With great interest I’ve read the recent publication in Immunity that alters our current understanding of when class switch recombination (CSR) occurs. It was always believed that CSR and Somatic Hyper Mutation (SHM) occurred within the germinal center, but Roco et al. show that CSR actually occurs prior to germinal center formation and extrafollicular plasmablast induction. Signs of CSR can be detected as early as 1.5 days following immunization. This result explains why many IgM memory B cells can be found, as if CSR occured in the germinal center they would likely be skewed towards the same isotype. Overall, this new insight alters our current dogma of when we believe CSR occurs and opens up a specific window of when we could specifically intervene with CSR.

I briefly highlighted this new finding in a breaking news item on Immunopaedia, promoting immunology education worldwide.