Effect of mature lymphocytes and lymphotoxin on the development of the follicle-associated epithelium and M cells in mouse Peyer's patches.

BACKGROUND AND AIMS: Mechanisms regulating M-cell formation are still poorly understood. In vitro studies showed that lymphocytes trigger the conversion of enterocyte cell lines into M cell-like cells on coculture, whereas in vivo their role in M cell differentiation is still elusive. Our aim was first to examine Rag-1-/- mice, lacking B and T lymphocytes, for the presence of intestinal M cells. Second, we investigated the role of lymphotoxin alphabeta signaling on M-cell formation, given its pivotal role in the development of mouse Peyer's patches. METHODS: Small intestines of Rag-1-/- mice, injected or not with soluble lymphotoxin beta receptor-immunoglobulin fusion protein, were analyzed morphologically using whole mount cytochemical staining, immunohistochemistry, and electron microscopy. RESULTS: Small Peyer's patch-like aggregates were found in Rag-1-/- mice in normal number and location. The overlying epithelium of such aggregates was reduced in size but still harbored M cells. In vivo neutralization of lymphotoxin beta-receptor signaling partially reduced the percentage of M cells. CONCLUSIONS: The absence of mature lymphocytes does not prevent the formation of M cells, indicating that the signaling molecules that support M-cell differentiation, such as lymphotoxin alphabeta, may also be supplied by non-B and non-T cells. Mature B lymphocytes, however, are required for the formation of a full-sized follicle-associated epithelium.

Transient expression of M-cell phenotype by enterocyte-like cells of the follicle-associated epithelium of mouse Peyer's patches.

BACKGROUND & AIMS: The follicle-associated epithelium (FAE) over mucosa-associated lymphoid tissues consists of distinct enterocytes and M cells concentrated at its periphery. The basement membrane composition was analyzed to test whether differences account for the distinct differentiation programs along the crypt-villus and crypt-FAE axes. To determine whether the decreased number of M cells in the FAE apex is caused by premature extrusion, we mapped the site where they undergo apoptosis. METHODS: The FAE basal lamina of Peyer's patches from BALB/c mice was analyzed by immunochemistry. M cells were identified using the Ulex europaeus agglutinin lectin. The cell proliferation and apoptotic compartments were characterized using bromodeoxyuridine incorporation and the TUNEL assay. RESULTS: The perlecan and laminin 2 stainings were different in FAE and villi. Myofibroblasts were absent beneath the FAE. The migration kinetics of cells along the FAE was similar to that along the villi. Apoptotic cells were detected exclusively at the apex of the FAE. CONCLUSIONS: FAE and M-cell differentiation is associated with a distinct basal lamina composition. FAE enterocytes express transient M-cell features as they move from the crypts toward the apoptotic compartment. M cells have a highly plastic phenotype that raises interesting questions about the control of intestinal epithelial cell differentiation.

Development of Peyer's patches, follicle-associated epithelium and M cell: lessons from immunodeficient and knockout mice.

Studies with immunodeficient and knockout mice have revealed that the development of mucosa-associated lymphoid tissues (MALT) and peripheral lymphoid nodes share common mechanisms, but also require distinct signals. Gene disruption of lymphotoxins or their cognate receptors affects both Peyer's patch and lymph node organogenesis. Disruption of the osteoprotegerin TNF-family member gene does not impair Peyer's patch development, but prevents formation of peripheral lymph nodes. Peyer's patch do not form in mice with a deleted gene encoding a B lymphocyte-specific chemokine receptor, while most peripheral lymph nodes, except inguinal, are normal in numbers and architecture. In B or T lymphocyte-deficient mice, Peyer's patches, with their overlying follicle-associated epithelium (FAE), are present although reduced in number and size. No Peyer's patches develop in RAG deficient mice. Formation of FAE with typical M cells has not been analyzed in these mice. M cell formation requires the close association of immune cells with differentiated enterocytes and their conversion appears to be transcriptionally regulated. The development of MALT, FAE and probably M cells is a multistep process that requires signalling pathways common to all secondary lymphoid tissues, but also MALT-specific factors.

Intranasal immunization with SAG1 protein of Toxoplasma gondii in association with cholera toxin dramatically reduces development of cerebral cysts after oral infection.

SAG1 protein of Toxoplasma gondii was evaluated as a protective antigen in mucosal immunization with cholera toxin as an adjuvant. CBA/J mice intranasally immunized with a combination of SAG1 and cholera toxin exhibited significantly fewer cysts in the brain after oral infection with the 76K strain of T. gondii than control mice. This acquired protection lasted at least 5 months. Protected mice developed high levels of serum anti-SAG1 immunoglobulin G antibodies as well as an enhanced systemic cellular response, as assessed by the proliferation of splenocytes in response to SAG1 restimulation in vitro. This cellular proliferation was associated with an increase of interleukin-2 and interleukin-5 synthesis and with barely detectable gamma interferon production. Splenic immune T cells were shown to convey modest protection to recipients against development of brain cysts following oral infection with T. gondii. Significant production of anti-SAG1 immunoglobulin A was induced in intestinal secretions of protected mice. These results indicate that intranasal immunization with SAG1 and cholera toxin can induce mucosal and systemic immune responses and affords partial and long-lasting resistance against the establishment of chronic toxoplasmosis.