The diagnosis of human infection by Toxocara canis relies heavily upon serological tests, the specificity of which can be inadequate in regions of endemic helminthiasis. When different population groups of tropical Venezuela were evaluated using ELISA based upon Toxocara excretory-secretory antigen (TcESA), solid-phase adsorption of the sera with extracts of a wide variety of non-homologous parasites revealed the existence of significant cross-reactivity. This was effectively and conveniently overcome when the test sera were incubated in the presence of the soluble parasite extracts in a competitive inhibition ELISA. The mean reduction of ELISA values caused by pre-adsorption of the sera tested was 32.2%, and that caused by competitive inhibition was 42.3%, the effects of these two procedures being strongly correlated (r = 0.83). The magnitude of the reduction was inversely proportional to the actual ELISA value (r = -0.55), and ranged from a mean of 68.0% in sera from apparently healthy individuals of medium-high socio-economic level, down to 28.1% in heavily parasitized Amazon indians. Ascaris showed the greatest degree of cross-reactivity in these tests, although under conditions of competitive inhibition even sera with high levels of antibody against this parasite could be negative in Toxocara ELISA. Western blotting revealed a major 81,400 D component that was shared between Ascaris and TcESA. Our results indicate that the competitive inhibition of cross-reactivity by soluble non-homologous parasite extracts provides a convenient and economical means of increasing the specificity of ELISA for the determination of the seroprevalence of toxocariasis in tropical populations.

Immunization of a number of inbred mouse strains inraperitoneally with low levels (1–100 µg) of ovalbumin (OA) or ovomucoid (OM) in the absence of adjuvant, revealed marked strain differences in IgE responsiveness. High-OA-responder strains such as Balb/c exhibited PCA titres up to 256 in the primary response, and up to 1,280 in the secondary, while non-responders such as SJL and NZB remained PCA negative; similar variations were found in the response of the strains to OM. Repeated immunization of high-OA-responder mice with low doses of antigen without adjuvant elicited anamnestic secondary responses, but were not further boosted by tertiary stimulation. Instead, a 'persistent' high IgE response of the type previously associated with the use of specialized adjuvants, developed in these mice. Fractionation of the OA antigen by gel filtration yielded molecular species (dimers pentamers) of considerably greater IgE-immunogenicity than either monomeric OA or very highly aggregated forms. Immunization of high-OA-responder mice with the former permitted lowering of the threshold for induction of adjuvant-independent primary OA-IgE responses to a single 1.0 µg dose, and the threshold for priming to 0.1 µg.

Infection with the helminthic parasites Ascaris lumbricoides and/or Necator americanus (hookworm) induces the production in man of high levels of serum IgE. The specificity of this IgE antibody when measured by RAST to a wide range of allergens was restricted in general to the helminthic antigens. Absorption of the sera with immunosorbents produced by coupling extracts of A. lumbricoides to CNBr activated Sepharose 4B established that Ascaris antigen specific IgE antibodies contributed a minor fraction of the total serum IgE. These observations suggest that parasitic infections in man as in laboratory animals potentiate the production of high levels of IgE with specificity unrelated to that of the parasite antigens. While the specificity of this potentiated IgE was not established, it is not directed towards inhalant allergens.

The assessment of IgE production in cultures of T- and B-cells from peripheral blood is proving a useful tool to probe IgE immunoregulation in human atopies. The present study contrasts secretion and synthesis as indices of IgE production, and demonstrates that these measures yield comparable data upon the magnitude and direction of regulatory T-cell effects (help vs. suppression) in severe atopies. The majority of peripheral blood B-cell samples from the atopies in this study exhibited spontaneous IgE synthesis and secretion, and in vitro T-cell help and suppression were observed with equal frequency within the sample population. Repeated testing of individual atopies indicated that the direction of T-cell effects remained stable in some (but not all) atopies over periods as long as 3 years.

An enzyme-linked immunosorbent assay (ELISA) was used to determine the seroprevalence of Toxocara canis infection in different socio-economic groups of the tropical population of Venezuela. The lack of definitive independent diagnostic criteria for toxocariasis required the establishment of operational upper limits of normality for Toxocara ELISA values, based upon their log-normalized distribution in a presumptive "non-toxocariasis" sub-population. Only 1.8% of urban subjects of medium-high socio-economic level were considered to be clearly positive in Toxocara ELISA, compared to 20.0% of urban slum dwellers, 25.6% rural subsistence farmers and 34.9% Amazon Indians. As the test was performed using excretory-secretory antigen, and under conditions of competitive inhibition by soluble extracts of non-homologous parasites, co-infection by common intestinal helminths, protozoa or other organisms did not give rise to false positive results. However, strong cross-reactivity with Onchocerca volvulus may have influenced the prevalence figure obtained for the Amazon Indians. These results indicate that T. canis is yet another parasite that is widely distributed in economically underprivileged tropical populations.

The floating fraction of egg yolk (90% lipid, density 0.98) appears to be heterogeneous but no significant fractionation took place during centrifugation in several solvents of density 0.98 or higher. This fraction had a particle size several times that of the lipoprotein (50% lipid) remaining after ether extraction. Most of the so-called "free" lipid extracted by ether is apparently part of, or associated with, the lipoprotein.The lipid-free vitellenin was not soluble in mild aqueous solvents and most of the physical measurements were made in 88% formic acid solutions. Molecular weights ranged from 3.0 to 9.0 × 104. The higher value, considered most reliable, was only half the estimated size of the protein part of the lipid-containing materials. Evidently the protein portion of the lipoprotein has two or more polypeptide chains that may be combined directly or through lipid by forces weaker than the peptide linkage.

Intestinal immunoglobulin levels were quantitated in undernourished Indonesian children with enteric infections and normally nourished Indonesians with and without enteric infections. These were compared to the same parameters in Australian Aboriginal children (also suffering undernutrition) and normal Caucasian children. Children with enteric infections displayed equally elevated levels of intestinal immunoglobulin irrespective of their nutritional status. Intestinal infections appeared to elevate IgG levels more than secretory IgA levels in the age group examined. However, it appeared likely that some of the EgG was serum-derived whereas the IgA appeared to be locally produced. There was no apparent deficiency in the capacity of undernourished children to manufacture and secrete immunoglobulin in the gut.

The prevalence of asthma in a population of the South Fore linguistic group of the Eastern Highlands Province of Papua New Guinea has shown a remarkable increase in the last decade and is now 7.3% in adults and 0.6% in children. Allergy to house dust mite appears to play a major role in the disease pathogenesis. The low childhood prevalence may be associated with endemic parasitism which operates by suppressing production of IgE antibodies to ubiquitous allergens. This suppression is significantly correlated with age in boys of 6–20 years, but not for girls who retain low serum titres throughout the entire age range. Bronchial reactivity, assessed by histamine inhalation test, does not identify asymptomatic children who may be potential asthmatic subjects suggesting that, in this population, bronchial hyperreactivity follows the development of immunological hypersensitivity.