Sir,Entamoeba gingivalis and Trichomonas tenax are human buccal protozoa. They live in dental tartar, in the necrotic mucosa of the cells and the gingival fringes of the gums 6 .The complexity of the oral environment and the multifactorial nature of the caries lesion, with the consequent loss of dental pieces, requires the cooperation of other disciplines such as Microbiology, Chemistry and Dietetics. Both partial and total loss of dental pieces produce modifications in buccal biotic conditions 1 . Some investigators think that E. gingivalis is an agent which causes periodontitis 7 , while others consider it an opportunist capable of survive in the medium induced by periodontal disease 5 .T. tenax, in spite of being considered as a commensal might take part in the first phases of the process of destruction of periodontal tissues 6 owing to the finding of an acid phosphatase 3 , a surface protein similar to fibronectine 6 and an important collagenolytic activity 6 .The objetive was to determine the frequency of these two protozoa and their relation with salivary IgA and with salivary pH in patients with dental prothesis.Fifty adult patients with either fixed or mobile prothesis were selected. Tartar and/or dental plaque samples of the 4 inferior incisors were obtained by means of a scaler, as well as a saliva sample was taken from each of the patients. Both were collected in the morning with no previous brushing or, in other cases, after a period of at last three or four hours after the last buccal hygiene.Tartar, as well as dental plaque were diluted with sterile physiologic solution and was observed through an optical microscope (100x and 400x).There was a previous microscopic observation of saliva followed by another observation after 2000 r.p.m. centrifugation during 5 minutes (100x and 400x) to identify protozoa.Both samples were coloured with Gomori trichromic stain 11 and cultured at 37 °C in the following specific media: Bacto Endamoeba Medium for E. gingivalis and Diamond medium 4 for T. tenax. Cultures were daily observed for 72 hours.In saliva samples, pH was determined by means of strips of indicant paper (V.N.: 6/0-7/5), and secretory IgA concentration was determined by the radial immunodiffusion method 10 (V.N.: 20-40 mg/dl).The statistical analysis was performed by the χ 2 test (signification level 0/05) so as to study the association between pH and IgA with the presence of parasite 2 .Out of the 50 examined patients, 36 (72%) presented parasites, 29 were monoparasitized, 26 presented E. gingivalis and 3 presented T. tenax; the other 7 presented both protozoa.The frequency of E. gingivalis in the population studied was 66% and 20% for T. tenax. Both protozoa were predominant in the tartar sample, and/ or the dental plaque.The cultures performed for the search of T. tenax increased significantly the diagnostic sensitivity, since out of the 10 positive patients, 5 were diagnosed only through the culture. However, for E. gingivalis, neither the culture nor the trichromic coloration increased sensitivi...

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 3,5,9 .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. 2 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 a antigen by Schistosoma mansoni 4,6,8 .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 1,7 .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.

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