B-cell memory in malaria: Myths and realities

B-cell and antibody responses to Plasmodium spp., the parasite that causes malaria, are critical for control of parasitemia and associated immunopathology. Antibodies also provide protection to reinfection. Long-lasting B-cell memory has been shown to occur in response to Plasmodium spp. in experimental model infections, and in human malaria. However, there are reports that antibody responses to several malaria antigens in young children living with malaria are not similarly long-lived, suggesting a dysfunction in the maintenance of circulating antibodies. Some studies attribute this to the expansion of atypical memory B cells (AMB), which express multiple inhibitory receptors and activation markers, and are hyporesponsive to B-cell receptor (BCR) restimulation in vitro. AMB are also expanded in other chronic infections such as tuberculosis, hepatitis B and C, and HIV, as well as in autoimmunity and old age, highlighting the importance of understanding their role in immunity. Whether AMB are dysfunctional remains controversial, as there are also studies in other infections showing that AMB can produce isotype-switched antibodies and in mouse can contribute to protection against infection. In light of these controversies, we review the most recent literature on either side of the debate and challenge some of the currently held views regarding B-cell responses to Plasmodium infections.     

The enigma of memory B cells in malaria

Malaria is a major public health problem particularly in the tropics. It is caused by protozoan parasites belonging to the genus Plasmodium and is transmitted by Anopheles mosquitoes. Currently, strategies to control malaria include vector control measures, chemoprophylaxis, and efficient diagnosis and treatment. The availability of a highly efficacious malaria vaccine would greatly facilitate malaria control and possibly eradicate malaria. Efforts to design such malaria vaccines are underway but are greatly hampered by the poor understanding of how immune memory to malaria is generated and maintained. In this issue of the European Journal of Immunology, Wykes and colleagues [Eur. J. Immunol. 2012. 42: 3291–3301] demonstrate that experimental malaria infection lowers the expression of B‐cell‐activating factor in DCs, thereby compromising the ability of these DCs to stimulate memory B cells and sustain the survival of Ab‐secreting cells. These findings provide potential clues in the quest for better understanding of immunity to malaria as discussed in this Commentary.     

The interaction between DC and Plasmodium berghei/chabaudi‐infected erythrocytes in mice involves direct cell‐to‐cell contact,internalization and TLR

Early interactions between blood‐stage Plasmodium parasites and cells of the innate immune system are very important in shaping the adaptive immune response to malaria, and a number of studies have suggested that DC are responsible for this phenomenon. Therefore, we examined the capacity of murine BM‐derived DC to internalize parasites, be activated and produce cytokines upon in vitro interaction with murine erythrocytes infected with two different strains of rodent malaria parasites (Plasmodium berghei and Plasmodium chabaudi chabaudi). We show that the increased expression of MHC class II and co‐stimulatory molecules and increased production of cytokines by DC following Plasmodium infection involves internalization of infected RBC. Such DC activation not only requires direct cell‐to‐cell contact and internalization of infected RBC by DC but also involves TLR4, TLR9, MyD88 and signaling via NF‐κB; however, TLR involvement in survival to Plasmodium infection was found to be negligible.     

Dendritic cells, pro-inflammatory responses, and antigen presentation in a rodent malaria infection

Summary: An infection of mice with Plasmodium chabaudi is characterized by a rapid and marked inflammatory response with a rapid but regulated production of interleukin‐12 (IL‐12), tumor necrosis factor‐α (TNF‐α), and interferon‐γ (IFN‐γ). Recent studies have shown that dendritic cells (DCs) are activated in vivo in the spleen, are able to process and present malaria antigens during infection, and may provide a source of cytokines that contribute to polarization of the CD4 T‐cell response. P. chabaudi‐infected erythrocytes are phagocytosed by DCs, and peptides of malaria proteins are presented on major histocompatibility complex (MHC) class II. The complex disulfide‐bonded structure of some malaria proteins can impede their processing in DCs, which may affect the magnitude of the CD4 T‐cell response and influence T‐helper 1 (Th1) or Th2 polarization. DCs exhibit a wide range of responses to parasite‐infected erythrocytes depending on their source, their maturational state, and the Plasmodium species or strain. P. chabaudi‐infected erythrocytes stimulate an increase in the expression of costimulatory molecules and MHC class II on mouse bone marrow‐derived DCs, and they are able to induce the production of pro‐inflammatory cytokines such as IL‐12, TNF‐α, and IL‐6, thus enhancing the Th1 response of naïve T cells. IFN‐γ and TNF‐α play a role in both protective immunity and the pathology of the infection, and the inflammatory disease may be regulated by IL‐10 and transforming growth factor‐β. It will therefore be important to elucidate the host and parasite molecules that are involved in activation or suppression of the DCs and to understand the interplay between these opposing forces on the host response in vivo during a malaria infection.     

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Abstract

Malaria, an infectious disease caused by a protozoal parasite (Plasmodium spp.), currently kills more than 1 million people annually. The infection causes disease in young children and pregnant women in Africa and in many developing countries. In humans, malaria infection induces neurologic impairment, anemia, hypoglycemia, and low birth weight and interferes with normal development and survival. Experimental animal models have been extensively used in malaria research for pathogenesis studies and in drug and vaccine development. We describe here the histologic findings in the bone marrows of rhesus macaques (Macaca Mulatta) experimentally infected with simian malaria (Plasmodium knowlesi). In addition, we compare two histological techniques and discuss decalcification solutions and other pertinent procedures of critical importance in the evaluation of these bone marrow specimens. (The J Histotechnol 32(4):172–174, 2009)     

Dendritic cells treated with crude Plasmodium berghei extracts acquire immune‐modulatory properties and suppress the development of autoimmune neuroinflammation

Dendritic cells (DCs) are professional antigen‐presenting cells specifically targeted during Plasmodium infection. Upon infection, DCs show impaired antigen presentation and T‐cell activation abilities. In this study, we aimed to evaluate whether cellular extracts obtained from Plasmodium berghei‐infected erythrocytes (PbX) modulate DCs phenotypically and functionally and the potential therapeutic usage of PbX‐modulated DCs in the control of experimental autoimmune encephalomyelitis (EAE, the mouse model for human multiple sclerosis). We found that PbX‐treated DCs have impaired maturation and stimulated the generation of regulatory T cells when cultured with naive T lymphocytes in vitro. When adoptively transferred to C57BL/6 mice the EAE severity was reduced. Disease amelioration correlated with a diminished infiltration of cytokine‐producing T cells in the central nervous system as well as the suppression of encephalitogenic T cells. Our study shows that extracts obtained from P. berghei‐infected erythrocytes modulate DCs towards an immunosuppressive phenotype. In addition, the adoptive transfer of PbX‐modulated DCs was able to ameliorate EAE development through the suppression of specific cellular immune responses towards neuro‐antigens. To our knowledge, this is the first study to present evidence that DCs treated with P. berghei extracts are able to control autoimmune neuroinflammation.     

Preferentially expanding Vγ1+ γδ T cells are associated with protective immunity against Plasmodium infection in mice

γδ T cells play a crucial role in controlling malaria parasites. Dendritic cell (DC) activation via CD40 ligand (CD40L)‐CD40 signaling by γδ T cells induces protective immunity against the blood‐stage Plasmodium berghei XAT (PbXAT) parasites in mice. However, it is unknown which γδ T‐cell subset has an effector role and is required to control the Plasmodium infection. Here, using antibodies to deplete TCR Vγ1⁺ cells, we saw that Vγ1⁺ γδ T cells were important for the control of PbXAT infection. Splenic Vγ1⁺ γδ T cells preferentially expand and express CD40L, and both Vγ1⁺ and Vγ4⁺ γδ T cells produce IFN‐γ during infection. Although expression of CD40L on Vγ1⁺ γδ T cells is maintained during infection, the IFN‐γ positivity of Vγ1⁺ γδ T cells is reduced in late‐phase infection due to γδ T‐cell dysfunction. In Plasmodium‐infected IFN‐γ signaling‐deficient mice, DC activation is reduced, resulting in the suppression of γδ T‐cell dysfunction and the dampening of γδ T‐cell expansion in the late phase of infection. Our data suggest that Vγ1⁺ γδ T cells represent a major subset responding to PbXAT infection and that the Vγ1⁺ γδ T‐cell response is dependent on IFN‐γ‐activated DCs.     

A central role for free heme in the pathogenesis of severe malaria: the missing link?

Malaria, the disease caused by Plasmodium infection, is endemic to poverty in so-called underdeveloped countries. Plasmodium falciparum, the main infectious Plasmodium species in sub-Saharan countries, can trigger the development of severe malaria, including cerebral malaria, a neurological syndrome that claims the lives of more than one million children (<5 years old) per year. Attempts to eradicate Plasmodium infection, and in particular its lethal outcomes, have so far been unsuccessful. Using well-established rodent models of malaria infection, we found that survival of a Plasmodium-infected host is strictly dependent on the host’s ability to up-regulate the expression of heme oxygenase-1 (HO-1 encoded by the gene Hmox1). HO-1 is a stress-responsive enzyme that catabolizes free heme into biliverdin, via a reaction that releases Fe and generates the gas carbon monoxide (CO). Generation of CO through heme catabolism by HO-1 prevents the onset of cerebral malaria. The protective effect of CO is mediated via its binding to cell-free hemoglobin (Hb) released from infected red blood cells during the blood stage of Plasmodium infection. Binding of CO to cell-free Hb prevents heme release and thus generation of free heme, which we found to play a central role in the pathogenesis of cerebral malaria. We will address hereby how defense mechanisms that prevent the deleterious effects of free heme, including the expression of HO-1, impact on the pathologic outcome of Plasmodium infection and how these may be used therapeutically to suppress its lethal outcomes.     

Malaria parasites (Plasmodium spp.) infecting introduced, native and endemic New Zealand birds

Avian malaria is caused by intracellular mosquito-transmitted protist parasites in the order Haemosporida, genus Plasmodium. Although Plasmodium species have been diagnosed as causing death in several threatened species in New Zealand, little is known about their ecology and epidemiology. In this study, we examined the presence, microscopic characterization and sequence homology of Plasmodium spp. isolates collected from a small number of New Zealand introduced, native and endemic bird species. We identified 14 Plasmodium spp. isolates from 90 blood or tissue samples. The host range included four species of passerines (two endemic, one native, one introduced), one species of endemic pigeon and two species of endemic kiwi. The isolates were associated into at least four distinct clusters including Plasmodium (Huffia) elongatum, a subgroup of Plasmodium elongatum, Plasmodium relictum and Plasmodium (Noyvella) spp. The infected birds presented a low level of peripheral parasitemia consistent with chronic infection (11/15 blood smears examined). In addition, we report death due to overwhelming parasitemia in a blackbird, a great spotted kiwi and a hihi. These deaths were attributed to infections with either Plasmodium spp. lineage LINN1 or P. relictum lineage GRW4. To the authors’ knowledge, this is the first published report of Plasmodium spp. infection in great spotted and brown kiwi, kereru and kokako. Currently, we are only able to speculate on the origin of these 14 isolates but consideration must be made as to the impact they may have on threatened endemic species, particularly due to the examples of mortality.     

Detection of malaria infection in blood transfusion: a comparative study among real-time PCR, rapid diagnostic test and microscopy: sensitivity of Malaria detection methods in blood transfusion

The transmission of malaria by blood transfusion was one of the first transfusion-transmitted infections recorded in the world. Transfusion-transmitted malaria may lead to serious problems because infection with Plasmodium falciparum may cause rapidly fatal death. This study aimed to compare real-time polymerase chain reaction (real-time PCR) with rapid diagnostic test (RDT) and light microscopy for the detection of Plasmodium spp. in blood transfusion, both in endemic and non-endemic areas of malaria disease in Iran. Two sets of 50 blood samples were randomly collected. One set was taken from blood samples donated in blood bank of Bandar Abbas, a city located in a malarious-endemic area, and the other set from Tehran, a non-endemic one. Light microscopic examination on both thin and thick smears, RDTs, and real-time PCR were performed on the blood samples and the results were compared. Thin and thick light microscopic examinations of all samples as well as RDT results were negative for Plasmodium spp. Two blood samples from endemic area were positive only with real-time PCR. It seems that real-time PCR as a highly sensitive method can be helpful for the confirmation of malaria infection in different units of blood transfusion organization especially in malaria-endemic areas where the majority of donors may be potentially infected with malaria parasites.     

The role of BAFF in immune function and implications for autoimmunity

Summary: BAFF [B‐cell activating factor belonging to the tumor necrosis factor (TNF) family] is a ligand that is required for peripheral B‐cell survival and homeostasis. In addition to mediating B‐cell survival, BAFF also regulates expression of certain B‐cell‐surface proteins, such as CD21/35. BAFF deficiency results in a reduced number of peripheral B cells and a diminished ability to mount robust humoral immune responses. Overexpression of BAFF has been linked to murine and human autoimmunity, and recent data provide clues as to how excess BAFF may allow the emergence of autoreactive B cells. In vivo animal testing with BAFF inhibitors has generated exciting data that support the pathway as a target for modulating B cells. The role of BAFF in B‐cell biology, T‐cell biology, and autoimmunity is discussed, as well as current efforts to develop BAFF inhibitors for clinical testing in autoimmune disorders.     

Protection of Batf3-deficient mice from experimental cerebral malaria correlates with impaired cytotoxic T-cell responses and immune regulation

Excessive inflammatory immune responses during infections with Plasmodium parasites are responsible for severe complications such as cerebral malaria (CM) that can be studied experimentally in mice. Dendritic cells (DCs) activate cytotoxic CD8⁺ T-cells and initiate immune responses against the parasites. Batf3^−/− mice lack a DC subset, which efficiently induces strong CD8 T-cell responses by cross-presentation of exogenous antigens. Here we show that Batf3^−/− mice infected with Plasmodium berghei ANKA (PbA) were protected from experimental CM (ECM), characterized by a stable blood−brain barrier (BBB) and significantly less infiltrated peripheral immune cells in the brain. Importantly, the absence of ECM in Batf3^−/− mice correlated with attenuated responses of cytotoxic T-cells, as their parasite-specific lytic activity as well as the production of interferon gamma and granzyme B were significantly decreased. Remarkably, spleens of ECM-protected Batf3^−/− mice had elevated levels of regulatory immune cells and interleukin 10. Thus, protection from ECM in PbA-infected Batf3^−/− mice was associated with the absence of strong CD8⁺ T-cell activity and induction of immunoregulatory mediators and cells.     

Role of IL‐10‐producing regulatory B cells in control of cerebral malaria in Plasmodium berghei infected mice

Cerebral malaria (CM) is a neurological syndrome often occurring in severe malaria. Although CM is known as an immunopathology in brain tissue mediated by excessive proinflammatory cytokines, the immunoregulatory mechanism is poorly understood. Here, we investigated the role of IL‐10‐producing regulatory B (Breg) cells in modulating CM development in a murine model of Plasmodium berghei ANKA infection. We observed that blood‐stage P. berghei induced expansion of IL‐10‐producing Breg cells in C57BL/6 mice. Adoptive transfer of IL‐10⁺ Breg cells to P. berghei infected mice significantly reduced the accumulation of NK and CD8⁺ T cells and hemorrhage in brain tissue, and improved the survival of the mice compared with control groups, although parasitemia levels were not altered. Treatment of Breg‐cell recipient mice with anti‐IL‐10 receptor mAb blocked the protective effect of Breg cells. Adoptive transfer of CD4⁺CD25⁺ Treg cells failed to prevent CM in infected mice. Spleen cells from Breg‐cell recipient mice produced increased levels of IL‐10 in vitro. Cell co‐culture showed that purified IL‐10⁺ B cells, but not IL‐10^? B cells, promoted IL‐10 production by CD4⁺ T cells. These results demonstrate that IL‐10‐producing Breg cells may represent an important mechanism for controlling the immunopathology and prevention of CM associated with P. berghei infection.     

Altered BAFF‐receptor signaling and additional modifier loci contribute to systemic autoimmunity in A/WySnJ mice

Systemic lupus erythematosus pathology reflects autoantibody‐mediated damage due to a failure of B‐lymphocyte tolerance. We previously reported that B‐lymphopenic A/WySnJ mice develop a lupus‐like syndrome and linked this syndrome to the B‐cell maturation defect‐1 (Bcmd‐1) mutant allele of the B‐cell‐activating factor belonging to the TNF family‐receptor (Baffr) gene. Here, we further evaluate the genetic basis for autoimmunity in A/WySnJ mice. We produced B6.Bcmd‐1 and AW.Baffr^?/? congenic mice (N5), and compared them with B6.Baffr^?/? and A/WySnJ mice with respect to B‐lymphocyte development. Bcmd‐1‐expressing mice had more B cells with greater maturity than Baffr^?/? mice regardless of genetic background, indicating that Bcmd‐1 encodes a partially functional BAFF‐R. We also compared these mice for lupus phenotypes to determine whether Bcmd‐1 is necessary and sufficient for disease, or whether the Baffr^?/?‐ allele can also cause autoimmunity. The Baffr^?/? allele did not lead to autoimmunity on either genetic background. In contrast, the Bcmd‐1 allele was necessary and sufficient for development of low levels of IgM autoantibodies in B6.Bcmd‐1 mice. However, Bcmd‐1 plus unidentified A/WySnJ modifier genes were necessary for development of IgG autoantibodies and renal pathology. We propose that in A/WySnJ mice an excess of BAFF per B cell rescues self‐reactive B cells through a partially functional BAFF‐R in a B‐lymphopenic environment.     

The NIK of time for B cells

NF‐κB‐inducing kinase (NIK) is a key mediator of the noncanonical NF‐κB signaling pathway, which is critical for B‐cell development and function. Although complete deletion of NIK in mice has been shown to result in defective B cells and impaired secondary lymphoid organogenesis, the consequences of deleting NIK exclusively in B cells have not been determined. In this issue of the European Journal of Immunology, Hahn et al. [Eur. J. Immunol. 2016. 46: 732–741] describe mice in which the NF‐κB2 pathway mediator, NIK, is deleted at different points in B‐cell lineage differentiation and activation. The results show that the survival of mature peripheral B cells, as well as appropriate kinetics of germinal center reactions, rely on noncanonical NF‐κB signaling. These findings confirm and extend prior observations implicating a nonredundant role for NF‐κB2 downstream of BAFF signaling via BAFF‐R, and prompt assessment of the growing literature regarding the relative roles of BCR and BAFF signals in B‐cell homeostasis, as well as the downstream pathways responsible.     

Supplementation of CXCL12 (CXCL12) induces homing of CD11c+ dendritic cells to the spleen and enhances control of Plasmodium berghei malaria in BALB/c mice

In malaria, parasitaemia is controlled in the spleen, a multicomponent organ that undergoes changes in its cellular constituents to control the parasite. During this process, dendritic cells (DCs) orchestrate the positioning of effector cells in a timely manner for optimal parasite clearance. We have recently demonstrated that CXCL12 [stromal cell‐derived factor‐1 (CXCL12)] supplementation partially restores the ability to control parasitaemia in Plasmodium berghei‐infected mice. In the present study, we investigated the nature of the DCs involved by flow cytometry and immunohistochemistry of CD11c⁺ cells. Flow cytometry of bone marrow cells showed that infection with P. berghei did not alter the proportion of CD11c⁺ cells present in this haematopoietic compartment, while CXCL12 supplementation of naïve uninfected mice induced only minor increases in the population of CD11c⁺ cells. In the spleen, P. berghei infection alone resulted in an increase in CD11c⁺ cells as compared with naïve animals. Exogenously administered CXCL12 in the absence of infection resulted in a significant expansion of the splenic CD11c⁺ population, and this effect was even more pronounced in infected and supplemented mice. Immunohistochemistry revealed that CD11c⁺ cells infiltrated the perivascular areas and marginal zone of the spleen in infected animals treated with CXCL12, suggesting that this chemokine induces homing of CD11c⁺ dendritic cells to the splenic compartment. Our results show that small amounts of CXCL12 supplementation are effective in recruiting DCs to the spleens of both uninfected and infected mice, suggesting the participation of CXCL12 and CD11c⁺ cells in the establishment of an adequate environment in the spleen for malaria control.     

Virulence‐dependent induction of interleukin‐10‐producing‐tolerogenic dendritic cells by Mycobacterium tuberculosis impedes optimal T helper type 1 proliferation

Mycobacterium tuberculosis inhibits optimal T helper type 1 (Th1) responses during infection. However, the precise mechanisms by which virulent M. tuberculosis limits Th1 responses remain unclear. Here, we infected dendritic cells (DCs) with the virulent M. tuberculosis strain H37Rv or the attenuated strain H37Ra to investigate the phenotypic and functional alterations in DCs and resultant T‐cell responses. H37Rv‐infected DCs suppressed Th1 responses more strongly than H37Ra‐infected DCs. Interestingly, H37Rv, but not H37Ra, impaired DC surface molecule expression (CD80, CD86 and MHC class II) due to prominent interleukin‐10 (IL‐10) production while augmenting the expression of tolerogenic molecules including PD‐L1, CD103, Tim‐3 and indoleamine 2,3‐dioxygenase on DCs in a multiplicity‐of‐infection (MOI) ‐dependent manner. These results indicate that virulent M. tuberculosis drives immature DCs toward a tolerogenic phenotype. Notably, the tolerogenic phenotype of H37Rv‐infected DCs was blocked in DCs generated from IL‐10^−/− mice or DCs treated with an IL‐10‐neutralizing monoclonal antibody, leading to restoration of Th1 polarization. These findings suggest that IL‐10 induces a tolerogenic DC phenotype. Interestingly, p38 mitogen‐activated protein kinase (MAPK) activation predominantly mediates IL‐10 production; hence, H37Rv tends to induce a tolerogenic DC phenotype through expression of tolerogenic molecules in the p38 MAPK–IL‐10 axis. Therefore, suppressing the tolerogenic cascade in DCs is a novel strategy for stimulating optimal protective T‐cell responses against M. tuberculosis infection.     

Effects of type I interferons in malaria

Type I interferons (IFNs) are a family of cytokines with a wide range of biological activities including anti‐viral and immune‐regulatory functions. Here, we focus on the protozoan parasitic disease malaria, and examine the effects of type I IFN‐signalling during Plasmodium infection of humans and experimental mice. Since the 1960s, there have been many studies in this area, but a simple explanation for the role of type I IFN has not emerged. Although epidemiological data are consistent with roles for type I IFN in influencing malaria disease severity, functional proof of this remains sparse in humans. Several different rodent‐infective Plasmodium species have been employed in in vivo studies of parasite‐sensing, experimental cerebral malaria, lethal malaria, liver‐stage infection, and adaptive T‐cell and B‐cell immunity. A range of different outcomes in these studies suggests a delicately balanced, multi‐faceted and highly complex role for type I IFN‐signalling in malaria. This is perhaps unsurprising given the multiple parasite‐sensing pathways that can trigger type I IFN production, the multiple isoforms of IFN‐α/β that can be produced by both immune and non‐immune cells, the differential effects of acute versus chronic type I IFN production, the role of low level ‘tonic’ type I IFN‐signalling, and that signalling can occur via homodimeric IFNAR1 or heterodimeric IFNAR1/2 receptors. Nevertheless, the data indicate that type I IFN‐signalling controls parasite numbers during liver‐stage infection, and depending on host–parasite genetics, can be either detrimental or beneficial to the host during blood‐stage infection. Furthermore, type I IFN can promote cytotoxic T lymphocyte immune pathology and hinder CD4⁺ T helper cell‐dependent immunity during blood‐stage infection. Hence, type I IFN‐signalling plays highly context‐dependent roles in malaria, which can be beneficial or detrimental to the host.     

BAFF regulates activation of self‐reactive T cells through B‐cell dependent mechanisms and mediates protection in NOD mice

Targeting the BAFF/APRIL system has shown to be effective in preventing T‐cell dependent autoimmune disease in the NOD mouse, a spontaneous model of type 1 diabetes. In this study we generated BAFF‐deficient NOD mice to examine how BAFF availability would influence T‐cell responses in vivo and the development of spontaneous diabetes. BAFF‐deficient NOD mice which lack mature B cells, were protected from diabetes and showed delayed rejection of an allogeneic islet graft. Diabetes protection correlated with a failure to expand pathogenic IGRP‐reactive CD8⁺ T cells, which were maintained in the periphery at correspondingly low levels. Adoptive transfer of IGRP‐reactive CD8⁺ T cells with B cells into BAFF‐deficient NOD mice enhanced IGRP‐reactive CD8⁺ T‐cell expansion. Furthermore, when provoked with cyclophosphamide, or transferred to a secondary lymphopenic host, the latent pool of self‐reactive T cells resident in BAFF‐deficient NOD mice could elicit beta cell destruction. We conclude that lack of BAFF prevents the procurement of B‐cell‐dependent help necessary for the emergence of destructive diabetes. Indeed, treatment of NOD mice with the BAFF‐blocking compound, BR3‐Fc, resulted in a delayed onset and reduced incidence of diabetes.     

A retrospective survey into the presence of Plasmodium spp. and Toxoplasma gondii in archived tissue samples from New Zealand raptors: New Zealand falcons (Falco novaeseelandiae), Australasian harriers (Circus approximans) and moreporks (Ninox novaeseelandiae)

Human colonisation of New Zealand has resulted in the introduction of emerging diseases, such as avian malaria and toxoplasmosis, which arrived with their exotic avian and mammalian hosts. Plasmodium spp. and Toxoplasma gondii have a wide host range, and several species of endemic New Zealand birds have developed a fatal disease following infection with either pathogen. However, no reports of either toxoplasmosis or avian malaria in New Zealand raptors, namely, the New Zealand falcons (Falco novaeseelandiae), Australasian harriers (Circus approximans) and moreporks (Ninox novaeseelandiae) exist in the literature. Therefore, this study was designed to determine if these two pathogens are present in these raptors through a retrospective analysis of archived tissue samples. Detection and isolate identification of these pathogens was determined using established histological and molecular techniques. All three species of New Zealand raptors tested positive for the presence of Plasmodium spp. (10/117; 8.5%) and an atypical genotype of T. gondii (9/117; 7.7%). Plasmodium lineages identified include P. elongatum GRW6, P. relictum SGS1, P. relictum PADOM02 and Plasmodium sp. LINN1. Two Australasian harriers and one morepork tested positive for the presence of both Plasmodium spp. and T. gondii. However, the pathogenicity of these organisms to the raptors is unclear as none of the tissues showed histological evidence of clinical disease associated with Plasmodium spp. and T. gondii infections. Thus, these results demonstrate for the first time that these two potential pathogens are present in New Zealand’s raptors; however, further research is required to determine the prevalence and pathogenicity of these organisms among the living populations of these birds in the country.