A radioimmunoassay for human antibody specific for microbial antigens

Detection of serum antibodies in children and adolescents against Balamuthia mandrillaris, Naegleria fowleri and Acanthamoeba T4

The presence of free-living amoebae of the genera Naegleria, Acanthamoeba and Balamuthia, which contain pathogenic species for humans and animals, has been demonstrated several times and in different natural aquatic environments in the northwest of Mexico. With the aim of continuing the addition of knowledge about immunology of pathogenic free-living amoebae, 118 sera from children and adolescents, living in three villages, were studied. Humoral IgG response against B. mandrillaris, N. fowleri and Acanthamoeba sp. genotype T4, was analyzed in duplicate to titers 1: 100 and 1: 500 by enzyme-linked immunosorbent assay (ELISA). Children and adolescents ages ranged between 5 and 16 years old, with a mean of 9 years old, 55% males. All tested sera were positive for the 1: 100 dilution, and in the results obtained with the 1: 500 dilution, 116 of 118 (98.3%) were seropositive for N. fowleri, 101 of 118 (85.6%) were seropositive for Acanthamoeba sp. genotype T4, and 43 of 118 (36.4%) were seropositive for B. mandrillaris. The statistical analysis showed different distributions among the three communities and for the three species of pathogenic free-living amoebae, including age. Lysed and complete cells used as Balamuthia antigens gave differences in seropositivity.

Antagonistic action of the bacterium Bacillus licheniformis M-4 toward the amoeba Naegleria fowleri

Free-living amoebae belonging to the species Naegleria fowleri are known to be the etiological agents for a form of fulminant meningoencephalitis that is generally fatal (primary amoebic meningoencephalitis). In a broad bacterial screening from soil and water we have isolated three strains (M-4, D-13 and A-12) belonging to the species Bacillus licheniformis that have remarkable amoebicidal activity against Naegleria sp. and also against different Gram-positive and Gram-negative bacteria. Physical-chemical characteristics, partial purification and biological activities of a substance produced by the M-4 strain have been investigated. This substance (m-4) is stable at high temperature (up to 100 degrees C) and extremes of pH (2.5-9.5) and also at -20 degrees C for months. Its production is greatly influenced by oxygenation of the cultures and is probably related to the sporulation process of the bacterium. Scanning electron microscope observations reveal that amoebae are lysed after a few minutes contact with m-4.

Epidemiology of free-living ameba infections

Small free-living amebas belonging to the genera Acanthamoeba and Naegleria occur world-wide. They have been isolated from a variety of habitats including fresh water, thermal discharges of power plants, soil, sewage and also from the nose and throats of patients with respiratory illness as well as healthy persons. Although the true incidence of human infections with these amebas is not known, it is believed that as many as 200 cases of central nervous system infections due to these amebas have occurred worldwide. A majority (144) of these cases have been due to Naegleria fowleri which causes an acute, fulminating disease, primary amebic meningoencephalitis. The remaining 56 cases have been reported as due either to Acanthamoeba or some other free-living ameba which causes a subacute and/or chronic infection called granulomatous amebic encephalitis (GAE). Acanthamoeba, in addition to causing GAE, also causes nonfatal, but nevertheless painful, vision-threatening infections of the human cornea, Acanthamoeba keratitis. Infections due to Acanthamoeba have also been reported in a variety of animals. These observations, together with the fact that Acanthamoeba spp., Naegleria fowleri, and Hartmannella sp. can harbor pathogenic microorganisms such as Legionella and or mycobacteria indicate the public health importance of these amebas.

Biology of Naegleria spp

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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.

Specificity of antibodies from human sera for Naegleria species

Serum samples from adult humans in North Carolina and Pennsylvania were assayed for antibodies against four Naegleria species: N. australiensis, N. fowleri, N. gruberi, and N. lovaniensis. Agglutinating activities of serum samples from North Carolina subjects were higher for N. fowleri than were those from Pennsylvania subjects. The distributions of agglutination titers of human serum samples for N. australiensis, N. gruberi, and N. lovaniensis were heterogeneous. The agglutination capabilities of selected serum samples absorbed with rounded, killed trophozoites of N. australiensis and N. lovaniensis were distinctly different, as were those of serum samples absorbed with N. fowleri and N. gruberi. N. australiensis and N. gruberi shared some agglutinating antigens, as did N. fowleri and N. lovaniensis. The agglutinating activities of most serum samples correlated with the capability of their immunoglobulin M (IgM) to bind to antigens in extracts of Naegleria species but not with the capabilities of their IgG to bind to antigens of Naegleria species. Absorption of IgM binding capability with rounded, killed trophozoites established that N. gruberi was distinctly different from N. fowleri and N. lovaniensis but that N. fowleri and N. lovaniensis shared surface antigens. The proteins in extracts of the four Naegleria species were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and tested for their ability to bind immunoglobulins in a serum sample. The antigens of the four species that bound IgM or IgG in the tested serum sample were separated by SDS-PAGE, and when they were incubated with anti-IgM or anti-IgG, they gave distinct profiles. There was one distinct, shared antigen that had a molecular size of 40,000 daltons. Absorption of the test serum with killed, rounded trophozoites did not markedly change the immunoglobulin binding profile for Naegleria internal antigens separated by SDS-PAGE and did not remove the shared 40,000-dalton protein(s). These results demonstrate that the four Naegleria species have antigenically distinct surfaces and that humans have been individually exposed to antigens of Naegleria species.

Comparison of direct and indirect immunoradiometric assays (IRMA) for Bacillus anthracis spores immobilised on multispot microscope slides

A solid phase immunoradiometric assay (IRMA) is described in which Bacillus anthracis spores were heat fixed to the wells of glass multispot microscope slides. Assays for spores of B. anthracis Vollum and Sterne strains with 3H labels were evaluated in the direct and indirect versions. Neither single nor signal-to-noise characteristics of indirect assays were greatly improved by the use of immunopurified antibody (IPAB) or IgG anti-bacterial reagents rather than antiserum. However, the specificity of the direct and indirect assays for B. anthracis strains and B. cereus NCTC 8035 was altered by immunopurification of the anti-bacterial reagent. Although the signal-to-noise ratio was sometimes higher in indirect than in direct assays, signal values were usually no better. Evidence was produced that the overall ratio of the indirect : direct antibody molecules bound by preparations of B. anthracis spores rarely exceeded two but the antibody-molecular ratio for antigens on extracellular material in spore preparations was much higher than the ratio for antigens on the spores themselves.

Agglutination of Naegleria fowleri and Naegleria gruberi by antibodies in human serum

The capability of serum samples from 423 human subjects to agglutinate rounded cells of Naegleria fowleri nN68 was assessed. Sera from the umbilical cords of seven infants failed to agglutinate N. fowleri cells. The median agglutination titer was 1:4 for sera from children through age 4 years, 1:8 for sera from juveniles 5 to 15 years of age, and 1:16 for sera from subjects 15 to 30 years old. The agglutination titers of sera from older adults decreased to a median of 1:8 for the 40- to 60-year-old age group and to 1:4 for the 60- to 90-year-old subjects. Serum samples from young adults agglutinated rounded cells of both N. fowleri and N. gruberi. The agglutination activity for N. fowleri was removed by absorption with N. fowleri but not with N. gruberi. Conversely, agglutination activity for N. gruberi was removed by absorption with N. gruberi but not with N. fowleri. The agglutinating activity for N. fowleri was immunoglobulin M. Serum samples from children displayed markedly disparate capabilities to agglutinate N. fowleri and N. gruberi. Only rounded cells of N. fowleri or N. gruberi were reliably agglutinated by human serum samples. Live or paraformaldehyde-killed cells could be used in the assay, but live N. gruberi cells returned to the amoeboid form, and these agglutinated poorly.

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.

Radioimmunoassay of class-specific antibodies to Streptococcus mutans in monkey serum and saliva

A radioimmunoassay (RIA) has been developed to measure class-specific antibodies to Steptococcus mutans in the serum and saliva of monkeys (Macaca fascicularis). Anti-human immunoglobulin antibodies purified by affinity chromatography on immobilised monkey immunoglobulins and labelled with 125I were employed. Formolised cells of S. mutans and an extract of culture supernatant adsorbed to polystyrene wells were used as solid-phase antigens. The coefficients of variation for IgG, IgA and IgM assays were less than or equal to 10% for both antigen systems. Two monkeys were immunised with formolised cells of S. mutans by subcutaneous injection and subsequent instillation of bacterial cells into their right parotid ducts. IgG, IgA and IgM antibody responses to S. mutans in samples of serum and saliva were quantitated by RIA. Immobilisation of purified components of S. mutans on polystyrene wells enabled the measurement of antibody response to a number of antigens to be made. The RIA is a sensitive, reproducible and quantitative method of measuring serum and salivary antibody responses in monkeys.

A solid phase radiommunoassay on hydrophobic membrane filters: detection of antibodies to gonococcal surface antigens

A solid phase radioimmunoassay (SPRIA) has been developed for detection of IgG antibodies to gonococcal outer membrane components. Gonococcal antigens were immobilized on a solid support by covalent coupling to CNBr-activated Sepharose in the presence of the detergent Triton X-100. Binding of specific antibody to the Sepharose-antigen complex was detected using radiolabelled Protein A as the antiglobulin. Protein A was labelled by radioacetylation with tritiated acetic anhydride, yielding a product of high specific activity and high stability. No detectable loss of activity was observed over a ten month period. The entire assay was performed on Mitex teflon hydrophobic membrane filters which held the Sepharose beads and aqueous supernatant as a discrete drop of liquid. The supernatants and incubation media were easily and rapidly removed from the beads by suction on a specially designed manifold system. This procedure removed the need for repeated and time-consuming centrifugations. Titres were obtained graphically from double log plots of cpm bound versus antiserum dilution by extrapolation of the straight line to a point corresponding to twice the control level of radioactivity binding. The assay proved to be a very reliable and simple procedure for the detection of IgG antibodies to gonococcal surface antigens.