Cover picture: Immunofluorescence staining of IgA (green) and IgG (red) with blue nuclear staining in a cross-section of the crypt region from the small intestine of a polymeric Ig receptor knockout (pIgR-/-) mouse. Only the nuclei of the epithelial cells are seen because the (pIgR-/-) mice fail to actively transport IgA to the gut lumen (picture taken by Takeshi Yamanaka). See related article in this issue by Johansen et al., pp. 915921.
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