Effect of growth conditions of Lactobacillus gasseri OLL2809 on the immunostimulatory activity for production of interleukin-12 (p70) by murine splenocytes

Lactobacillus gasseri OLL2809, a probiotic lactic acid bacterium, strongly stimulates interleukin (IL)-12 (p70) production by murine splenocytes; therefore, it is expected to ameliorate allergic diseases. Although many studies have investigated characteristics of the immunostimulatory activity of probiotics, little is known about how bacterial growth conditions affect the activity. In this study, we investigated the effects of the growth conditions of L. gasseri OLL2809 on the stimulation of IL-12 (p70) production. L. gasseri OLL2809 was grown under various culture conditions including different cultivation periods, media, and culture pH, and IL-12 (p70) production by murine splenocytes stimulated with these bacterial cells was determined. The results revealed that IL-12 (p70) production (i) increased with the growth of the bacterial cells and was higher in stationary-phase cells than in logarithmic-phase cells; (ii) it was higher in the cells grown in acidic pH; and (iii) it decreased when the cells were incubated in a buffer at neutral pH prior to heat treatment. These observations indicated that stimulation of IL-12 (p70) production is affected by culture medium pH. In addition, the observations of a difference in the stimulation of IL-12 (p70) production by L. gasseri OLL2809 grown under various conditions are consistent with the characteristics of autolysis. Therefore, it was deduced that the integrity of the bacterial cells is necessary for the stimulatory effect on IL-12 (p70) production and that acidic pH and heat treatment contributed to the stimulation by inhibiting the activity of autolysins indigenous to the bacteria. Our result suggests that cultivation until the stationary phase under acidic pH is required for the effective production of probiotics with immunostimulatory activity.