Immunoglobulin gene mutation patterns and heterogeneity of marginal zone lymphoma

Marginal zone (MZ) or MZ-like B-cells "home" outside the follicles of peripheral lymphoid tissues. Prototypic examples of these B-cells are those that home the MZ of the spleen, although B-cells with similar phenotypic and functional features can be found in the subepithelial (SE) areas of tonsil, in the Peyer's patches, in the lymph nodes, and in the thymic medulla. MZ-like B-cells also develop in mucosa-associated lymphoid tissue (MALT) and other sites (salivary glands, thyroid) that acquire organized lymphoid tissue after chronic antigenic stimulation, such as Hp infection in gastric maltomas or autoimmune insult in Sjogren's syndrome. Beside the so-called extranodal B-cell MALT lymphoma, the splenic MZ lymphoma with or without circulating villous lymphocytes and monocytoid lymphoma also are thought to originate from MZ B-cells. Normal MZ-like B-cells can be isolated from different tissue sources (tonsil, spleen) by using combination Percoll gradients, magnetic fractionation, and fluorescence-activated cell sorting. Analyses of morphology, phenotype, and functions of these purified MZ B-cells demonstrated that in humans, MZ B-cells are rather heterogeneous, comprising virgin and memory B-cells and of cells specialized in different types of human responses. In this chapter, we review the main procedures used to isolate and test the phenotypic and functional features of the MZ B-cells from human tonsil and spleen in our laboratory and discuss their characteristics by comparing them with the MZ B-cell-derived lymphomas.