Attenuated vaccinia virus-circumsporozoite protein recombinants confer protection against rodent malaria.

NYVAC-based vaccinia virus recombinants expressing the circumsporozoite protein (CSP) were evaluated in the Plasmodium berghei rodent malaria model system. Immunization of mice with a NYVAC-based CSP recombinant elicited a high level of protection (60 to 100%). Protection did not correlate with CS repeat-specific antibody responses and was abrogated by in vivo CD8+ T-cell depletion. Protection was not enhanced by modification of the subcellular localization of CSP. These results suggest the potential of poxvirus-based vectors for the development of vaccine candidates for human malaria.     

Innate immune defense against malaria infection in the mosquito

Anopheles gambiae, the most important vector of malaria, employs its innate immune system in the fight against Plasmodium. This can affect the propagative capacity of Plasmodium in the vector and, in some cases, leads to total refractoriness to the parasite. The components operating in the mosquito's innate immune system and their potential relevance to antimalarial responses are being systematically dissected.     

Vaccination against malaria with live parasites

Despite nearly 80 years of vaccine research and control efforts, malaria remains one of the most prevalent of all infectious diseases. The fact that people living in regions in which malaria is endemic eventually develop immunity to the parasite and the disease suggest that it might be possible to develop vaccines against malaria. Although few vaccination trials were conducted with whole parasites, the only protocol that leads to the induction of sterile immunity in humans relies on immunization with attenuated parasites. This observation has spurred the search for subunit vaccines that aim to reproduce this protection. As yet, none of the current candidate subunit vaccines have achieved complete protection reproducibly. This failure, coupled with the recent advent of the genetically modified Plasmodium parasites, has led to a renewed interest in the use of live parasites for vaccination. This article reviews past studies, summarizes recent developments in this field and discusses the challenges to be overcome before mass immunization with live parasites could be envisaged.     

Mosquito immune responses against malaria parasites

Anopheline mosquitoes are the major vectors of human malaria. Mosquito-parasite interactions are a critical aspect of disease transmission and a potential target for malaria control. Mosquitoes vary in their innate ability to support development of the malaria parasite, but the molecular mechanisms that determine vector competence are poorly understood. This area of research has been revolutionized by recent advances in the mosquito genome characterization and by the development of new tools for functional gene analysis.     

Treatment of mosquito bites with cetirizine

Eighteen adult subjects sensitive to mosquito bites participated in a double-blind, placebo-controlled study with 10 mg cetirizine. The drug was given prophylactically and the subjects were then exposed to bites of Aedes communis mosquitoes in the field. Bite lesions were measured and pruritus was scored with a visual analogue scale at 15 min, 60 min, 12 hr and 24 hr. Cetirizine significantly decreased immediate wealing and pruritus and, interestingly, also had a clear effect on the delayed 12 hr and 24 hr bite papules and pruritus. The diameter of a 15 min mosquito-bite weal was 10.10 ± 10.10 mm (mean ±s.d.) with the placebo and 5.5 ± 5.5 mm with cetirizine treatment (P<0.0). The 15 min pruritus scores were 36.36 ± 25.25 and 11.11±13.13 (P< 0.0), respectively. The diameter of the 24 hr mosquito-bite lesion was 12.12 ± 21.21 mm with the placebo and 7.7±16.16 mm with cetirizine treatment (P<0.0). The 24 hr pruritus scores were 18.18 ± 25.25 and 6.6±14.14 (P<0.0), respectively. These results indicate that, in mosquito-sensitive subjects, prophylactically administered cetirizine is an effective drug against both immediate and delayed mosquito-bite symptoms.     

Virtual memory CD8 T cells expanded by helminth infection confer broad protection against bacterial infection

Epidemiological data and animal studies suggest that helminth infection exerts potent immunomodulatory effects that dampen host immunity against unrelated pathogens. Despite this notion, we unexpectedly discovered that prior helminth infection resulted in enhanced protection against subsequent systemic and enteric bacterial infection. A population of virtual memory CD8 T (CD8 T_VM) cells underwent marked expansion upon infection with the helminth Heligmosomoides polygurus by an IL-4-regulated, antigen-independent mechanism. CD8 T_VM cells disseminated to secondary lymphoid organs and established a major population of the systemic CD8 T cell pool. IL-4 production elicited by protein immunization or selective activation of natural killer T cells also results in the expansion of CD8 T_VM cells. Notably, CD8 T_VM cells expanded by helminth infection are sufficient to transfer innate non-cognate protection against bacteria to naïve animals. This innate non-cognate “collateral protection” mediated by CD8 T_VM might provide parasitized animals an advantage against subsequent unrelated infections, and represents a potential novel strategy for vaccination.     

A dichotomous role for nitric oxide in protection against blood stage malaria infection

Nitric oxide (NO) is cytotoxic and cytostatic to blood stage malaria parasites in vitro, but the precise mechanism(s) by which it mediates an effect in vivo is not known. In particular, whether or not control of acute parasitemia depends on the presence of NO is unclear. We have shown previously that blocking NO synthesis at the time of its induction may cause an increase in peak primary parasitemia during infection of mice with Plasmodium chabaudi, suggesting that NO may be parasiticidal in vivo. However, as recent data indicate that NO suppresses Th1 cell proliferation in vitro by downregulating IL-2 production, we have investigated whether this immunoregulatory function of NO affects its capacity for anti-malarial activity. Treatment of P. chabaudi-infected mice with the iNOS inhibitor aminoguanidine hemisulfate (AG) starting just prior to the peak of primary parasitemia caused a significant elevation and extension of the acute infection and led to a partial but significant abrogation of the suppression of spleen cell proliferation to both mitogen and specific antigen observed when NO synthesis was not blocked. In the absence of NO, levels of IL-2, but not of IFN-gamma, TNF-alpha, or of any Th2-regulated cytokines examined, increased significantly. However, when AG treatment was brought forward to the early ascending phase of primary parasitemia, significantly increased levels of IFN-gamma and TNF-alpha, as well as of IL-2, were observed over those for infected control mice similarly treated with phosphate-buffered saline. Moreover, despite the absence of NO, parasitemias of AG-treated mice were not significantly elevated. The effect of AG therefore appeared to be dependent upon the timing of its administration in vivo. We propose that during malaria infections, there is a dynamic balance between the regulatory and anti-parasitic roles of NO. While the immunosuppressive function of NO leads to a downregulation in vivo of production of IL-2, and indirectly of IFN-gamma and TNF-alpha, this perceived weakening of the host cell-mediated immune response is in part masked by the protective anti-malarial effects of NO itself.     

Cyclophosphamide pretreatment and protection against malaria.

Mice pretreated with cyclophosphamide were able to overcome infection from a lethal malarial strain. The development of resistance was preceded by increased hypersensitivity to malarial antigens. Hypersensitivity was demonstrable by a delayed footpad swelling technique.     

Protein/DNA vaccine-induced antigen-specific Treg confer protection against asthma

Asthma is a chronic inflammatory disorder caused by T-cell-mediated inflammation within airways. No antigen-specific treatment has been available. Using an OVA-induced murine asthma model, we find that co-immunization of an OVA epitope peptide with a DNA vaccine encoding the same epitope is able to prevent this experimental asthma as evidenced in the marked reduction of infiltrations of eosinophils and lymphocytes into the site of the allergen challenge. We demonstrate that the prevention of experimental asthma was directly related to the induction of a population of OVA-specific T-regulatory cells (Treg) exhibiting a CD4(+)CD25(-)FoxP3(+) phenotype and expressing IL-10, TGF-beta and IFN-gamma following the co-immunization. Blockade of IL-10 and TGF-beta of the Treg by anti-IL-10 and TGF-beta antibodies is partially able to reverse the suppression in vitro and in vivo, which caused the recurrence of the inflammation. Furthermore, adoptive transfer of the induced Treg is also able to suppress the OVA-induced asthma. To our knowledge, the combination of peptide with its cognate DNA vaccine protect experimental asthma via the induced epitope-specific Treg has not been previously reported and such strategy may lead to a novel immunotherapy against asthma in humans.     

Immune T cells sorted by flow cytometry confer protection against infection with Treponema pallidum subsp. pertenue in hamsters.

The role of cell-mediated immunity against infection with Treponema pallidum subsp. pertenue in humans or experimental animals is unclear. Hamsters injected subcutaneously in the hind paws with 4 x 10(6) unfractionated lymph node cells or enriched lymph node T cells (immunoglobulin negative, Ia negative) from T. pallidum subsp. pertenue-immune hamsters were resistant to challenge with T. pallidum subsp. pertenue. The popliteal lymph nodes of hamsters that received immune cells weighed less and had significantly fewer treponemes than did lymph nodes from hamsters infused with cells from nonimmune donors. Furthermore, recipients of immune T cells failed to develop antitreponemal antibodies 21 days after challenge. Enriched T cells were obtained by flow cytometric separation by using monoclonal anti-Ia antibody 14-4-4s, which identified hamster B cells. Flow cytometric analysis by two-color immunofluorescent staining with anti-hamster-immunoglobulin and monoclonal anti-Ia antibody 14-4-4s confirmed that monoclonal anti-Ia antibody 14-4-4s recognized B cells. In addition, lymph node cells obtained after treatment with anti-Ia monoclonal antibody 14-4-4s and complement were 97% T cells, as determined by monoclonal antibody 20, a hamster T-cell marker. These results demonstrated that highly enriched T cells (immunoglobulin negative, Ia negative) from T. pallidum subsp. pertenue-immune hamsters conferred partial protection on hamsters against infection with T. pallidum subsp. pertenue.     

Peptide-based subunit vaccines against pre-erythrocytic stages of malaria parasites.

Malaria currently ranks among the most prevalent infections in tropical and sub-tropical areas throughout the world with relatively high morbidity and mortality particularly in young children. The widespread occurrence and the increased incidence of malaria in many countries, caused by drug-resistant parasites (Plasmodium falciparum and P. vivax) and insecticide-resistant vectors (Anopheles mosquitoes), indicate the need to develop new methods of controlling this disease. Experimental vaccination with radiation-attenuated sporozoites can protect animals and humans against the disease, demonstrating the feasibility of developing an effective malaria vaccine. However, vaccines based on radiation-attenuated sporozoites are not feasible for large scale application due to lack of in vitro culture system. Therefore, the development of peptide-based subunit vaccines has been undertaken as an alternative approach. Synthetic peptides containing defined B- and T-cell epitopes of different antigens expressed in sporozoites and/or liver stages have been used as subunit vaccines in experimental animal models. They have been shown to be highly immunogenic and capable of inducing protective immunity mediated by antibodies, as well as CD4+ and CD8+ T-cells.     

Failure of Mycoplasma pneumoniae infection to confer protection against Mycoplasma genitalium: observations from a mouse model

Mycoplasma pneumoniae and M. genitalium are genomically distinct but share antigens that induce some serological cross-reactivity. Therefore, the possibility that M. pneumoniae infection of the human respiratory tract might provide immunity to M. genitalium infection of the genital tract was considered. Because of the difficulty of assessing this proposition in man, it was evaluated experimentally in a mouse model. Female BALB/c mice were susceptible to infection of the vagina with M. pneumoniae, whereas those infected previously in the oropharynx with M. pneumoniae were completely immune to infection of the vagina with this mycoplasma. However, all mice with such a respiratory tract infection were susceptible to infection of the vagina with M. genitalium. The findings suggest that an M. pneumoniae infection of the human respiratory tract is unlikely to influence infection of the genital tract by M. genitalium.     

Immune responses to mosquito saliva in 14 individuals with acute systemic allergic reactions to mosquito bites

BACKGROUND: Mosquito bite-induced acute systemic allergic reactions are an increasing clinical concern and have not been optimally characterized immunologically. OBJECTIVE: We wanted to study the immunologic basis of these reactions. METHODS: Sera were received from 14 individuals with a history of acute systemic allergic reactions to mosquito bites, defined as the presence of one or more of the following: urticaria, angioedema, wheezing, dyspnea, hypotension, and decrease or loss of consciousness. Ten individuals were from the United States and one each was from Canada, Germany, Japan, and Switzerland. An indirect ELISA was developed to measure specific IgE and IgG antibodies to saliva from 5 common mosquito species with different geographic distributions: Aedes aegypti, Aedes vexans, Aedes albopictus, Anopheles sinensis, and Culex quinquefasciatus. Twenty-nine individuals with negative bite test results from laboratory-reared mosquitoes served as control subjects. RESULTS: Mosquito saliva-specific IgE levels to all 5 species were significantly increased in the individuals with systemic allergic reactions compared with the control subjects ( P < .061 for Aedes vexans and P < .008 for the remaining 4 species). By using the mean of the control subjects plus 1 SD as a cut-off level, 11 individuals had positive results to Aedes albopictus and up to 4 additional species; 3 individuals had positive results to only one species. Saliva-specific IgG levels were not significantly increased in the individuals with systemic allergic reactions compared with levels seen in the control subjects ( P > .05). CONCLUSION: Acute systemic allergic reactions to mosquito bites involve mosquito saliva-specific IgE and can be characterized immunologically. Aedes albopictus is the most common species associated with systemic allergic reactions to mosquito bites.     

Generation of human monoclonal antibodies that confer protection against pertussis toxin.

A panel of human monoclonal antibodies reactive with pertussis toxin has been generated by means of Epstein-Barr virus infection. One of these, the 3F11 monoclonal antibody, showed the ability to neutralize in vitro and in vivo the toxic effects of the toxin. Western blot (immunoblot) analysis located the 3F11 epitope on the S3 subunit.