Seasonal dynamics of ammonia-oxidizing bacteria but not archaea influence soil nitrogen cycling in a semi-arid agricultural soil.

Nitrification, a key pathway of nitrogen (N) loss from agricultural soils, is performed by ammonia-oxidizing bacteria (AOB) and archaea (AOA). We examined the seasonal dynamics (2 years) of ammonia oxidizer gene abundances across a gradient of soil carbon (C) and N in a semi-arid soil after 8 years of tillage and crop residue treatments. AOB was more dominant than AOA in the surface soil, as AOA were undetected in 96% of samples. Seasonal variation in AOB abundance was related to substrate availability; AOB gene copy numbers increased at the end of the growing season (during summer fallow) following higher concentrations in dissolved organic matter soil water. This suggests increased co-location between AOB and substrate resources in pores still filled with water as the soils dried. AOB was however not statistically related to soil ammonium concentrations, soil water content, rainfall or temperature. Organic matter inputs enhanced AOB abundance independent of seasonal variation. AOB abundance was greatest in autumn and immediately preceding the start of the growing season, and coincided with elevated soil nitrate concentrations. The growth of the AOB population is likely to contribute to increased risk of N loss through leaching and/or denitrification at the start of the crop growing season following summer fallow.

Survival to patency of low level infections with Trichuris muris in mice concurrently infected with Nematospiroides dubius.

Large, single-pulse laboratory infections with Trichuris muris are rejected by mice before patency, but low-level infections of fewer than 20 worms survive for long periods. Data are presented to show that the threshold at which an effective immune response takes place is significantly higher in mice concurrently infected with Nematospiroides dubius. In control CFLP mice trickle infections did not survive to maturity but in the slower responder C57 Bl10 mice egg production began on Day 35 and continued for a further seven weeks, with some mature worms present at autopsy. Concurrent infection with N. dubius resulted in trickle infections, T. muris surviving much better than in control mice, although these still showed some resistance to T. muris. It is suggested that the results support the hypothesis that T. muris elicits concomitant immunity in the host. Thus, the first worms to establish survive to patency at which time they can no longer be removed by the host, but once the immunological threshold has been exceeded incoming larvae are rejected by the host. Such a survival strategy would be very useful to T. muris in the wild.

Functional antigens of Trichuris muris released during in vitro maintenance: their immunogenicity and partial purification.

The immunogenicity of the secretory exo-antigen (EXA) originating in the stichosome of Trichuris muris has been investigated. High levels of immunity to challenge were produced using EXA (100 micrograms) by subcutaneous administration. Vaccination with a range of doses of EXA in Freunds' Incomplete Adjuvant (FIA) showed a dose response; 1 microgram of EXA reduced the worm burden by 50% and doses of 10 micrograms or more reduced the worm burden by 80-90% at Day 9 post-infection. Worms recovered from vaccinated mice were significantly smaller than those from controls. A precipitin line identifiable with EXA was shown to immunize mice against T. muris challenge by vaccination. The protective antigen contained in EXA has been partially isolated using gel filtration, ion exchange filtration and isoelectric focusing and has been shown to be a protein of 30000 molecular weight having a pI of 6.8-7.3.

The activity of an anti-allergic compound, proxicromil, on models of immunity and inflammation.

A tricyclic chromone, proxicromil (sodium 6,7,8,9-tetrahydro-5-hydroxy-4-oxo-10-propyl-naphtho (2,3-b) pyran-2-carboxylate), has been tested for activity against certain immunological and inflammatory reactions. When given parenterally it suppressed the development of delayed hypersensitivity reactions in sensitized mice and guinea-pigs but did not affect the rejection of skin allografts in mice. The compound had no activity against certain in vitro correlates of delayed hypersensitivity reactions (lymphocyte transformation and lymphokine activity), but did have an inhibitory effect on lymphokine (MIF) productions at 10(-4) M but not at 10(-5) M. Proxicromil was also found to be active in non-immunologically mediated models of inflammation and in models having an immunological component which are known to be sensitive to non-steroidal anti-inflammatory drugs (adjuvant arthritis, reversed passive Arthus reaction). The activity of this compound was enhanced when administered in arachis oil when compared to its activity in saline. Proxicromil has not direct activity on the development of immune responsiveness but appear to suppress the expression of delayed hypersensitivity and immune complex mediated hypersensitivity reactions by virtue and its anti-inflammatory properties. This activity is not associated with inhibition of cyclo-oxygenase.

Oxygen-binding and immunological properties of complexes between dextran and animal haemoglobins.

Complexes of dextran 20 000 with haemoglobins of sheep, rabbit, dog, bovine and human origin were prepared through alkylation of haemoglobin by N-bromoacetylaminoethylamino-dextran. The yields were uniformly high. Complex-formation in each case was accompanied by the disappearance of reactive thiol groups on the haemoglobin, and by an increase in the affinity of the haemoglobin for oxygen. The immunological properties of dog, rabbit and sheep dextran-haemoglobin were investigated in both homologous and heterologous species. The complexes were found to be non-immunogenic in the homologous species. In heterologous species the anti-haemoglobin response induced by each complex was generally of a similar level to that induced by the haemoglobin alone.

Impairment of primary expulsion of Trichuris muris in mice concurrently infected with Nematospiroides dubius.

Primary immune expulsion of Trichuris muris was markedly delayed by concurrent infection with Nematospiroides dubius. Maximum delay of expulsion was dependent on size and timing of N. dubius infection relative to T. muris infection. In NIH mice infection with 400 N. dubius larvae immediately before or after T. muris infection was found to be most effective in suppressing expulsion. Infection on day 8 of T. muris infection, when mice are sensitized to T. muris, also impaired expulsion. From this evidence it is suggested that the larvae of N. dubius are immunosuppressive and that the efferent role of the immune response to T. muris is inhibited. The results are discussed in terms of non-specific immunosuppression and their relevance to the tropical disease situation is emphasized.