The Probiotic Mixture VSL#3 Has Differential Effects on Intestinal Immune Parameters in Healthy Female BALB/c and C57BL/6 Mice1–3

Background: Probiotic bacteria may render mice resistant to the development of various inflammatory and infectious diseases. Objective: This study aimed to identify mechanisms by which probiotic bacteria may influence intestinal immune homeostasis in noninflammatory conditions. Methods: The effect of VSL#3, a mixture of 8 probiotic bacteria, on intestinal gene expression was studied in healthy female BALB/c and C57BL/6 mice after prolonged oral treatment (28 d, triweekly) with 3 3 108 colony-forming units of VSL#3. In a separate experiment in BALB/c mice, the effects of prolonged administration of VSL#3 and of phosphate-buffered saline (PBS), followed by 1 single dose of VSL#3, on innate and adaptive immune cells were evaluated. Results:Microarray analysis of the intestines ofmice treatedwith PBS confirmedwell-established differences in the expression of immune-related genes between C57BL/6 and BALB/c mice. Prolonged administration of VSL#3 was associated with downregulation of Il13 [fold change (FC) = 0.46] and Eosinophil peroxidase (Epx) (FC = 0.44) and upregulation of Il12rb1 (FC = 2.1), C-C chemokine receptor type 5 (Ccr5) (FC = 2.6), chemokine (C-X-C motif) receptor 3 (Cxcr3) (FC = 1.6), and C-X-C motif chemokine 10 (Cxcl10) (FC = 2.8) in BALB/c mice but not in C57BL/6 mice. In BALB/c mice, it was shown that 28 d of treatment with VSL#3 affected the Peyers patches (PPs) and mesenteric lymph nodes (MLNs), which was evident from an increase in