Immunoadjuvant activity of oralLactobacillus casei: influence of dose on the secretory immune response and protective capacity in intestinal infections

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Abstract
Summary: Lactobacilli, often used as effectors of host functions, could play an important role in maintaining human health by controlling other intestinal microorganisms capable of producing harmful effects. Using an experimental model, we studied the effect of different oral doses ofLactobacillus caseion the secretory IgA response and the protective capacity of the microorganism in preventing intestinal infections. The optimization of the protective dose ofLb. caseiby previous feeding and the use of the lactobacillus as an immunological way to control enteric infections were investigated. We found that conventional mice were protected against infection withSalmonella typhimuriumandEscherichia coliby previous feeding for 2 consecutive days with a dailyLb. caseidose of 1·2 × 109cfu/mouse. Previous feeding for 7 d proved less effective, and feeding for 5 d afforded no protection at all. We were also able to demonstrate that the protective effect ofLb. caseiagainstSal. typhimuriumandEsch. coliwas connected mainly with the high level of IgA antipathogen antibodies present in intestinal secretions. β-Glucuronidase (EC 3.2.1.31) and β-galactosidase (EC 3.2.1.23) activities, measured both in the intestinal fluid and histological samples, showed a marked increase in intestinal inflammatory response on day 5 of feeding. These results show thatLb. caseiplays an important role in the prevention of enteric infections, a low dose being enough for protection against intestinal infections by increasing IgA secretion into the intestinal lumen, thus providing adequate defences for the mucosal surface. A previously administered dose of this magnitude could therefore be used as an oral adjuvant in preventing enteric infections.