Immunization of mice against Naegleria fowleri infection

Structural informatics approach for designing an epitope-based vaccine against the brain-eating Naegleria fowleri

Primary Amoebic Meningoencephalitis (PAM), a severe lethal brain disease, is caused by a parasite, Naegleria fowleri, also known as the "brain-eating amoeba". The chances of a patient's recovery after being affected by this parasite are very low. Only 5% of people are known to survive this life-threatening infection. Despite the fact that N. fowleri causes a severe, fatal infection, there is no proper treatment available to prevent or cure it. In this context, it is necessary to formulate a potential vaccine that could be able to combat N. fowleri infection. The current study aimed at developing a multi-epitope subunit vaccine against N. fowleri by utilizing immunoinformatics techniques and reverse vaccinology approaches. The T- and B-cell epitopes were predicted by various tools. In order to choose epitopes with the ability to trigger both T- and B-cell-mediated immune responses, the epitopes were put through a screening pipeline including toxicity, antigenicity, cytokine-inductivity, and allergenicity analysis. Three vaccine constructs were designed from the generated epitopes linked with linkers and adjuvants. The modeled vaccines were docked with the immune receptors, where vaccine-1 showed the highest binding affinity. Binding affinity and stability of the docked complex were confirmed through normal mode analysis and molecular dynamic simulations. Immune simulations developed the immune profile, and in silico cloning affirmed the expression probability of the vaccine construct in Escherichia coli (E. coli) strain K12. This study demonstrates an innovative preventative strategy for the brain-eating amoeba by developing a potential vaccine through immunoinformatics and reverse vaccinology approaches. This study has great preventive potential for Primary Amoebic Meningoencephalitis, and further research is required to assess the efficacy of the designed vaccine.

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Synergistic activities of azithromycin and amphotericin B against Naegleria fowleri in vitro and in a mouse model of primary amebic meningoencephalitis

Naegleria fowleri is responsible for producing a rapidly fatal central nervous system infection known as primary amebic meningoencephalitis (PAM). To date, amphotericin B, an antifungal agent, is the only agent with established clinical efficacy in the treatment of PAM. However, amphotericin B is not always successful in treating PAM and is associated with severe adverse effects. We previously found azithromycin to be more effective than amphotericin B in a mouse model of PAM. We therefore investigated the combination of amphotericin B and azithromycin in vitro and in a mouse model of PAM. For the in vitro studies, 50% inhibitory concentrations were calculated for each drug alone and for the drugs in fixed combination ratios of 1:1, 3:1, and 1:3. We found amphotericin B and azithromycin to be synergistic at all three of the fixed combination ratios. In our mouse model of PAM, a combination of amphotericin B (2.5 mg/kg of body weight) and azithromycin (25 mg/kg) protected 100% of the mice, whereas amphotericin B alone (2.5 mg/kg) protected only 27% of mice and azithromycin alone (25 mg/kg) protected 40% of mice. This study indicates that amphotericin B and azithromycin are synergistic against the Lee strain of N. fowleri, suggesting that the combined use of these agents may be beneficial in treating PAM.

Free-living amoebae: pathogenicity and immunity

Free-living amoebae causes three well-defined disease entities: (i) primary amoebic meningoencephalitis, caused by Naegleria fowleri, (ii) granulomatous amoebic encephalitis and (iii) chronic amoebic keratitis, caused by species of Acanthamoeba. Both Naegleria infections and chronic amoebic keratitis occur in healthy individuals while granulomatous amoebic encephalitis is often associated with patients with acquired immunodeficiencies. The different pathogenic behaviour of these organisms is associated with differences in life cycle, amoeboidal locomotion, enzyme composition (such as phospholipase A), and cytotoxins, as well as natural host immunity. Immunity against these amoebae (whether acquired or natural) involves a combination of complement, antibody and cell-mediated immunity. Evidence suggests that the major mechanisms of immunity against these amoebae is activation of phagocytic cells, especially neutrophils, by lymphokines and opsonization of the amoebae by antibody which promote an antibody dependent cellular destruction of the organism.

Altered neutrophils in mice immune to experimental Naegleria amoebic meningoencephalitis

Naegleria fowleri is the cause of primary amoebic meningoencephalitis in man. The mouse is considered to be a suitable experimental model for this disease. The data presented shows that blood neutrophils from N. fowleri immune mice (immunised) that had received a 'recall' amoeba antigen had altered responses compared with those from similarly treated normal mice. The neutrophils from immune animals showed increased basal levels of oxygen-dependent respiratory activity, measured by the chemiluminescence response. These neutrophils also showed increased responses to formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), phorbol myristate acetate (PMA), and opsonized N. fowleri. The results are consistent with previous data suggesting that the neutrophil (and its activation) is important in defence against N. fowleri.

[Studies on the cell-mediated immunity in experimental Naegleria spp. infections]

Observations were made on the differences in cell-mediated immune responses in the mice infected with strongly pathogenic Naegleria fowleri ITMAP 359, weakly pathogenic Naegleria jadini 0400, or non-pathogenic Naegleria gruberi EGB, respectively. Variations in cell-mediated responses and changes in antibody titers according to the duration after infection were noted. Infections were done by dropping 5 microliters saline suspension containing 10 x 10(4) trophozoites cultured axenically in the CGVS medium into the right nasal cavity of ICR mice aging about 6-7 weeks, under the anesthesia by intraperitoneal injection of secobarbital. Following infection, delayed type hypersensitivity(DTH) responses in the footpad and blastogenic responses of the mouse spleen cells using [3H]-thymidine were observed on the day 1, 4, 7, 10 and 14 after infection. For the preparation of amoeba lysates, each of cultured trophozoites were homogenized with an ultrasonicator, and centrifugated at 20,000 g. The supernatants of amoeba lysates were used as the mitogen and antigen for ELISA. Concanavalin A(Con. A) and lipopolysaccharide(LPS) were also used as mitogens in the blastogenic response. 1. The mice infected with N. fowleri showed the mortality rate of 75.7%. The rate was 6.2% for the N. jadini infected group, while no dead mouse was observed for N. gruberi infections. 2. In regard to DTH responses in the N. fowleri infected mice, the level increased in comparison to the control group but declined after 7 days. An increase was also noted for the N. jadini group after 1 day, but gradual decreases were observed through the infection period. In addition, no difference was noted between the N. gruberi infected and control groups. 3. Concerning the blastogenic response of the splenocytes, it increased after 10 days in the experimental group of N. fowleri infection, but the differences were not statistically significant compared with control group. It was evident that N. jadini group was not different from control group either, while there was a tendency of decrease in N. gruberi infected group. In regard to the blastogenic response of the splenocytes by LPS, it was found that the N. fowleri, N. jadini and N. gruberi infected groups had no differences from the control group. 4. The serum antibody titer of N. fowleri and N. jadini infected mice increased from the day 7 and 14 after infection respectively, while the N. gruberi infected mice showed no increase.(ABSTRACT TRUNCATED AT 400 WORDS)

Depression of immunity to Naegleria fowleri in mice by selective depletion of neutrophils with a monoclonal antibody

In an attempt to define the role of neutrophils in immunity to Naegleria fowleri in vivo, we examined the effects of treating immunized (with amoeba culture supernatant antigen) mice with the monoclonal antibody NIMP-R10, which binds to neutrophil complement receptor type 3bi (CR3) and causes selective neutrophil depletion in mice. Mice in the nonimmunized group challenged with amoebae all died by day 12, while 97% in the immunized group survived. By contrast, the immunized group treated with NIMP-R10 showed only 25% survival. The immunized group treated with "control" mouse ascites, WEM-G11, was highly resistant (90% survival). There was a significant neutrophil response in the nasal mucosa and olfactory lobes of immunized, NIMP-R10-treated mice, despite a marked degree of neutropenia similar to that seen in immunized, untreated mice. Nonimmunized mice showed virtually no neutrophil response. Despite this response in the NIMP-R10-treated mice, amoebic proliferation was not depressed, and there was no evidence of neutrophil degranulation or amoebic killing, despite the close apposition of large numbers of neutrophils to amoebae. The results indicate that neutrophils are necessary for the expression of immunity to N. fowleri.

The role of antibody in immunity against experimental naegleria meningoencephalitis ('amoebic meningitis')

Mice immunized with amoeba culture fluid (ACF) from axenically cultured Naegleria fowleri showed marked protection against a lethal amoeba challenge, a result consistent with previous observations from this laboratory. The nature of this acquired resistance is not known. The data presented show that the degree of protection conferred to mice by immunization is related to the levels of antinaegleria antibodies. These antibodies react with the surface of the amoeba. The data also show that serum (and the IgG serum fraction) from immunized mice confer protection to normal mice against a lethal N. fowleri challenge. Spleen cells from immunized animals were only capable of conferring protection to recipients, when the challenge time was delayed (10 days), at which time anti-naegleria antibodies appeared in the serum of the mice. The studies suggest that antibodies play an important role in the ACF-induced resistance to experimental naegleria meningoencephalitis.

Intranasal immunization of mice against Naegleria fowleri

The purpose of this research was to determine whether mice could be protected from lethal challenge with Naegleria fowleri by prior intranasal exposure to pathogenic and nonpathogenic Naegleria. Mortality ranged from 0 to 100% for mice inoculated intranasally (i.n.) with 5 x 10(3) amebae of 13 human isolates of N. fowleri. Mice were immunized and challenged i.n. using live amebae of strains of low, medium, and high virulence. The greatest protection against lethal challenge was afforded by three immunizing doses of 10(3) amebae per dose of the strain of medium virulence. Nonpathogenic N. gruberi also was used to immunize mice i.n. against lethal challenge with N. fowleri. Protection was greater following immunization with N. gruberi than it was after immunization with N. fowleri, suggesting that nonpathogenic N. gruberi may be a better immunogen in protecting mice against lethal naeglerial challenge.

Serology of Naegleria fowleri and Naegleria lovaniensis in a hospital survey

An avidin-biotin horseradish peroxidase method was used to detect antibodies to Naegleria fowleri and N. lovaniensis in human serum samples. Antibodies were detected in 101 specimens from 115 hospital patients ranging in age from 15 to 98 years. Class-specific anti-immunoglobulins identified antibodies as IgG and IgM. IgG antibody titers to both species ranged from 1:20 to 1:640. Seven of 15 serum samples collected from newborn infants also demonstrated IgG antibodies to these organisms with a titer range of 1:20 to 1:80. The immunoperoxidase test and Western blot analysis of selected serum samples demonstrated a close similarity in serological results between N. fowleri and N. lovaniensis.

Efficacy of immune therapy in early experimental Naegleria fowleri meningitis

Naegleria fowleri meningoencephalitis is usually fatal in humans despite treatment. As a new approach, we tested intracisternal passive immune therapy in rabbits with amebic meningoencephalitis by using antinaegleria immune serum, an immunoglobulin G fraction, and a newly developed monoclonal antibody to N. fowleri. Both the immune serum and an immunoglobulin G fraction isolated from it by affinity chromatography provided a consistent, although temporary, protective effect, shown by prolongation of survival (P = 0.001). Multiple doses of immune serum further prolonged survival (P = 0.005). The protective effect of serum was retained after heating to 56 degrees C. We then developed a monoclonal antibody to N. fowleri which provided similar protection. Passive intracisternal antibody therapy might serve as an adjunctive component in the treatment of amebic meningoencephalitis.

Curative properties of muramyl dipeptide in experimental Naegleria meningoencephalitis

Naegleria fowleri is a free-living amoeba which causes a fatal meningoencephalitis in man. Mice injected with the immunostimulant MDP or an attenuated 11RX strain of Salmonella enteritidis showed some resistance to an intranasal challenge with N. fowleri. In addition it was observed that some of the mice infected with N. fowleri and showing symptoms of naegleria meningoencephalitis, given a single injection of MDP were cured of this disease. Our findings suggest that the use of immunostimulants could be a new approach in the quest for therapeutic agents for this disease.

[Protective immunity against Naegleria meningoencephalitis in mice]

This study is to verify the protective ability against experimental Naegleria meningoencephalitis by immunization with Naegleria fowleri in mice. Naegleria fowleri, strain 0359, and Naegleria gruberi, strain EGB, were used in this study, and cultured in CGVS medium axenically. Inbred BALB/c mice, weighing about 20g, were immunized by three intraperitoneal injection of 1 x 10(6) N. fowleri trophozoites at the interval of one week. This N. fowleri trophozoites antigen was fixed with 5 percent formaldehyde. N. fowleri trophozoites from culture were homogenized with sonicator at 4 degrees C as monitored by phase contrast microscopy, and their membrane and cell content preparations were made for the immunization of mice. Their inoculation dose in volume was equivalent to the 1 x 10(6) trophozoites in each injection for immunization. And N. gruberi trophozoites, which was fixed with 5 percent formaldehyde, were also used for immunization. Mice were inoculated intranasally with 5 x 10(4) N. fowleri trophozoites in a 5 microliter suspension under anesthesia by as intraperitoneal injection of about l mg secobarbiturate. Nervousness, rotation or sluggish behaviour were observed in the mice which were infected with N. fowleri. Necrotic lesion was demonstrated in the anterior portion of brain, especially in the olfactory lobe. The inflammatory cell infiltration with numerous N. fowleri trophozoites was noticed. This pathological changes were more extensive in the control than in the experimental groups. Mice were dead due to experimental primary amoebic meningoencephalitis that developed between 8 days and 23 days after inoculation. Mortality rate of the mice was low in the immunized experimental group. Mean survival time, which is the survival duration of mice from the infection to death, was prolonged significantly in the immunized mice except in the mice immunized with N. fowleri membrane. Even in the mice immunized with N. gruberi, survival time was delayed. In summary, the effectiveness of immunization is demonstrated in terms of protective immunity against Naegleria meningoencephalitis in mice.

Mitogenicity of Naegleria fowleri extract for murine T lymphocytes

The whole-killed pathogenic free-living amoeba, Naegleria fowleri, contained mitogenic activity (NFM) for mouse spleen cells. Similar preparations from the non-pathogenic amoeba N. gruberi and the pathogenic Acanthamoeba culbertsoni lacked mitogenic activity. Fluids from N. fowleri cultures, containing amoeba antigens, also failed to cause proliferation of mouse spleen lymphocytes. Spleen cells from athymic nude mice failed to respond to NFM. In addition, nylon wool non-adherent, but not the adherent, spleen cell subpopulation proliferated in the presence of NFM. These results show that the factor(s) is mitogenic for T lymphocytes. The spleen cells from mice treated with cyclophosphamide doses known to deplete T suppressor cell activity from this organ failed to respond to NFM, indicating that NFM may be mitogenic for T suppressor cells.

Immunization with killed Acanthamoeba culbertsoni antigen and amoeba culture supernatant antigen in experimental Acanthamoeba meningoencephalitis

Mice immunized with killed (sonicated) Acanthamoeba culbertsoni A-1 antigen displayed marked resistance to intranasal challenge with the amoeba. A primary immunization produced a survival rate of approximately 40%, and survival values of greater than 80% were obtained by multiple immunizations. Similarly mice immunized with fluids from A-1 cultures were highly resistant to infection.

Host resistance of mice to Naegleria fowleri infections

Naegleria fowleri is an etiological agent of primary amoebic meningoencephalitis in humans and laboratory animals. The determinative factors in host resistance of mice to N. fowleri infections have not been fully characterized. Male or female B6C3F1 mice stimulated by intraperitoneal administration of 10(6) amoebae of N. fowleri nN68 per mouse produced agglutinating activity and markedly elevated levels of serum and immunoglobulins M and G. Despite a marked humoral response, protective immunity was increased only marginally by active immunization. Host resistance was not impaired by prior treatment with 350 rads of 60Co radiation or 200 mg of cyclophosphamide per kg or by concurrent daily treatment with 30 mg of cyclophosphamide per kg for 14 days. Moreover, host resistance was not impaired by daily treatment with 4 mg of diethylstilbestrol per kg for 14 days, with challenge on day 2 of drug exposure or 24 h after the last drug treatment. Mice depleted of hemolytic complement by cobra venom factor were more susceptible to N. fowleri infection than were untreated mice.

Site of expression of immunity to Naegleria fowleri in immunized mice

An experiment was performed which confirmed a previous finding that mice are protected against Naegleria fowleri infection by immunization with amoeba-free supernatant from amoeba cultures. Histological observations suggested that this protection is expressed mainly at the nasal mucosa and possibly results from the combined effects of polymorphonuclear leucocyte-mediated killing of the amoeba and mechanical elimination of the organisms by extensive shedding of necrotic epithelium.

Cell-mediated killing of protozoa

Cell-mediated immunity represents an important host defence mechanism against protozoal infections. The effector cells directly involved are neutrophils, macrophages and, ultimately, activated macrophages. Within this simple scheme there are, however, considerable variations in activity. Effector cells from different animal species, and even from different strains of the same species, may be more or less effective in controlling a certain protozoal infection. Different protozoa differ in their susceptibility to cell-mediated killing according to genus, species, strain and morphological form. The most susceptible morphological form is that which occurs in the insect vector, and which has not yet adapted to protect itself from the vertebrate host. Epimastigotes of Trypanosoma and promastigotes of Leishmania are readily killed by phagocytic cells, while the corresponding trypomastigote and amastigote forms are considerably more resistant. Protozoa which live in macrophages, such as amastigotes of Leishmania, endozoites (tachyzoites) of Toxoplasma and amastigotes of reticulotropic strains of T. cruzi, have developed a remarkable resistance to the microbicidal activity of the host cell. Conversely, amastigotes of myotropic strains of T. cruzi, which live in muscle cells, have not developed this resistance to cell-mediated killing by macrophages. Readily accessible protozoa, such as T. brucei trypomastigotes and Plasmodium merozoites in the bloodstream, while they lack the marked resistance developed by reticulotropic protozoa, have a partial protection since they are attacked by phagocytic cells only when specific antibody is present. Granulocyte-mediated killing can be largely attributed to neutrophils. Eosinophils appear to play only a minor role and compete ineffectually when neutrophils are also present. The only group of protozoal species which may be significantly controlled by eosinophils are the stercorarian species of Trypanosoma. In vitro experiments show that antibody-coated trypomastigotes of T. cruzi can be killed by eosinophils, although there is little evidence that this occurs in vivo. Interestingly, this is the only species that has been reported to be susceptible to the major basic protein of eosinophils, a toxic component of the lysosomal granules which is very active against helminths. Neutrophils are not very active against endozoites of Toxoplasma gondii, Trypanosoma, trypomastigotes of salivarian Trypanosoma, free merozoites of Plasmodium, and promastigotes and amastigotes of Leishmania.(ABSTRACT TRUNCATED AT 400 WORDS)

Parasitic amebae in Korea

This review dealt with biology, host-parasite relationship, symptomatology, epidemiology, diagnosis, treatment of Entamoeba histolytica infection and free livng amoeba.

Immunity to pathogenic free-living amoebae: role of humoral antibody

Pathogenic free-living amoebae are common in nature, but few clinical infections by these amoebae have been reported. This has prompted studies of host susceptibility factors in humans. A survey of normal human sera from three New Zealand Health Districts was made; antibodies to pathogenic free-living amoebae were found in all sera, with titers ranging from 1:5 to 1:20 for Naegleria spp. and from 1:20 to 1:80 for Acanthamoeba spp. The antibodies belonged mainly to immunoglobulin G and immunoglobulin M classes. The presence of a specific neutralizing factor against Acanthamoeba spp. but not Naegleria spp. was demonstrated. Possible protective mechanisms are discussed.

Immunity to pathogenic free-living amoebae: role of cell-mediated immunity

The role of cell-mediated immunity in defense against pathogenic free-living amoebae was examined. Both the in vitro macrophage inhibition test and the in vivo delayed hypersensitivity test showed responses to both heterologous and homologous antigens, although homologous systems were the most efficient. It is suggested that exposure to nonpathogenic species of free-living amoebae can stimulate the immune system to be effective against pathogenic species. The significance of cell-mediated immunity as a defense against invasion by pathogenic free-living amoebae is discussed.

Immunization with culture supernatant in experimental amoebic meningoencephalitis

Mice were immunized with 0.25 ml culture supernatant intraperitoneally and challenged with 5 x 10(4) Naegleria fowleri intranasally. Survival rate was 11% after one and 25% after three immunizing doses, compared to 0% in controls.

Innate resistance of mice to experimental infection with Naegleria fowleri

The mouse system provides an excellent model for studying host resistance to Naegleria fowleri, the agent of primary amoebic meningoencephalitis. Innate resistance to infection with N. fowleri was examined with respect to infecting dose and the age, sex, and strain of mice. Intravenous inoculation with 10(7) amoebae per mouse produced 100% mortality in 9 days, whereas inoculation with fewer amoebae reduced the cumulative mortality. Male and female DUB/ICR mice of varying ages were inoculated intravenously with 2.5 X 10(5) N. fowleri per g of body weight. The youngest mice died first, with 100% mortality for both males and females, and mortality decreased with increasing age. Female mice were significantly more resistant to infection than males. Five strains of mice weighing approximately 20 g were inoculated intravenously with weight-adjusted doses; mortality ranged from 10% in C57BL/6 mice to 95% in A/HeCr mice.