Lactobacillus rhamnosus GG is the most studied and well-characterized probiotic strain, it was patented 30 years ago. It produces lactic acid, it ferments rhamnose. It is able to survive to gastric acidity and bile salts, to adhere to the intestinal mucosa, it modulates the immune system and epithelial cells apoptosis.
The beneficial properties of LGG on human health are exerted on various levels. Indeed, it has a strong anti-inflammatory activity, it contributes to the intestinal barrier integrity, it is highly effective as antidiarrheal, also in children, it counteracts the proliferation of pathogens as Helicobacter pylori and Escherichia coli, it is useful in immune deficiencies related to respiratory health, it promotes oral health.
LGG was tested in many clinical studies in ulcerative colitis patients to evaluate its ability to induce and maintain the remission of tis severe disease, which is classified among the Inflammatory Bowel Diseases (IBD).
Zocco and colleagues (2006) tested LGG in comparison to mesalazine, the most common anti-inflammatory drug used in this contest, to test its ability to maintain ulcerative colitis remission. 187 patients in remission from less than 12 month have been treated with LGG (1.8*1010 UFC/day) or mesalazine (2400 mg/day) and for 12 months they were monitored to understand how many of them keep the remission or relapse. The study reveals that there are no differences between the two treatments, and, in conclusion, the probiotic has the same efficacy of mesalazine in maintaining ulcerative colitis remission. Moreover, it was observed that the treatment with LGG seems to be more effective than the standard treatment with mesalazine in prolonging the relapse-free time.

A secondo study, performed by Pagnini and colleagues (2023) evaluated the potential role of LGG as maintaining therapy in patients with ulcerative colitis with mild–moderate clinical activity. 75 patients have been treated with LGG (12*1010 UFC/day) for 4 weeks, after a wash-out period from mesalazine of 4 weeks. At the end of the treatment it was evaluated how the disease clinical score has evolved and, between the 55 patients who completed the study, 58% has improved its condition, 38% was stable and 4% (corresponding only to 2 patients) worsened. Among those who improved their condition, 54% entered in remission.

These studies show some of the great therapeutical applications of Lactobacillus rhamnosus GG, also as adjuvant in the treatment of severe diseases as ulcerative colitis.
References
Pagnini, C., Di Paolo, M. C., Urgesi, R., Pallotta, L., Fanello, G., Graziani, M. G., & Delle Fave, G. (2023). Safety and Potential Role of Lactobacillus rhamnosus GG Administration as Monotherapy in Ulcerative Colitis Patients with Mild–Moderate Clinical Activity. Microorganisms, 11(6), 1381.
Zocco, M. A., Dal Verme, L. Z., Cremonini, F., Piscaglia, A. C., Nista, E. C., Candelli, M., … & Gasbarrini, A. (2006). Efficacy of Lactobacillus GG in maintaining remission of ulcerative colitis. Alimentary pharmacology & therapeutics, 23(11), 1567-1574.