Normal Development of the Gut‐Associated Lymphoid Tissue Except Peyer's Patch in MyD88‐Deficient Mice

MyD88 is a key adaptor molecule for signalling via Toll‐like receptors (TLRs) and the response to gut commensal microbes. To investigate the role of TLRs/MyD88 pathway in the development of the gut‐associated lymphoid tissue (GALT), we examined the development of Peyer's patches (PPs) and cryptopatch (CP), and also one of effector compartment, intraepithelial lymphocyte (IEL) in MyD88 –/– , TLR2 –/– and TLR4 –/– mice. In MyD88 –/– mice, the organogenesis of PPs was not disturbed. However, PPs in 2‐week‐old MyD88 –/– mice were significantly smaller than those in MyD88 +/– mice. Also, in 2‐week‐old TLR4 –/– , but not TLR2 –/– mice, PPs did not develop rapidly. The development of PPs in MyD88 –/– and TLR4 –/– mice was completely recovered in 10 weeks. PP cells from MyD88 –/– mice showed significant decrease in proliferation when stimulated with lipopolysaccharide. The development of CP and IEL was also normal in 10‐week‐old MyD88 –/– mice. These results suggest that the TLRs/MyD88 pathway might be involved in the development of PPs only at early postnatal stage, and TLRs/MyD88‐independent signalling is critically involved in the development of GALT in adult mice.