Identification of a surface antigen on Loa loa microfilariae the recognition of which correlates with the amicrofilaremic state in man

Filarial infections induce a spectrum of disease in their natural hosts, and by correlating immunity found in individuals with their disease pattern, one may delineate non-pathogenic, protective mechanisms. Loa loa is causal of mild to moderate pathology, and it is unique among the human filaria in that adult worms are occasionally visible during subconjunctival migration. To study immune mechanisms controlling microfilaremia, sera from 15 subjects with amicrofilaremic occult loiasis (OL) were compared with sera from 10 subjects with microfilaremic loiasis (ML) microfilaremia, (greater than 4000/ml) for their reactions with living microfilariae (mf). An IFA was first used to detect antibodies able to bind to the surface of living L. loa mf. ML subjects either did not react (7/10) or reacted only very weakly (3/10). Highly reactive sera were found only in OL subjects; 7/15 gave very bright fluorescence, 5/15 gave moderate reactions, and 3/15 were negative. Most of these antibodies were of the IgG class. Sera from all subjects were also reacted with living mf in an antibody-dependent cellular adherence test using normal leukocytes. Sera that were strongly positive in IFA showed strong adherence and IFA-negative sera were non-reactive. To identify the Ag involved, mf were surface iodinated, detergent-extracted Ag were immunoprecipitated, and Mr was determined on SDS-PAGE. Several OL sera, all highly reactive in the above tests, precipitated a 23-kDa molecule with which all ML sea failed to react. Sera from a mandrill experimentally infected with L. loa also precipitated the 23-kDa Ag when taken post-patency. In conclusion, it appears that certain people who control L. loa microfilaremia have high levels of IgG antibodies that bind to a surface Ag of 23 kDa and are able to mediate cellular adherence.     

Mechanisms of self-cure from Trypanosoma congolense infection in mice

The mechanism(s) of resistance to African trypanosomiasis caused by Trypanosoma congolense was investigated by using the Dinderesso/80/CRTA/3 isolate to which C57B1/6 are resistant (low parasitemia and self-cure) and BALB/c sensitive (high parasitemia and death). The resistance of C57B1/6 is similar to that found in some natural hosts of African trypanosomes such as certain indigenous West African cattle and wild Bovidae. The antibody response to epitopes exposed on the variant surface glycoprotein of a clone obtained from the Dinderesso/80/CRTA/3 isolate was measured by a complement-mediated lysis assay in C57B1/6 and BALB/c. After infections with 10(4), 10(5), or 10(7) motile organisms, antibody appeared in C57B1/6 4 to 8 days earlier than in BALB/c. Peak antibody titers were similar in both strains but were reached about 4 days earlier in C57B1/6. In this strain, antibody appeared during and controlled the first wave of parasitemia, whereas in BALB/c, parasitemia reached a plateau above 10(8) organisms per ml before antibody could be detected, and at this time the animals were dying. At peak antibody response, the proportion of immunoglobulin (Ig) M and IgG antibody was the same in both strains. The antibody response had the same kinetics in C57B1/6 and BALB/c after injection of 10(4), 10(5), and 10(7) lethally irradiated but intact parasites, but the peak titers were 10(3) to 10(4) times lower than after live challenge. The response to nonirradiated trypanosomes appeared to be T cell independent, because the antibody titers were the same in congenitally athymic nu/nu and normal C57B1/6, and no evidence for the induction of T cell activity could be demonstrated in the infected nude mice. A role for trypanolytic serum factors in resistance could not be demonstrated. The extent of immunosuppression after infection with nonirradiated organisms was compared in the two strains by measuring the in vitro response of their splenic lymphocytes to concanavalin A, pokeweed mitogen, and allogeneic cells and their ability to mount an in vivo response to an unrelated trypanosome challenge. Both strains were partially immunosuppressed during rising parasitemia, but as C57B1/6 controlled parasitemia, immunosuppression was gradually reversed, whereas in BALB/c it became worse. Several explanations might account for the resistance of C57B1/6 to the Dinderesso/80/CRTA/3 isolate of T. congolense. It appears that an early immune response is a decisive factor in this resistance.     

Trypanosoma brucei: analysis of relapsing populations in sensitive and resistant breeds of cattle

The clone DiTat 1.1 of Trypanosoma brucei brucei was injected into four bovids, and clones obtained from successive waves of parasitemia were used to study the expressed variant-specific surface glycoprotein repertoire. Twenty-four clones were obtained which could be classified into 12 different variable antigen types, in addition to the clone injected, using agglutination or immunofluorescence with monospecific antisera. The variable surface glycoproteins of the 25 clones were extracted using the detergent octyl-beta-D-glucopyranoside in the presence of the protease inhibitor, N-cbz-L-phenylalaninechloromethylketone. The molecular weights varied from 52,000 to 69,000 and the pI from 5.0 to 8.8. The virulence of 14 clones representing 13 variable antigen types was ascertained in mice. The mean survival time ranged from 20.5 to 43.0 days. Clones isolated from early peaks of parasitemia in the bovid were the most virulent while clones derived from later peaks were less virulent. It seems that organisms of diminishing virulence appear in bovids, leading to self-cure of the disease. All clones were sensitive to human serum in a blood infectivity inhibition test. Antibody against all virulent clones appeared in 20 cattle (10 Zebus, 10 Baoulés) which had been injected with T. brucei DiTat 1.1. There was no evidence for parasites of high or low virulence being preferentially expressed in resistant or sensitive hosts.     

Comparison of the cellular internalization of antibodies used either as immunotoxins or in ADEPT

The internalization into tumor cells of two antibodies (C242 and 454A12), which make potent immunotoxins when linked to ricin A-chain, and an antibody (A5B7), which does not make a potent immunotoxin but has proven useful in ADEPT, was evaluated. The 454A12 antibody was rapidly taken into the cells, 50% of the antibody being internalized after 2 h. The C242 antibody was internalized more slowly, approx 50% being taken up by the cells in 24 h. With A5B7, less than 10% of the antibody was internalized after 24 h. Internalization of the C242 antibody was accompanied by the appearance of antibody degradation products in the cell medium after 2 h, and this degradation could be inhibited by addition of a metabolic inhibitor that prevented cell internalization. In contrast, minimal degradation of the A5B7 antibody could be detected up to 24 h after binding to the cells. In conclusion, both 454A12 and C242 antibodies, which make potent immunotoxins, were internalized into tumor cels. The A5B7 antibody, which does not make a potent immunotoxin, was not internalized, and this property may be one reason why A5B7 has proved useful for delivery of enzymes in ADEPT.     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

The pathway of biosynthesis of nicotinamide–adenine dinucleotide in rat mammary gland

1. The pathway of NAD synthesis in mammary gland was examined by measuring the activities of some of the key enzymes in each of the tryptophan, nicotinic acid and nicotinamide pathways. 2. In the tryptophan pathway, 3-hydroxyanthranilate oxidase and quinolinate transphosphoribosylase activities were investigated. Neither of these enzymes was found in mammary gland. 3. In the nicotinic acid pathway, nicotinate mononucleotide pyrophosphorylase, NAD synthetase, nicotinamide deamidase and NMN deamidase were investigated. Both NAD synthetase and nicotinate mononucleotide pyrophosphorylase were present but were very inactive. Nicotinamide deamidase, if present, had a very low activity and NMN deamidase was absent. 4. In the nicotinamide pathway both enzymes, NMN pyrophosphorylase and NMN adenylyltransferase, were present and showed very high activity. The activity of the pyrophosphorylase in mammary gland is by far the highest yet found in any tissue. 5. The apparent K(m) values for the substrates of these enzymes in mammary gland were determined. 6. On the basis of these investigations it is proposed that the main, and probably only, pathway of synthesis of NAD in mammary tissue is from nicotinamide via NMN.     

Biodiversity of 52 chicken populations assessed by microsatellite typing of DNA pools

In a project on the biodiversity of chickens funded by the European Commission (EC), eight laboratories collaborated to assess the genetic variation within and between 52 populations from a wide range of chicken types. Twenty-two di-nucleotide microsatellite markers were used to genotype DNA pools of 50 birds from each population. The polymorphism measures for the average, the least polymorphic population (inbred C line) and the most polymorphic population (Gallus gallus spadiceus) were, respectively, as follows: number of alleles per locus, per population: 3.5, 1.3 and 5.2; average gene diversity across markers: 0.47, 0.05 and 0.64; and proportion of polymorphic markers: 0.91, 0.25 and 1.0. These were in good agreement with the breeding history of the populations. For instance, unselected populations were found to be more polymorphic than selected breeds such as layers. Thus DNA pools are effective in the preliminary assessment of genetic variation of populations and markers. Mean genetic distance indicates the extent to which a given population shares its genetic diversity with that of the whole tested gene pool and is a useful criterion for conservation of diversity. The distribution of population-specific (private) alleles and the amount of genetic variation shared among populations supports the hypothesis that the red jungle fowl is the main progenitor of the domesticated chicken.