The identification of those components of Ascaris lumbricoides (var. suum) body fluid (ABF) which are IgE-inducing antigens (allergens) was found to depend on the type of assay used. By use of the radioallergosorbent test and sera from humans naturally infected with A. lumbricoides, it was found that ABF contains a range of allergens with a variety of isoelectric points and molecular weights.Some cross-reactions were demonstrated between the allergens of A. lumbricoides and Toxocara canis. On the other hand, when a passive cutaneous anaphylaxis assay was used with sera from mice sensitized by nasal inhalation of ABF plus Bordetella pertussis vaccine, it was found that only one relatively pure fraction of ABF was involved. This consisted of some of the largest protein molecules in ABF: it had a molecular weight of approximately 360000 (subunits 140000 and 220000), an isoelectric region of 8·0-8·4, and was clearly very different from the allergens isolated from ABF by other workers.ABF and its fractions need to be freshly prepared and to be kept in the presence of reducing agents to avoid rapid deterioration and irreproducibility of some results.The relatively pure allergen fraction of ABF, isolated after identification by the passive cutaneous anaphylaxis assay and tested in mice, was found to be T cell-stimulating but was non-mitogenic. Access to the circulation after intranasal administration appeared to be highly restricted.

A solid-phase radioimmunoassay was used to demonstrate that sheep with myiasis caused by the larvae of the Australian sheep blowfly, L. cuprina, had serum IgG antibodies to antigens present in an extract of the ground-up larvae. Previously struck animals demonstrated a more severe myiasis than their unstruck counterparts when both groups were subjected to a standard larval challenge. The effects of immunosuppressive therapy were expressed in terms of a decrease in the total number of larvae growing to maturity and in the area of fly strike produced.

In an attempt to differentiate virulent and benign strains of B. nodosus, the extracellular proteolytic activity of these cultures was assayed with elastin, casein and hide powder azure, and the stability to heating at 55°C was determined. Broth cultures of both strains hydrolysed 125I-labelled elastin, indicating that this activity is not a unique marker of virulence. When cultures were grown in Trypticase-arginine-serine broth medium modified by omitting Na2C03 and thioglycollic acid, the total proteolytic activity and its stability at 55°C could be used to differentiate isolates causing virulent or benign footrot lesions. However, when other broth cultures were used, these parameters could no longer be used to make such a distinction. The proteases of a virulent and benign strain of B. nodosus were partially purified and characterized. Four to five closely related proteases were detected by polyacrylamide gel electrophoresis at pH 8·8 in both types of isolates. The proteases are serine-type enzymes requiring a divalent metal ion such as calcium for activity. The proteases of the benign strain were somewhat less stable to heat than the enzymes of the virulent strain. Differences in the relative mobilities of the proteases of virulent and benign strains of B. nodosus, on electrophoresis at pH 8'8, suggest that this property may be used to distinguish virulent and benign strains.

Sheep were immunized with antigens extracted from third-instar larvae of L. cuprina. This procedure produced substantial titres of circulating antibody as measured by solid-phase radioimmunoassay or immunodiffusion or by both techniques. However, immunization did not confer protection against subsequent implant challenge with first-instar larvae. In vitro studies indicated that pooled sera from immunized sheep (mean immunodiffusion titre = 3) significantly reduced larval survival. Antigen specificity and the modulating effects of concomitant humoral responses to larval challenge are discussed in relation to the findings.