Effect of aging on antibody production against the receptor binding domain of Clostridioides difficile toxin B in a murine model

Clostridioides difficile is a spore producing, gram positive, anaerobic bacillus which produces toxins and causes antibiotic associated diarrhea. The main risk factor for infection is disruption of the normal gut flora from antibiotic use, allowing overgrowth of C. difficile in the colon. Toxins can cause severe diarrhea and pseudomembranous colitis. Current therapies for acute infection are Fidaxomicin, Vancomycin, or Metronidazole. C. difficile infections (CDI) are an urgent problem, and developing effective vaccines should be a priority. The current aim of vaccine development has surrounded the receptor binding domain of the toxin B protein (rTcdB) because of its increased immunogenicity and non-toxicity. CDI are frequently acquired in hospitals and nursing homes, leaving the elderly population at a higher risk of developing CDI. Additionally, immunosenescence, decreased immune functioning in older individuals, only furthers their risk. Given that most murine vaccine studies use younger mice, and the increased risk of severe infection in the elderly, it is important that the efficacy of any vaccine be tested in this population. Our lab has studied the effect of aging on IgG production against rTcdB protein in a murine model. In our pilot study, we vaccinated young (6 weeks old) and elderly (72 weeks old) C57BL/6 mice with purified recombinant protein corresponding to the receptor binding domain of C. difficile toxin B (rTcdB). Each mouse received by intraperitoneal injection of 3 doses of 20µg rTcdB mixed with Alum or saline only. Our study showed that in both young and elderly mice, rTcdB vaccination induced antigen specific IgGs in serum collected 2 weeks post vaccination. Interestingly, our novel study showed a decreased IgG response in older mice when compared to the younger group, which could indicate a decreased defense against C. difficile infection in older mice. Our study suggests that the immune system of elderly individuals may not respond as robustly against rTcdB, which could reduce the efficacy of a vaccine based on this protein. More work can be done to investigate how to support gut microbiota and reduce severity of acute CDI in at risk populations. We are currently working on exploring the role of micronutrient supplementation to improve vaccine efficiency.