Pre-activation of follicular B cells in old mice generates a hyper-response during germinal center reaction.

Abstract

Abstract Immune cells acquire a variety of defects that accumulate overtime in a process known as Immunosenescence. To study any innate defects that B lymphocytes may acquire during aging, we have developed an adoptive transfer system using follicular B cells from young (FO Y, 8–12 weeks) and old (FO O, >22 mo.) mice into a μMT B cell-deficient mouse. This model reveals that FO Ocells, compared to their young counterparts, produce a higher amount of activated germinal center (GC) B cells in the presence of the common antigen NP-CGG after 14 days of immunization. However, these cells do not produce antigen-specific antibodies while showing a significant decrease in NP+ λ+ antigen-specificity. To study this change in phenotype further, we performed single cell RNA sequencing using both young and old populations of naïve, and day 14 GC B cells. Comparison of the naïve populations by PCA showed only minor differences between populations. Interestingly, Ccr6is being upregulated in FO Ocells but has a decreased expression in the old population of GCs. This change in expression suggests that FO Ocells are pre-activated before transfer to μMT mice and antigen encounter. Analysis of the immunoglobulin repertoire in these cells showed that FO Ocells also have decreased use of the canonical NP-specific IgH V-gene 1–72 and fail to include the CDR2 W33L mutation that is known to increase antibody affinity 10-fold. Taken together, these findings show that old mice produce pre-activated and hyper-responsive cells that cause a lack of proper selection and affinity maturation during the GC reaction. This research was supported in part by the Intramural Research Program of the NIH, National Institute on Aging.