Secretory and humoral antibody responses to Blastocystis hominis in symptomatic and asymptomatic human infections.

The study included 3 groups of individuals, in the first 2 groups they had positive stool microscopic examinations only for B. hominis indicating blastocystosis, with and without gastrointestinal symptoms, respectively, while the last group included apparently healthy individuals with no parasites in stool. Stool and serum samples of these individuals were subjected to detection of anti-B. hominis fecal and serum IgA and serum IgG antibodies by indirect ELISA, and detection of B. hominis fecal and serum antigens by double sandwich ELISA. In symptomatic B. hominis infections with positive stool microscopy the study recorded first: specific secretory IgA and humoral IgA and IgG antibody responses at a prevalence of 100%, 83.3% and 86.6%, respectively, with an increased significant difference (P<0.001) of each from healthy controls, together with an increase in level of secretory IgA than that of humoral IgA antibody (P<0.001), and second: the presence of specific antigens in stool and serum at a prevalence of 96.6% and 90%, respectively. With an increased significant difference (P<0.001) of each from healthy controls together with the former at a higher level than the latter (P<0.05). In asymptomatic B. hominis infections with positive stool microscopy the study recorded first; absence of each of the studied specific secretory and humoral antibody responses with no significant difference (P>0.05) of each from healthy controls, and second; absence of specific antigens in stool and serum with no significant difference (P>0.05) of each from healthy controls nor from each other. The explanations and implications of these results are discussed.