Читать книгу Pathology of Genetically Engineered and Other Mutant Mice - Группа авторов - Страница 115

Lymphoid tissue can be divided into primary, secondary, and tertiary lymphoid tissues. The primary lymphoid organs are the sites of development and maturation of B and T lymphocytes. The developing B and T lymphocytes undergo somatic recombination of the immunoglobulin and T cell receptor gene segments resulting in a vast repertoire of antigen‐specific receptors. This process is largely antigen‐independent. The primary lymphoid organs in the mouse are the bone marrow for B cell development and the thymus for T cell development. The initiation of the adaptive immune response mediated by antibodies and T cells occurs in the secondary lymphoid organs which include the lymph nodes, white pulp of the spleen, and mucosa‐associated lymphoid tissues. Mature, naïve B and T lymphocytes circulate through the secondary lymphoid organs which are connected via the lymphatic and blood circulation. Naïve lymphocytes enter the lymph nodes and mucosa‐associated lymphoid tissues via high endothelial venules and leave via the efferent lymphatics. The spleen has open‐ended arterioles that deliver lymphocytes to the marginal zone and red pulp. Lymphocytes leave the spleen primarily via the splenic vein. The restricted circulation pattern of naïve lymphocytes maximizes the chances that the few lymphocytes with receptors for a specific antigen will encounter that antigen which is delivered to the lymphoid tissues. Lymph nodes are strategically positioned throughout the body to capture antigens delivered via the afferent lymphatics from the tributary areas. Blood‐borne antigens are captured by macrophages, B cells and dendritic cells in the marginal zone of the spleen and transported into the white pulp. The epithelium that overlies the mucosa‐associated lymphoid tissues has specialized epithelial cells (M cells) that facilitate the uptake of antigens from the mucosal surface and transport them into the underlying lymphoid tissue.

Tertiary lymphoid organs develop at sites of chronic inflammation associated with infections, autoimmune disease, and cancer. The organization of tertiary lymphoid organs mimics that of secondary lymphoid organs with varying degrees of differentiation.