Location, location, location: B-cell differentiation in the gut lamina propria

The intestinal immune system includes an immunoglobulin (Ig)A-inductive site represented by Peyer's patches (PPs) and an IgA effector site represented by the lamina propria (LP). This canonical map of intestinal IgA production has been blurred recently by studies showing the presence of active IgA class switching in the LP. Here we discuss the functional implications and controversial nature of these findings.