Mouse models of Loa loa.

Elimination of the helminth disease, river blindness, remains challenging due to ivermectin treatment-associated adverse reactions in loiasis co-infected patients. Here, we address a deficit in preclinical research tools for filarial translational research by developing Loa loa mouse infection models. We demonstrate that adult Loa loa worms in subcutaneous tissues, circulating microfilariae (mf) and presence of filarial biomarkers in sera occur following experimental infections of lymphopenic mice deficient in interleukin (IL)-2/7 gamma-chain signaling. A microfilaraemic infection model is also achievable, utilizing immune-competent or -deficient mice infused with purified Loa mf. Ivermectin but not benzimidazole treatments induce rapid decline (>90%) in parasitaemias in microfilaraemic mice. We identify up-regulation of inflammatory markers associated with allergic type-2 immune responses and eosinophilia post-ivermectin treatment. Thus, we provide validation of murine research models to identify loiasis biomarkers, to counter-screen candidate river blindness cures and to interrogate the inflammatory etiology of loiasis ivermectin-associated adverse reactions.

Strongyloides ratti infection induces expansion of Foxp3+ regulatory T cells that interfere with immune response and parasite clearance in BALB/c mice.

To escape expulsion by their host's immune system, pathogenic nematodes exploit regulatory pathways that are intrinsic parts of the mammalian immune system, such as regulatory T cells (Tregs). Using depletion of Treg mice, we showed that Foxp3(+) Treg numbers increased rapidly during infection with the nematode Strongyloides ratti. Transient depletion of Tregs during the first days of infection led to dramatically reduced worm burden and larval output, without aggravation of immune pathology. The transient absence of Tregs during primary infection did not interfere with the generation of protective memory. Depletion of Tregs at later time points of infection (i.e., day 4) did not improve resistance, suggesting that Tregs exert their counterregulatory function during the priming of S. ratti-specific immune responses. Improved resistance upon early Treg depletion was accompanied by accelerated and prolonged mast cell activation and increased production of types 1 and 2 cytokines. In contrast, the blockade of the regulatory receptor CTLA-4 specifically increased nematode-specific type 2 cytokine production. Despite this improved immune response, resistance to the infection was only marginally improved. Taken together, we provide evidence that Treg expansion during S. ratti infection suppresses the protective immune response to this pathogenic nematode and, thus, represents a mechanism of immune evasion.

Virulence of Toxoplasma gondii is associated with distinct dendritic cell responses and reduced numbers of activated CD8+ T cells.

The Toxoplasma gondii population consists of multiple strains, defined by genotype and virulence. Previous studies have established that protective immunity to this organism is mediated by IL-12, which drives T cells to produce IFN-gamma. Paradoxically, although type I and type II strains of T. gondii both induce IL-12 and IFN-gamma in the mouse, type I parasites are lethal, whereas type II strains establish chronic infection. The cellular basis for these strain-dependent differences remains unclear. To better understand these events, the CD8(+) T cell and dendritic cell (DC) responses to transgenic, OVA-expressing type I RH (RH OVA) and type II Prugniuad (Pru OVA) parasites were examined. Pru OVA-infected mice developed a robust DC response at the site of infection and the draining lymph node and generated a population of endogenous OVA-specific CD8(+) T cells. In contrast, RH OVA-infected mice had fewer DCs and OVA-specific CD8(+) T cells. RH OVA-infected mice given preactivated OVA-specific CD8(+) T cells were protected, suggesting that reduced DC-derived signals contributed to the low OVA-specific CD8(+) T cell numbers observed during type I infection. Indeed, DC depletion prior to Pru OVA infection resulted in a failure to generate activated OVA-specific CD8(+) T cells, and IL-12p70 treatment during RH OVA infection modestly increased the number of Ag-specific cells. Together, these data are consistent with a model of immunity to T. gondii in which strain-dependent DC responses shape the generation of Ag-specific CD8(+) T cells and determine the outcome of infection.

A glycosylphosphatidylinositol-based treatment alleviates trypanosomiasis-associated immunopathology.

The GPI-anchored trypanosome variant surface glycoprotein (VSG) triggers macrophages to produce TNF, involved in trypanosomiasis-associated inflammation and the clinical manifestation of sleeping sickness. Aiming at inhibiting immunopathology during experimental Trypanosoma brucei infections, a VSG-derived GPI-based treatment approach was developed. To achieve this, mice were exposed to the GPI before an infectious trypanosome challenge. This GPI-based strategy resulted in a significant prolonged survival and a substantial protection against infection-associated weight loss, liver damage, acidosis, and anemia; the latter was shown to be Ab-independent and correlated with reduced macrophage-mediated RBC clearance. In addition, GPI-based treatment resulted in reduced circulating serum levels of the inflammatory cytokines TNF and IL-6, abrogation of infection-induced LPS hypersensitivity, and an increase in circulating IL-10. At the level of trypanosomiasis-associated macrophage activation, the GPI-based treatment resulted in an impaired secretion of TNF by VSG and LPS pulsed macrophages, a reduced expression of the inflammatory cytokine genes TNF, IL-6, and IL-12, and an increased expression of the anti-inflammatory cytokine gene IL-10. In addition, this change in cytokine pattern upon GPI-based treatment was associated with the expression of alternatively activated macrophage markers. Finally, the GPI-based treatment also reduced the infection-associated pathology in Trypanosoma congolense and Trypanosoma evansi model systems as well as in tsetse fly challenge experiments, indicating potential field applicability for this intervention strategy.

Characterization of peripheral blood lymphocyte subsets in patients with acute Plasmodium falciparum and P. vivax malaria infections at Wonji Sugar Estate, Ethiopia.

We investigated the absolute counts of CD4+, CD8+, B, NK, and CD3+ cells and total lymphocytes in patients with acute Plasmodium falciparum and Plasmodium vivax malaria. Three-color flow cytometry was used for enumerating the immune cells. After slide smears were stained with 3% Giemsa stain, parasite species were detected using light microscopy. Data were analyzed using STATA and SPSS software. A total of 204 adults of both sexes (age, >15 years) were included in the study. One hundred fifty-eight were acute malaria patients, of whom 79 (50%) were infected with P. falciparum, 76 (48.1%) were infected with P. vivax, and 3 (1.9%) were infected with both malaria parasites. The remaining 46 subjects were healthy controls. The leukocyte count in P. falciparum patients was lower than that in controls (P=0.015). Absolute counts of CD4+, CD8+, B, and CD3+ cells and total lymphocytes were decreased very significantly during both P. falciparum (P<0.0001) and P. vivax (P<0.0001) infections. However, the NK cell count was an exception in that it was not affected by either P. falciparum or P. vivax malaria. No difference was found in the percentages of CD4, CD8, and CD3 cells in P. falciparum or P. vivax patients compared to controls. In summary, acute malaria infection causes a depletion of lymphocyte populations in the peripheral blood. Thus, special steps should be taken in dealing with malaria patients, including enumeration of peripheral lymphocyte cells for diagnostic purposes and research on peripheral blood to evaluate the immune status of patients.

Memory Th2 effector cells can develop in the absence of B7-1/B7-2, CD28 interactions, and effector Th cells after priming with an intestinal nematode parasite.

B7-1/B7-2 interactions are required for many Th2-cell mediated primary immune responses including the response that follows infection with the intestinal nematode parasite, Heligmosomoides polygyrus. However, few studies have examined the role of B7-1/B7-2/CD28 interactions in the development of a Th2 memory immune response. We examined the development of the memory Th2 response to H. polygyrus in BALB/c mice deficient in both B7-1 and B7-2 (B7-1/B7-2(-/-)) and in BALB/c mice deficient in CD28 (CD28(-/-)). Following primary inoculation with H. polygyrus, adult worms in the gut were cleared with an anti-helminthic drug and mice were subsequently challenge-inoculated with H. polygyrus larvae. The memory Th2 response is readily distinguished by its inhibitory effect on adult worm maturation, resulting in marked reductions in adult worm egg production that are not observed during the primary immune response. Following H. polygyrus challenge inoculation, comparable decreases in egg production and similar increases in mesenteric lymph node cell IL-4 production were observed in B7-1/B7-2(-/-) and B7-1/B7-2(+/+) mice. However, elevations in total serum IgG1 and IgE were reduced, while increases in serum Ag-specific IgG1 and IgE and germinal center formation were blocked in H. polygyrus-challenged B7-1/B7-2(-/-) mice. In contrast, in H. polygyrus-challenged CD28(-/-) mice, marked elevations in Ag-specific IgG1 and IgE and increased germinal center formation were observed. The results of these studies demonstrate that effector Th2 memory cells that produce IL-4 and mediate host defense can develop when B7-1/B7-2 interactions, and associated effector Th2 cell development, are blocked during priming. However, humoral immunity is impaired and differentially affected in B7-1/B7-2(-/-) mice and CD28(-/-) mice following H. polygyrus challenge.

Cutting edge: IL-4 receptor expression by non-bone marrow-derived cells is required to expel gastrointestinal nematode parasites.

Expulsion of two gastrointestinal nematode parasites, Nippostrongylus brasiliensis and Trichinella spiralis, is similar in that both require IL-4Ralpha expression, but different in that T cells and mast cells are required for IL-4-induced expulsion of T. spiralis but not N. brasiliensis. To examine the role of IL-4Ralpha signaling in immunity to these parasites, we studied worm expulsion in chimeric mice that selectively expressed IL-4Ralpha on bone marrow-derived or non-bone marrow-derived cells. N. brasiliensis was expelled by mice that expressed IL-4Ralpha only on non-bone marrow-derived cells, but not by mice that expressed IL-4Ralpha only on bone marrow-derived cells. Although T. spiralis expulsion required IL-4Ralpha expression by both bone marrow- and non-bone marrow-derived cells, IL-4 stimulation eliminated the requirement for IL-4Ralpha expression by bone marrow-derived cells. Thus, direct IL-4Ralpha signaling of nonimmune gastrointestinal cells may be generally required to induce worm expulsion, even when mast cell and T cell responses are also required.

Gamma delta T cell-deficient mice have a down-regulated CD8+ T cell immune response against Encephalitozoon cuniculi infection.

Gamma(delta) T cells have been reported to play an essential effector role during the early immune response against a wide variety of infectious agents. Recent studies have suggested that the gamma(delta) T cell subtype may also be important for the induction of adaptive immune response against certain microbial pathogens. In the present study, an early increase of gamma(delta) T cells during murine infection with Encephalitozoon cuniculi, an intracellular parasite, was observed. The role of gamma(delta) T cells against E. cuniculi infection was further evaluated by using gene-knockout mice. Mice lacking gamma(delta) T cells were susceptible to E. cuniculi infection at high challenge doses. The reduced resistance of delta(-/-) mice was attributed to a down-regulated CD8+ immune response. Compared with parental wild-type animals, suboptimal Ag-specific CD8+ T cell immunity against E. cuniculi infection was noted in delta(-/-) mice. The splenocytes from infected knockout mice exhibited a lower frequency of Ag-specific CD8+ T cells. Moreover, adoptive transfer of immune TCR(alpha)beta+ CD8+ cells from the delta(-/-) mice failed to protect naive CD8(-/-) mice against a lethal E. cuniculi challenge. Our studies suggest that gamma(delta) T cells, due to their ability to produce cytokines, are important for the optimal priming of CD8+ T cell immunity against E. cuniculi infection. This is the first evidence of a parasitic infection in which down-regulation of CD8+ T cell immune response in the absence of gamma(delta) T cells has been demonstrated.