Age-associated defects impair the optimal development of a protective immune response to Clostridium difficile in the context of infection in a novel aged murine model

Abstract

Abstract Clostridium difficile infections (CDI) is a major source of mortality in the US, especially among the elderly. Protection against CDI is mediated by anti-toxin host antibodies (Ab). Although it is known that elderly mount an impaired anti-toxin response, it is yet to be determined whether their lower Ab levels are due to defective germinal center (GC) priming during acute CDI that leads to defective B cell proliferation and maturation. To test our hypothesis, we developed an antibiotic mucosal spore challenge CDI model and infected young (4mo.) and aged (>18mo.) mice with UK1 hypervirulent C. diff spores. By day 4 post-infection 100% of the aged had succumbed to infection compared to only 10% of young mice. Following a sublethal spore challenge a significant decrease of total PD1+CXCR5+ Tfh cells was detected in aged compared to young at Day 12 and 21 PI (p< 0.05 and p< 0.03, respectively). We also observed a marked decline of total and antigen-specific CD19+PNA+CXCR5+ B cells in our aged cohort (p< 0.05). We re-challenged with a lethal dose 1 month later. Only 50% of the aged vs 100% of the young survived. At Day 7 post re-challenge (D37) there was a decrease in total GC B cells (M= 7.2% SD+/−1.8 in aged vs M=15.8% SD+/−3.3 in young) and no change in Tfh cells (M= 7.5% SD+/−0.7 in old vs M=8.2% SD+/−2.1 in young). Further, the frequency of anti-toxin-specific B cells was significantly decreased in the aged (p= 0.02). The frequency of toxin-specific IgG, IgM and IgA ASC, and serum and mucosal toxin-specific Ab were markedly reduced in the aged. Our data suggests aged mice are more susceptible to CDI due to a defect in early GC formation, leading to an impaired antigen-specific Ab response. Overcoming this could prevent age-associated recurrence and severe CDI.