Administration of exogenous IL-22 to mice with influenza causes the upregulation of genes encoding proteins involved in cell-cell adhesion such as Cldn24 and Pcdh15 (encoding claudin 24 and protocadherin 15, respectively) in the lungs, and reduces systemic dissemination of S. pneumoniae during secondary bacterial infection (174). Here, PCDH15 is linked to bacterial infectious disease.