Heterogeneity of memory marginal zone B cells in the rat
The spleen is an important organ of the immune system. Like other lymphoid organs, the spleen is compartmentalized. Different compartments harbor different populations of lymphocytes, subpopulation of the white blood cells. One of these compartments in the spleen is the so-called marginal zone. Most of the cells that are located in this compartment are a special subpopulation of B-lymphocytes, the marginal zone B-lymphocytes. These cells have unique properties, and seem to play a critical role in the responses to micro-organisms in the blood. Like other B-lymphocytes, marginal zone B-lymphocytes recognize micro-organisms with special receptors on their surface, the immunoglobulins (also called antibodies). After binding to micro-organisms, activated B-lymphocytes secrete immunoglobulins in large quantities to inactivate the micro-organisms. In this thesis we studied the type of B-lymphocytes in the marginal zone of the rat. To this end we first analyzed the organization of immunoglobulin genes in the DNA. This information was subsequently used to study the nature and origin of B-lymphocytes in the marginal zone. We found that most cells are naïve B-lymphocytes, i.e. lymphocytes that never had encountered micro-organisms, whereas a minor fraction of these cells represent memory B-lymphocytes. These cells have been formed during a previous contact with micro-organisms. This is reflected by mutations in the genes that encode for the immunoglobulins. Memory B-lymphocytes are generally thought to be derived from the special structures present in the lymphoid organs, the germinal centers. Here we provide evidence that also memory B-lymphocytes in the marginal zone are also derived from these structures.