Toxoplasma gondii infects humans through the gastrointestinal tract (GIT), which elicits humoral immune response with specific antibodies. The expression of the ABO blood group glycoconjugates also occurs in this same system and may influence the human susceptibility of infection by T. gondii. The aim of the present study was to investigate the association between ABO blood group phenotypes and the presence of anti-T. gondii antibodies. Data - including age, results of serology tests for T. gondii infection and ABO blood group phenotypes - were assembled from the medical records of 1,006 pregnant women attended in the Base Hospital of the Medical School of São José do Rio Preto, Brazil, between 2001 and 2004. The chi-square test was used to compare the results with the level of significance set at 5%. Of the studied cases, 64.1% (645/1006) and 35.9% (391/1006) presented respectively positive and negative serology tests for anti-T. gondii antibodies. The mean age of those who tested positive was higher than those with negative serology tests (p = 0.0004). The frequencies of ABO blood group phenotypes were similar in those with and without anti-T. gondii antibodies (p = 0.35). In conclusion, the ABO blood group system is not associated with the presence or absence of anti-T. gondii antibodies.

Diseases resulting from Helicobacter pylori infection appear to be dependent on a host of genetic traits and virulence factors possessed by this microorganism. This paper aimed to investigate the association between the ABO histo-blood groups and H. pylori cagA infections. Genomic DNA samples (n = 110) of gastric biopsies obtained from patients with endoscopic diagnosis of peptic ulcers (n = 25) and chronic active gastritis (n = 85) were analyzed by PCR using specific primers for the cagA gene. Of the samples, 66.4% (n = 73) tested positive and 33.6% (n = 37) negative for the gene. The cagA strain was predominant in peptic ulcers (n = 21; 84.0%) compared with chronic active gastritis (n = 52; 61.2%) (p = 0.05; OR 3.332; 95% CI: 1.050-10.576). Additionally, the cagA strain was prevalent in the type O blood (48/63; 76.2%) compared with other ABO phenotypes (25/47; 53.2%) (p = 0.01; OR 2.816; 95% CI: 1.246-6.364). These results suggest that H. pylori cagA infection is associated with the O blood group in Brazilian patients suffering from chronic active gastritis and peptic ulcers.