Juana Valverde

Preliminary studies on antigenic mimicry of Ascaris lumbricoides

Sir, During the last twenty years there has been an increasing number of publications in which the fact that blood group antigens may act as parasite, bacterium and virus receptors is remarked. Three concepts have been proposed to explain hosts tolerance for a parasite: mimicry, antigenic modulation and natural selection. The early experimentations which led to the comprehension of the concept of mimicry were performed by CLEGG et al. on Schistosoma mansoni. They demonstrated that larvae in culture may capture A and B antigens and get covered by them. Later investigations based on immunofluorescence and mixed agglutination techniques have demonstrated in vitro adsorption of H, A, B and Le antigen by Schistosoma mansoni . In order to perform our experiments Ascaris lumbricoides extracts (AE) were prepared. Adult specimens were washed in physiological solution supplemented with 200 μg/ml of streptomycin and 200 μg/ml of penicillin. After that a refrigerated mechanical rupture was performed for 5 days. The supernatants were collected and kept at –20 °C with a final concentration of timerozal 1:1,000. Inhibition agglutination tests were made facing the (AE) against anti A and anti B monoclonal antibodies in optimal concentrations. Suspensions of fresh red cells (A and B groups) were used as a revealing system. Results demonstrated that (AE) of patients having blood group A inhibit agglutination of anti A antibodies with A red blood cells, and (AE) of patients who have blood group B inhibit agglutination of anti B antibodies with B red blood cells. In a second experience these (AE) were faced against sera of patients suffering from ascariasis. (AE) of blood group A patients were found to inhibit agglutination of anti A antibodies with A red blood cells of patients group B (anti A) as well as (AE) of blood group B patients were found to inhibit agglutination of anti B antibodies with B red blood cells of patients group A (anti B). These preliminary experiences suggest that Ascaris lumbricoides may adsorb A and B antigens of the host for antigenic mimicry. Current investigations have a definitive objective: to determine the moment in the life cycle of a parasite in which this adsorption takes place. It might probably be in larval stages in which the parasite moves following the haemetic way.

ABO System: molecular mimicry of Ascaris lumbricoides

A. lumbricoides has been associated to the ABO System by various authors. The objective was to detect ABO System epitopes in A. lumbricoides of groups O, A, B and AB patients. 28 adult parasites were obtained from children to be used as assay material. The patients ABO blood groups were determined. Extracts of A. lumbricoides [AE] were prepared by surgical remotion of the cuticle and refrigerated mechanical rupture. Agglutination Inhibition (AI) and Hemoagglutination Kinetics (HK) tests were used with the [AE]. Of the 28 [AE], eight belonged to O group patients, 15 to A group, three to B group and the remaining two to AB children. The AI Test showed A epitopes in two [AE] of group A patients and B epitopes in two [AE] of group B patients. The HK Test showed B antigenic determiners in two [AE] of group B patients and in two [AE] of group AB patients as well as A antigenic determiners in one [AE] of A group patient. Of the 28 [AE] studied in both tests B epitopes were detected in all [AE] from B and AB patients and A epitopes in three of the 15 [AE] of group A patients. The experiments carried out suggest that A. lumbricoides might absorb A and B antigens from the host, and/or modify the cuticular carbohydrates expression as a kind of antigenic mimicry.

Ascaris lumbricoides: alteration of the erythrocyte superficial charge using the Partition Method in aqueous two-phase system

Sialic acid is responsible for the negative charge of the erythrocyte. The decrease of sialic acid has hemodynamical and hemorheological importance. The aim was to study the effect of A. lumbricoides on the erythrocyte superficial charge using the Partition Method in aqueous two-phase system in order to indirectly evaluate the alteration of sialic acid in the red cells. We worked with five parasite extracts (AE) and larvae concentrate (LC). Erythrocyte superficial charge was studied by working with non-treated (Controls) and treated erythrocytes. The treatment consisted of incubating the erythrocytes with AE or LC for 30 minutes at 4 degrees C, 20 degrees C and 37 degrees C. The red cells were separated in a sensitive charge two-phase system (Dx/ PEG). The partition coefficient (P) of treated and untreated erythrocytes were calculated. The results showed a P decrease at the three temperatures for red cells treated with four of the AE. The remaining extract did change P values at any of the temperatures studied. The erythrocytes treated with LC showed a decrease in the P value at 37 degrees C and 4 degrees C but no change was observed at 25 degrees C. Statistical analysis concluded that P values were significantly lower in treated erythrocytes than in their corresponding untreated ones (p < 0.05). The Partition Method showed that this parasite alters the erythrocyte superficial charge which may indicate that it can catch sialic acid.

P System antigenic determiners expression in Ascaris lumbricoides

The P System antigens have been detected in numerous parasites, bacteria and viruses, nevertheless the clinical significance is still unknown. The aim was to study the presence of P1 antigenic determiners in A. lumbricoides extracts by means of the use of 6 different monoclonal antibodies of well-known concentrations and Ig class. We worked with 14 A. lumbricoides extracts. Inhibition Agglutination Test was made in a bromelin enzymatic medium and 4 degrees C temperature. Titre, Score and Sensitivity Parameter were determined for each monoclonal antibody against red cells suspension used as revealing system. Ten extracts inhibited the agglutination of all anti P1 monoclonal antibodies. The 4 remaining extracts only inhibited the agglutination of some of them. It is demonstrated that the extracts have P1 activity. This activity is independent of titre, Score, Sensitivity Parameter, concentration and Ig class and it depends on the epitope at which the monoclonal antibody is directed.