Secret(ory) revealed: the long-awaited structures of secretory IgA

Secretory IgA (SIgA) is a specialized form of antibody present at high concentrations in mucosal secretions, where it acts as the first line of defense of the immune system. In a recent paper published in Cell Research, Wang et al. present cryo-EM structures revealing the architecture of SIgA and its interactions with SpsA, a pneumococcal adhesin that piggybacks on SIgA to facilitate gut colonization and host cell invasion by Streptococcus pneumoniae.