Enhancing durability of CIS43 monoclonal antibody by Fc mutation or AAV delivery for malaria prevention

CIS43 is a potent neutralizing human mAb that targets a highly conserved "junctional" epitope in the Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP). Enhancing the durability of CIS43 in vivo will be important for clinical translation. Here, 2 approaches were used to improve the durability of CIS43 in vivo while maintaining potent neutralization. First, the Fc domain was modified with the LS mutations (CIS43LS) to increase CIS43 binding affinity for the neonatal Fc receptor (FcRn). CIS43LS and CIS43 showed comparable in vivo protective efficacy. CIS43LS had 9- to 13-fold increased binding affinity for human (6.2 nM versus 54.2 nM) and rhesus (25.1 nM versus 325.8 nM) FcRn at endosomal pH 6.0 compared with CIS43. Importantly, the half-life of CIS43LS in rhesus macaques increased from 22 days to 39 days compared with CIS43. The second approach for sustaining antibody levels of CIS43 in vivo is through adeno-associated virus (AAV) expression. Mice administered once with AAV-expressing CIS43 had sustained antibody levels of approximately 300 μg/mL and mediated protection against sequential malaria challenges up to 36 weeks. Based on these data, CIS43LS has advanced to phase I clinical trials, and AAV delivery provides a potential next-generation approach for malaria prevention.

Application of system dynamics and participatory spatial group model building in animal health: A case study of East Coast Fever interventions in Lundazi and Monze districts of Zambia

East Coast Fever (ECF) is the most economically important production disease among traditional beef cattle farmers in Zambia. Despite the disease control efforts by the government, donors, and farmers, ECF cases are increasing. Why does ECF oscillate over time? Can alternative approaches such as systems thinking contribute solutions to the complex ECF problem, avoid unintended consequences, and achieve sustainable results? To answer these research questions and inform the design and implementation of ECF interventions, we qualitatively investigated the influence of dynamic socio-economic, cultural, and ecological factors. We used system dynamics modelling to specify these dynamics qualitatively, and an innovative participatory framework called spatial group model building (SGMB). SGMB uses participatory geographical information system (GIS) concepts and techniques to capture the role of spatial phenomenon in the context of complex systems, allowing stakeholders to identify spatial phenomenon directly on physical maps and integrate such information in model development. Our SGMB process convened focus groups of beef value chain stakeholders in two distinct production systems. The focus groups helped to jointly construct a series of interrelated system dynamics models that described ECF in a broader systems context. Thus, a complementary objective of this study was to demonstrate the applicability of system dynamics modelling and SGMB in animal health. The SGMB process revealed policy leverage points in the beef cattle value chain that could be targeted to improve ECF control. For example, policies that develop sustainable and stable cattle markets and improve household income availability may have positive feedback effects on investment in animal health. The results obtained from a SGMB process also demonstrated that a “one-size-fits-all” approach may not be equally effective in policing ECF in different agro-ecological zones due to the complex interactions of socio-ecological context with important, and often ignored, spatial patterns.

Specific Cell Targeting Therapy Bypasses Drug Resistance Mechanisms in African Trypanosomiasis

African trypanosomiasis is a deadly neglected disease caused by the extracellular parasite Trypanosoma brucei. Current therapies are characterized by high drug toxicity and increasing drug resistance mainly associated with loss-of-function mutations in the transporters involved in drug import. The introduction of new antiparasitic drugs into therapeutic use is a slow and expensive process. In contrast, specific targeting of existing drugs could represent a more rapid and cost-effective approach for neglected disease treatment, impacting through reduced systemic toxicity and circumventing resistance acquired through impaired compound uptake. We have generated nanoparticles of chitosan loaded with the trypanocidal drug pentamidine and coated by a single domain nanobody that specifically targets the surface of African trypanosomes. Once loaded into this nanocarrier, pentamidine enters trypanosomes through endocytosis instead of via classical cell surface transporters. The curative dose of pentamidine-loaded nanobody-chitosan nanoparticles was 100-fold lower than pentamidine alone in a murine model of acute African trypanosomiasis. Crucially, this new formulation displayed undiminished in vitro and in vivo activity against a trypanosome cell line resistant to pentamidine as a result of mutations in the surface transporter aquaglyceroporin 2. We conclude that this new drug delivery system increases drug efficacy and has the ability to overcome resistance to some anti-protozoal drugs.

Using microdialysis to analyse the passage of monovalent nanobodies through the blood-brain barrier

BACKGROUND AND PURPOSE

Nanobodies are promising antigen-binding moieties for molecular imaging and therapeutic purposes because of their favourable pharmacological and pharmacokinetic properties. However, the capability of monovalent nanobodies to reach targets in the CNS remains to be demonstrated.

EXPERIMENTAL APPROACH

We have assessed the blood-brain barrier permeability of Nb_An33, a nanobody against the Trypanosoma brucei brucei variant-specific surface glycoprotein (VSG). This analysis was performed in healthy rats and in rats that were in the encephalitic stage of African trypanosomiasis using intracerebral microdialysis, single photon emission computed tomography (SPECT) or a combination of both methodologies. This enabled the quantification of unlabelled and (99m) Tc-labelled nanobodies using, respectively, a sensitive VSG-based nanobody-detection elisa, radioactivity measurement in collected microdialysates and SPECT image analysis.

KEY RESULTS

The combined read-out methodologies showed that Nb_An33 was detected in the brain of healthy rats following i.v. injection, inflammation-induced damage to the blood-brain barrier, as in the late encephalitic stage of trypanosomiasis, significantly increased the efficiency of passage of the nanobody through this barrier. Complementing SPECT analyses with intracerebral microdialysis improved analysis of brain disposition. There is clear value in assessing penetration of the blood-brain barrier by monovalent nanobodies in models of CNS inflammation. Our data also suggest that rapid clearance from blood might hamper efficient targeting of specific nanobodies to the CNS.

CONCLUSIONS AND IMPLICATIONS

Nanobodies can enter the brain parenchyma from the systemic circulation, especially in pathological conditions where the blood-brain barrier integrity is compromised.

Antibodies fused to innate immune molecules reduce initiation of Cryptosporidium parvum infection in mice

At present no completely effective treatments are available for Cryptosporidium parvum infections in humans and livestock. Based on previous data showing the neutralizing potential of a panel of monoclonal antibodies developed against C. parvum, and based on the fact that innate immune peptides and enzymes have anticryptosporidial activity, we engineered several of these antibodies into antibody-biocide fusion proteins. We hypothesized that the combination of high-affinity antibody targeting with innate immune molecule-mediated killing would result in a highly effective new antiprotozoal agent. To test this hypothesis, we expressed antibody-biocide fusion proteins in a mammalian cell culture system and used the resulting products for in vitro and in vivo efficacy experiments. Antibody-biocide fusion proteins efficiently bound to, and destroyed, C. parvum sporozoites in vitro through a membrane-disruptive mechanism. When antibody-biocide fusion proteins were administered orally to neonatal mice in a prophylactic model of cryptosporidiosis, the induction of infection was reduced by as much as 81% in the mucosal epithelium of the gut, as determined on the basis of histopathological scoring of infectious stages. Several versions of antibody fusion proteins that differed in antigen specificity and in the biocide used had strong inhibitory effects on the initiation of infection. The results lay the groundwork for the development of a new class of antimicrobials effective against Cryptosporidium.

Ligation of B and T lymphocyte attenuator prevents the genesis of experimental cerebral malaria

B and T lymphocyte attenuator (BTLA; CD272) is a coinhibitory receptor that is predominantly expressed on T and B cells and dampens T cell activation. In this study, we analyzed the function of BTLA during infection with Plasmodium berghei ANKA. Infection of C57BL/6 mice with this strain leads to sequestration of leukocytes in brain capillaries that is associated with a pathology resembling cerebral malaria in humans. During the course of infection, we found an induction of BTLA in several organs, which was either due to up-regulation of BTLA expression on T cells in the spleen or due to infiltration of BTLA-expressing T cells into the brain. In the brain, we observed a marked induction of BTLA and its ligand herpesvirus entry mediator during cerebral malaria, which was accompanied by an accumulation of predominantly CD8+ T cells, but also CD4+ T cells. Application of an agonistic anti-BTLA mAb caused a significantly reduced incidence of cerebral malaria compared with control mice. Treatment with this Ab also led to a decreased number of T cells that were sequestered in the brain of P. berghei ANKA-infected mice. Our findings indicate that BTLA-herpesvirus entry mediator interactions are functionally involved in T cell regulation during P. berghei ANKA infection of mice and that BTLA is a potential target for therapeutic interventions in severe malaria.

Inhibition of 19-kDa C-terminal region of merozoite surface protein-1-specific antibody responses in neonatal pups by maternally derived 19-kDa C-terminal region of merozoite surface protein-1-specific antibodies but not whole parasite-specific antibodies

Immunizing pregnant women with a malaria vaccine is one approach to protecting the mother and her offspring from malaria infection. However, specific maternal Abs generated in response to vaccination and transferred to the fetus may interfere with the infant's ability to respond to the same vaccine. Using a murine model of malaria, we examined the effect of maternal 19-kDa C-terminal region of merozoite surface protein-1 (MSP1(19)) and Plasmodium yoelii Abs on the pups' ability to respond to immunization with MSP1(19). Maternal MSP1(19)-specific Abs but not P. yoelii-specific Abs inhibited Ab production following MSP1(19) immunization in 2-wk-old pups. This inhibition was correlated with the amount of maternal MSP1(19) Ab present in the pup at the time of immunization and was due to fewer specific B cells. Passively acquired Ab most likely inhibited the development of an Ab response by blocking access to critical B cell epitopes. If a neonate's ability to respond to MSP1(19) vaccination depends on the level of maternal Abs present at the time of vaccination, it may be necessary to delay immunization until Abs specific for the vaccinating Ag have decreased.

Inhibitory effect of antiserum to surface antigen P50 of Babesia gibsoni on growth of parasites in severe combined immunodeficiency mice given canine red blood cells

The inhibitory effect of an antiserum to surface protein P50 of Babesia gibsoni on the growth of the parasite was determined with severe combined immunodeficiency mice given canine red blood cells. The antiserum to the recombinant P50 protein significantly inhibited the parasite growth, indicating that P50 might be a useful vaccine candidate.

Type 1 immunity provides optimal protection against both mucosal and systemic Trypanosoma cruzi challenges

Chagas' disease results from infection with Trypanosoma cruzi, a protozoan parasite that establishes systemic intracellular infection after mucosal invasion. We hypothesized that ideal vaccines for mucosally invasive, intracellular pathogens like T. cruzi should induce mucosal type 2 immunity for optimal induction of protective secretory immunoglobulin A (IgA) and systemic type 1 immunity protective against intracellular replication. However, differential mucosal and systemic immune memory could be difficult to induce because of reciprocal inhibitory actions between type 1 and type 2 responses. To test our hypotheses, we investigated the protective effects of type 1 and type 2 biased vaccines against mucosal and systemic T. cruzi challenges. Intranasal vaccinations were given with recombinant interleukin-12 (IL-12)- and IL-4-neutralizing antibody (Ab) for type 1 immune bias, or recombinant IL-4 and gamma interferon-neutralizing Ab for type 2 immune bias. Cytokine RNA and protein studies confirmed that highly polarized memory immune responses were induced by our vaccination protocols. Survival after virulent subcutaneous T. cruzi challenge was used to assess systemic protection. Mucosal protection was assessed by measuring the relative inhibition of parasite replication in mucosal tissues early after oral T. cruzi challenge, using both PCR and quantitative culture techniques. As expected, only type 1 responses protected against systemic challenges (P < 0.01). However, contrary to our original hypothesis, type 1 responses optimally protected against mucosal challenges as well (P < 0.05). Type 1 and type 2 biased vaccines induced similar secretory IgA responses. We conclude that future vaccines for T. cruzi and possibly other mucosally invasive, intracellular pathogens should induce both mucosal and systemic type 1 immunity.

A critical role of Fc receptor-mediated antibody-dependent phagocytosis in the host resistance to blood-stage Plasmodium berghei XAT infection

Plasmodium berghei XAT is an irradiation-induced attenuated variant derived from the lethal strain P. berghei NK65, and its blood-stage parasites are spontaneously cleared in immune competent mice. In the present study, we studied the mechanism of host resistance to blood-stage malaria infection using P. berghei XAT. Infection enhanced Ab-dependent phagocytosis of PRBC by splenic macrophages in wild-type C57BL/6 mice. In contrast, FcR gamma-chain knockout (FcRgamma(-/-)) mice, which lack the ability to mediate Ab-dependent phagocytosis and Ab-dependent cell-mediated cytotoxicity through FcgammaRI, FcgammaRII, and FcgammaRIII, could not induce Ab-dependent phagocytic activity. These FcRgamma(-/-) mice showed increased susceptibility to the P. berghei XAT infection, with eventually fatal results, although they produced comparable amounts of IFN-gamma by spleen cells and anti-XAT Abs in serum. In addition, passive transfer of anti-XAT IgG obtained from wild-type mice that had recovered from infection into FcRgamma(-/-) mice could not suppress the increase in parasitemia, and almost all of these mice died after marked parasitemia. In contrast, passive transfer of anti-XAT IgG into control wild-type mice inhibited the increase in parasitemia. IFN-gamma(-/-) mice, which were highly susceptible to the P. berghei XAT infection, failed to induce Ab-dependent phagocytic activity and also showed reduced production of serum anti-XAT IgG2a isotype compared with control wild-type mice. These results suggest that FcR-mediated Ab-dependent phagocytosis, which is located downstream of IFN-gamma production, is important as an effector mechanism to eliminate PRBC in blood-stage P. berghei XAT infection.

Human malaria in immunocompromised mice: an in vivo model to study defense mechanisms against Plasmodium falciparum

We have recently described that sustained Plasmodium falciparum growth could be obtained in immunodeficient mice. We now report the potential of this new mouse model by assaying the effect of the passive transfer of antibodies (Abs) which in humans have had a well-established effect.Our results show that the total African adult hyperimmune immunoglobulin Gs (HI-IgGs) strongly reduce P. falciparum parasitemia similarly to that reported in humans, but only when mice are concomitantly reconstituted with human monocytes (HuMNs). In contrast, neither HI-IgGs nor HuMNs alone had any direct effect upon parasitemia. We assessed the in vivo effect of epitope-specific human Abs affinity-purified on peptides derived either from the ring erythrocyte surface antigen (RESA) or the merozoite surface protein 3 (MSP3). The inoculation of low concentrations of anti-synthetic peptide from MSP3, but not of anti-RESA Abs, consistently suppressed P. falciparum in the presence of HuMNs. Parasitemia decrease was stronger and faster than that observed using HI-IgGs and as fast as that induced by chloroquine. Our observations demonstrate that this mouse model is of great value to evaluate the protective effect of different Abs with distinct specificity in the same animal, a step hardly accessible and therefore never performed before in humans.

Immunodulation of rat serum and mucosal antibody responses to Entamoeba histolytica trophozoites by beta-1,3-glucan and cholera toxin

Systemic and mucosal and immune responses can be manipulated with immunomodulators. Here we show the modulatory effects of cholera toxin (CT) and beta-1,3-glucan (GLU) on the rat antiamebic serum and fecal antibody responses to one or four intraperitoneal (IP) or intragastric (IG) doses of glutaraldehyde-fixed Entamoeba histolytica trophozoites (GFT). One IP dose of GFT maximized serum IgM and IgG antiamebic antibodies on days 4 and 9, respectively; CT coadministration increased IgM antibodies, whereas IgG titers increased with CT or GLU; coproantibodies were undetectable after GFT alone or coadministered with GLU, whereas CT coadministration maximized fecal IgA antibodies on day 6. One IG dose of GFT alone increased serum IgM and IgG antibodies 2.5 times and no further increases were detected using GLU, whereas CT doubled serum IgG antibodies; GFT did not affect the coproantibody responses, whereas GLU coadministration maximized IgG coproantibody levels on day 6 and CT increased IgG and IgA coproantibody levels on the same day. On the other hand, four IG doses of GFT alone or with GLU induced tolerance, whereas GFT alone via the IP route increased serum antibodies slightly and GLU coadministration increased serum IgG antibody titers 300-fold. CT coadministration by both routes increased IgA coproantibodies, and simultaneous CT+GLU coadministration induced lower responses than either CT or GLU. Different antiamebic immune responses might therefore be attained through the use of different immunization routes and immunomodulators to induce protective immunity against intestinal or extraintestinal amebiasis.

Antibodies against ribosomal phosphoprotein P0 of Plasmodium falciparum protect mice against challenge with Plasmodium yoelii

Antibodies against the Plasmodium falciparum P0 ribosomal phosphoprotein (PfP0) have been detected exclusively but extensively in malaria-immune persons. Polyclonal rabbit and mice sera were raised against two recombinant polypeptides of P. falciparum P0 protein, PfP0N and PfP0C, covering amino acids 17 to 61 and the remaining amino acids 61 to 316, respectively. Sera against both these domains detected a 35-kDa protein from Plasmodium yoelii subsp. yoelii, a rodent malarial parasite, and stained the surface of merozoites in immunofluorescence assays. Total immunoglobulin G (IgG) purified from rabbit and mouse anti-PfP0 sera by ammonium sulfate and DEAE-cellulose chromatography was used for passive transfer experiments in mice. Mice passively immunized with both anti-PfP0N and anti-PfP0C showed distinctly lower levels of parasitemia than control mice. With immunizations on days -1, 0, 1, 3, and 5, about 50% of both sets of mice receiving anti-PfP0N and anti-PfP0C cleared the lethal 17XL strain of P. yoelii and revived by day 25. All the control mice died by day 10. By extending the immunization schedule, the survival period of the mice could be extended for every mouse that received anti-PfP0 IgG. These data demonstrate the cross-protection of the anti-PfP0 IgG and establish parasite P0 protein as a target for invasion-blocking antibodies.

Internalization of Leishmania mexicana complex amastigotes via the Fc receptor is required to sustain infection in murine cutaneous leishmaniasis

We show here that maintenance of Leishmania infections with Leishmania mexicana complex parasites (Leishmania amazonensis and Leishmania pifanoi) is impaired in the absence of circulating antibody. In these studies, we used mice genetically altered to contain no circulating antibody, with and without functional B cells. This experimental design allowed us to rule out a critical role for B cell antigen presentation in Leishmania pathogenesis. In addition, we show that mice lacking the common gamma chain of Fc receptors (FcgammaRI, FcepsilonRI, and FcgammaRIII) are similarly refractory to infection with these parasites. These observations establish a critical role for antibody in the pathogenesis associated with infection by members of the L. mexicana complex.

Decreased resistance of B cell-deficient mice to infection with Toxoplasma gondii despite unimpaired expression of IFN-gamma, TNF-alpha, and inducible nitric oxide synthase

The role of B cells in resistance against Toxoplasma gondii was studied using B cell-deficient (muMT) mice. Following peroral infection with 10 cysts of the ME49 strain, all muMT mice survived the acute stage of the infection but died between 3 and 4 wk after infection. In contrast, all control mice were alive at 8 wk after infection. At the stage during which muMT animals succumbed to the infection, parasite replication and pathology were most evident in their brains; small numbers of tachyzoites were also detectable in their lungs. Significantly greater numbers of T. gondii cysts and areas of inflammation associated with tachyzoites were observed in brains of muMT than in control mice. Large areas of necrosis associated with numerous tachyzoites were observed only in brains of muMT mice. Anti-T. gondii IgG Abs were detected only in sera of control mice, whereas similar levels of IFN-gamma were detected in sera of both strains of mice. Amounts of mRNA for IFN-gamma, IL-10, and inducible NO synthase in the brain did not differ between infected muMT and control mice. Expression of mRNA for TNF-alpha was increased in brains of muMT mice. Administration of polyclonal rabbit anti-T. gondii IgG Ab prevented early mortality and pathology associated with tachyzoites in the brain in the infected muMT mice. These results indicate that B cells play an important role, most likely through their production of specific Abs, in resistance to persistent active (tachyzoite) infection with T. gondii in mice, especially in the brain and lung.

Self and nonself stimulatory molecules induce preferential expansion of CD5+ B cells or activated T cells of chagasic patients, respectively

It has previously been demonstrated that Trypanosoma cruzi-derived antigens (TRP) and human parasite-specific antibodies (Id) stimulate proliferation of cells from Chagasic patients. More recently, we have shown that activated T cells and CD5+ B cells are present in elevated levels in the peripheral blood of Chagasic patients. Upon in vitro exposure to these two different types of stimulatory molecules (TRP, Id), we now show that each of these elevated populations respond differentially to TRP or Id. We found that stimulation with TRP led to preferential expansion of activated T cells, while Id preferentially stimulated CD5+ B cells and CD8+ T cells. Moreover, this expansion of CD5+ B cells by Id was even more pronounced in cultures of cells from Chagasic patients with the severe, cardiac form of the disease, as compared to indeterminate patients. CD8+ T cells comprise approximately 50% of the total T cells in cultures stimulated by Id while in TRP-stimulated cultures their frequency is proportionally lower. Since parasite antigens and antiparasite antibodies are always present in the host during the chronic phase of the disease, they may also be involved with differential activation mechanisms of these cell populations in vivo.

Absolute requirement for an active immune response involving B cells and Th cells in immunity to Plasmodium yoelii passively acquired with antibodies to the 19-kDa carboxyl-terminal fragment of merozoite surface protein-1

Vaccination of mice with the leading malaria vaccine candidate homologue, the 19-kDa carboxyl terminus of merozoite surface protein-1 (MSP119), results in sterile immunity to Plasmodium yoelii, with no parasites detected in blood. Although such immunity depends upon high titer Abs at challenge, high doses of immune sera transferred into naive mice reduce parasitemia (and protect from death) but do not result in a similar degree of protection (with most mice experiencing high peak parasitemias); this finding suggests that ongoing parasite-specific immune responses postchallenge are essential. We analyzed this postchallenge response by transferring Abs into manipulated but malaria-naive mice and observed that Abs cannot protect SCID, nude, CD4+ T cell-depleted, or B cell knockout mice, with all mice dying. Thus, in addition to the Abs that develop following MSP119 vaccination, a continuing active immune response postchallenge is required for protection. MSP119-specific Abs can adoptively transfer protection to strains of mice that are not protected following vaccination with MSP119, suggesting that the Ags targeted by the immune response postchallenge include Ags apart from MSP119. These data have important implications for the development of a human malaria vaccine.

Role of immunoglobulin A monoclonal antibodies against P23 in controlling murine Cryptosporidium parvum infection

Cryptosporidium parvum is an important diarrhea-causing protozoan parasite of immunocompetent and immunocompromised hosts. Immunoglobulin A (IgA) has been implicated in resistance to mucosal infections with bacteria, viruses, and parasites, but little is known about the role of IgA in the control of C. parvum infection. We assessed the role of IgA during C. parvum infection in neonatal mice. IgA-secreting hybridomas were developed by using Peyer's patch lymphocytes from BALB/c mice which had been orally inoculated with viable C. parvum oocysts. Six monoclonal antibodies (MAbs) were selected for further study based on indirect immunofluorescence assay reactivity with sporozoite and merozoite pellicles and the antigen (Ag) deposited on glass substrate by gliding sporozoites. Each MAb was secreted in dimeric form and recognized a 23-kDa sporozoite Ag in Western immunoblots. The Ag recognized comigrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with P23, a previously defined neutralization-sensitive zoite pellicle Ag. MAbs were evaluated for prophylactic or therapeutic efficacy against C. parvum, singly and in combinations, in neonatal BALB/c mice. A combination of two MAbs given prophylactically prior to and 12 h following oocyst challenge reduced the number of intestinal parasites scored histologically by 21.1% compared to the numbers in mice given an isotype-matched control MAb (P < 0.01). Individual MAbs given therapeutically in nine doses over a 96-h period following oocyst challenge increased efficacy against C. parvum infection. Four MAbs given therapeutically each reduced intestinal infection 34.4 to 42.2% compared to isotype-matched control MAb-treated mice (P < 0.05). One MAb reduced infection 63.3 and 72. 7% in replicate experiments compared to isotype-matched control MAb-treated mice (P < 0.0001). We conclude that IgA MAbs directed to neutralization-sensitive P23 epitopes may have utility in passive immunization against murine C. parvum infection.

Expansion of IL-3-responsive IL-4-producing non-B non-T cells correlates with anemia and IL-3 production in mice infected with blood-stage Plasmodium chabaudi malaria

A prominent switch of CD4+ T cells from Th1 to Th2 type response occurs in mice infected with the non-lethal malaria parasite Plasmodium chabaudi chabaudi AS around the time of peak parasitemia. This is reflected by a decrease in IFN-gamma- and an increase in IL-4-producing cells. The peak occurs approximately 9-10 days after infection and is accompanied by anemia. The mechanism behind the switch in Th cell response is poorly understood. We here report on the production of IL-4 from a non-T cell source during P. chabaudi infection in BALB/c mice. Flow cytometric analysis of spleen and peripheral blood leukocytes (PBL) showed a dramatic increase in the percentage of non-B non-T (NBNT) cells 9-23 days after P. chabaudi infection with peak values by day 15 (approximately 30 % of splenocytes and approximately 55 % of PBL being NBNT cells). The expansion of NBNT cells correlated closely with the appearance of a cell type secreting IL-4 and IL-6 following stimulation with IL-3 and/or cross-linking of FcgammaR. Compared to cells from uninfected animals, NBNT cells from P. chabaudi-infected mice were shown to be hyper-responsive to IL-3. The levels of the hematopoietic cytokine IL-3 were elevated in supernatants from unstimulated spleen cell cultures as well as in serum at the same time points at which NBNT cell-derived IL-4 and IL-6 were detected from spleen cultures and PBL. Thus, IL-3-responsive IL-4-producing NBNT cells may provide cytokines supporting the switch from Th1 to a Th2 response which is important for the final clearance of the parasite in P. chabaudi malaria.

Gene-targeted mice lacking B cells are unable to eliminate a blood stage malaria infection

Mice deficient of mature B cells due to a targeted disruption of the transmembrane exon of the Ig mu-chain gene (mu-MT mice) can reduce a primary acute infection with the malaria parasite Plasmodium chabaudi chabaudi (AS strain) to low levels but are unable to eliminate parasites and instead develop chronic relapsing parasitemias. This model of B cell deficiency confirms previous findings using anti-mu-treated mice that B cells are required for final parasite clearance. Injection of B cells from immune donors into chronically infected mu-MT mice enabled them to clear their infection within 1 wk. When mu-MT mice that had been cured of their malaria infection by treatment with chloroquine were rechallenged with P. c. chabaudi (AS) they developed secondary infections of a magnitude similar to a primary infection, in contrast to wild-type mice in which a secondary challenge results only in a transient low patent parasitemia. These results suggest that B cell-dependent mechanisms play a crucial role in immunity to secondary infections. There is a pronounced expansion of gamma delta cells in the spleen of chronically infected mu-MT mice. After clearance of parasites in mu-MT mice either after adoptive transfer of immune B cells or by treatment with chloroquine, gamma delta T cells returned to levels observed in wild-type mice. This suggests that the expansion of gamma delta cells observed in mu-MT mice is due to the chronic persistence of parasites, rather than to the lack of B cells.

Transmission blocking antibody of the Plasmodium falciparum zygote/ookinete surface protein Pfs25 also influences sporozoite development

The Plasmodium falciparum zygote/ookinete surface protein, Pfs25, persists in the oocyst wall throughout its development. Anti-25 kD transmission blocking antibody, given to infected Anopheles stephensi or A. gambiae mosquitoes in an additional bloodmeal, 3-6 days after being fed gametocyte infected blood, penetrated the oocyst and reacted with the 25 kD protein within it. This reaction caused a significant reduction in the number of developing sporozoites. Mouse serum containing antibodies raised by immunization with a recombinant 25 kD yeast product showed a similar effect.

Hyperimmune hens as a novel source of anti-Cryptosporidium antibodies suitable for passive immune transfer

Leghorn hens were subcutaneously immunized with 25 micrograms of Cryptosporidium parvum oocyst emulsified in Freund's complete adjuvant. A booster dose was injected 5 weeks later. Anti-Cryptosporidium activities of yolks and sera measured by an enzyme-linked immunosorbent assay (ELISA), demonstrated high levels in both sera and egg yolks which persisted for at least 17 wk. Preparations from yolks with high, medium and low anti-Cryptosporidium ELISA activities were used in a neonatal mouse model to assess their biological activities. A significant parasite reduction (P less than or equal to 0.001) was found between the high and all other groups. Hyperimmune eggs could be used as a source for passive immunity in cryptosporidiosis.

Antibodies that protect humans against Plasmodium falciparum blood stages do not on their own inhibit parasite growth and invasion in vitro, but act in cooperation with monocytes

IgG extracted from the sera of African adults immune to malaria were injected intravenously into eight Plasmodium falciparum-infected nonimmune Thai patients. Clinical and parasitological improvement was reproducibly obtained in each case. After the disappearance of the transferred Ig, recrudescent parasites were equally susceptible to the same Ig preparation. High levels of antibodies to most parasite proteins were detected by Western blots in the receivers' sera (taken before transfer) as in the donors' Ig, thus indicating that the difference was qualitative rather than quantitative between donors and receivers. In vitro, the clinically effective Ig had no detectable inhibitory effect on either penetration or intra-erythrocytic development of the parasite. On the contrary, they sometimes increased parasite growth. In contrast, these IgG, as the receivers' Ig collected 4 d after transfer, but not those collected before transfer, proved able to exert an antibody-dependent cellular inhibitory (ADCI) effect in cooperation with normal blood monocytes. Results were consistent among the seven isolates studied in vitro, as with the recrudescent parasites. Thus, the results obtained in the ADCI assay correlate closely with clinical and parasitological observations.

Chagas' disease. Immunotoxin inhibition of Trypanosoma cruzi release from infected host cells in vitro

Virulent tissue culture-derived Trypanosoma cruzi trypomastigotes were readily killed by immune IgG-ricin A chain conjugates (ITR) in vitro. Forty micrograms of ITR immobilized 10(6) trypomastigotes after 48 hours of incubation at 37 degrees C. ITR showed antibody specificity and 125I-labeled anti-T. cruzi IgG bound to parasitized host cells 9-fold more than to nonparasitized host cells. The degree of specificity was evaluated further in experiments in which 10 micrograms of ITR showed 78% inhibition of [3H]thymidine incorporation by T. cruzi. In contrast, nonimmune IgG-ricin A chain conjugate neither immobilized nor inhibited [3H]thymidine incorporation by the parasite. Furthermore, 20 micrograms of ITR significantly inhibited T. cruzi trypomastigote release from infected host cells and thus prevented reinfection of other cells in vitro.

Experimental visceral leishmaniasis: role of endogenous IFN-gamma in host defense and tissue granulomatous response

The capacity of BALB/c mice to acquire resistance to and eliminate intracellular visceral Leishmania donovani is T cell dependent, associated with a granulomatous tissue reaction, and correlates with the ability to secrete the macrophage-activating lymphokine, IFN-gamma. These responses appear by 4 wk after infection and are fully established by 8 wk. To examine the role of endogenous IFN-gamma, BALB/c mice were injected with anti-IFN-gamma mAb before and for 8 wk after infection. At 4 wk, mAb treatment inhibited the acquisition of resistance to L. donovani and abolished mature granuloma formation. Although liver parasite burdens in mAb-treated mice were fivefold higher than in controls at 8 wk, continually treated mice nevertheless began for form tissue granulomas and decreased their parasite loads by 50% from peak values. The levels of anti-IFN-gamma antibody in the serum of mice injected for 8 wk were appreciably reduced, thus raising the possibilities of either insufficient neutralization of endogenous IFN-gamma at this time point or a pathway independent of IFN-gamma. Although the role of IFN-gamma and the potential effect of an IFN-gamma-independent mechanism in the resolution of visceral infection remain to be defined, these results indicate that IFN-gamma plays a critical role in the early immune response that both optimally controls L. donovani infection and induces the tissue granuloma.

Interdependence of CD4+ T cells and malarial spleen in immunity to Plasmodium vinckei vinckei. Relevance to vaccine development

We studied immunity to the blood stage of the rodent malaria, Plasmodium vinckei vinckei, which is uniformly lethal to mice. BALB/c mice develop solid immunity after two infections and drug cure. The following experiments define the basis of this immunity. Transfer of pooled serum from such immune mice renders very limited protection to BALB/c mice and no protection to athymic nu/nu mice. Moreover, B cell-deficient C3H/HeN mice develop immunity to P. vinckei reinfection in the same manner as immunologically intact mice, an observation made earlier. In vivo depletion of CD4+ T cells in immune mice abrogates their immunity. This loss of immunity could be reversed through reconstitution of in vivo CD4-depleted mice with fractionated B-, CD8-, CD4+ immune spleen cells; however, adoptive transfer of fractionated CD4+ T cells from immune spleen into naive BALB/c or histocompatible BALB/c nude mice does not render recipients immune. In vivo depletion of CD8+ T cells did not influence the parasitemia in nonimmune or immune mice. Splenectomy of immune mice completely reverses their immunity. Repletion of splenectomized mice with their own spleen cells does not reconstitute their immunity. We conclude that some feature of the malaria-modified spleen acts in concert with the effector/inducer function of CD4+ T cells to provide protection from P. vinckei. To be consistent with this finding, a malaria vaccine may require a combination of malaria Ag to induce immune CD4+ T cells and an adjuvant or other vaccine vehicle to alter the spleen.

Effects of immune colostrum and orally administered antisporozoite monoclonal antibodies on the outcome of Cryptosporidium parvum infections in neonatal mice

A neonatal BALB/c mouse model of cryptosporidiosis was used to examine the potential passive transfer of immunity via immune colostrum and oral treatment with anticryptosporidial monoclonal antibodies. Neonates suckled by dams that recovered from Cryptosporidium parvum infections were equally susceptible to infection as their control counterparts suckled by naive dams. Parasite loads among the control and immune colostrum-fed mice were indistinguishable. Neonates receiving orally administered antisporozoite monoclonal antibodies were equally susceptible to infections compared with the control and immune colostrum-fed mice. Parasite loads among the mice receiving daily oral treatment with monoclonal antibody mixtures exhibited significantly lower parasite loads compared with the control mice (P less than 0.05).

In-vitro exoerythrocytic development of Plasmodium cynomolgi bastianellii: inhibitory activity of monoclonal antibodies against sporozoites of different P. cynomolgi strains and of P. knowlesi

The inhibitory effect of anti-sporozoite monoclonal antibodies (MoAb) on the in-vitro development of liver stages of Plasmodium cynomolgi bastianellii (NIH strain) was evaluated using primary cultures of rhesus monkey hepatocytes. MoAbs against the circumsporozoite proteins of five strains of P. cynomolgi (NIH, London, Gombak, Ceylon, Berok), and of P. knowlesi (H strain) were used. Incubation of sporozoites of P. cynomolgi bastianellii with the anti-NIH strain MoAbs entirely prevented liver-stage development; MoAbs produced against the other four strains had no apparent activity. The anti-P. knowlesi MoAbs had a partially inhibitory effect on parasite development. These functional studies complement previous immunological studies on P. cynomolgi strain specificity, and confirm the cross-reactivity observed previously between sporozoites of P. cynomolgi bastianellii and P. knowlesi (H strain).

Plasmodium falciparum: administration of anti-sporozoite antibodies during sporogony results in production of sporozoites which are not neutralized by human anti-circumsporozoite protein vaccine sera

Five days after receiving a Plasmodium falciparum NF54 infectious blood meal, Anopheles stephensi mosquitoes were fed rat anti-P, falciparum sporozoite or rabbit anti-R32tet32 antibodies. Sporozoites isolated from salivary glands were tested by the inhibition of sporozoite invasion (ISI) assay using monoclonal antibody (Mab) 2A10 to P. falciparum circumsporozoite protein or sera from human volunteers immunized with P. falciparum R32tet32 or (NANP)3-TT vaccines. Whereas sporozoites from control mosquitoes were neutralized by Mab 2A10 and vaccine sera, only the Mab and not the vaccine sera neutralized sporozoites from immune-fed mosquitoes. The implications of these results in vaccine design and the impact on transmission are discussed.

Clinical and serological response after experimental inoculation with Babesia divergens of newborn calves with and without maternal antibodies

The influence of maternal antibodies on clinical and serological response after experimental inoculation with Babesia divergens of newborn calves was studied. Five calves, born to dams seropositive for B.divergens, (Group 1) had specific maternal antibodies when tested 12 h after their first feeding of colostrum. At that point they were inoculated i.v. with B.divergens infected erythrocytes. Five other calves, born to dams seronegative for B.divergens, (Group 2) had no Babesia specific maternal antibodies when inoculated at the same age.

Babesia divergens organisms were demonstrated in blood smears from calves in both groups at some point 5 to 10 days p.i. All calves in both groups had B.divergens specific IgM antibodies at 7 to 17 days p.i. as shown by a modified IF-test. Specific IgG antibodies, transferred by colostrum, were found in all calves of Group 1 before inoculation of B.divergens. The IgG titre of these animals increased by a doubling dilution step at 11–25 days p.i. Among calves of Group 2 specific IgG antibodies were found at first between day 9 and 15 p.i. Both IgM and IgG antibody titres had to be investigated since demonstrated IgG antibodies can originate both from maternally transferred antibodies and from actively produced antibodies after an infection.

There was no difference in clinical parameters; parasitaemia, PCV, Hb, and rectal temperature between the groups.

This experiment gives evidence that there can be a resistance to bovine babesiosis in newborn calves independent of maternal antibodies.