by repetitive immunization with P. berghei γ radiation-attenuated sporozoites (γ-spz) requires MHC class I-restricted CD8+ T cells, implying that γ-spz/liver stage derived antigens have to be presented through one of the cross-presentation pathways. Based on accumulation of proliferating and IFN-γ producing effector/memory CD8+ T cells in the livers of TAP−/− mice, we showed that TAP-independent vacuolar pathway efficiently operates in vivo during priming and subsequent boosts with γ-spz. Likewise, infectious sporozoite challenge increased the number of IFN-γ+ CD8+ T cells in γ-spz immune TAP−/− mice and induced IFN-γ production by wt γ-spz immune CD8+ T cells transferred into TAP−/− environment suggesting that γ-spz/liver stage derived MHC class I specific peptides generated in a TAP-independent manner participate in response to infectious sporozoites. Nevertheless, the pattern of IFN-γ secretion, parasitemia and survival data upon infectious sporozoite challenge clearly indicated that TAP-associated antigen processing is indispensable for sterile protection.