The realization of essential cellular'interactions in the immune response convokes a better understandin~ of the fixed and free cellular components of lymphatic tissue. Ger~inal centers of lymphatic tissue have long been considered to have a funda~ental role in the immune reaction, and have been suspected of being topographic regions where so~e of these essential cellular inter­ actions may occur. The physiological significance of these topo­ graphic regions in lynphatic tissue is only now becoming clarified from recent studies of antigen localization, but the histo2enic relation of the cellular compartments still needs to be resolved. This book represents the Proceedings of the Second International Conference on Lymphatic Tissue Germinal Centers, held at the University of Padova, Padova, Italy, June 26-28, 1968. The aim of the ~eeting was to bring together current infor~ation on the physiological significance of germinal centers in ly~rhatic tissue and their possible role in the immune response. The range of interests extended from phylogenesis and ~orphology to studies of antigen and viral localization, cytokinetics and cytodifferen­ tiation, immunochemistry, and im~unosuppression. The interactions of central lymphoid organs, such as the thymus and bursa, are studies having an essential role in these Proceedings. Also, several studies deal with lymphatic tissue germinal centers in delayed hypersensitiv­ ity and neoplastic disease. The effects of immunosuppressive drugs, antilymphocyte serum, radiation and hormones on lymphatic tissue and germinal centers are also areas covered in these Proceedings.

Session 1 Development of Lymphoid Tissue and Germinal Centers in Relation to Phylogenesis.- Specific Immunoglobulin Synthesis in Lower Vertebrates Lacking Germinal Centers.- Theliolymphoid Organs - A New Look at the Lymphoepithelial Organs.- The Development of Lymphoid Systems: Immune Response and Radiation Sensitivity in Lower Vertebrates.- Studies on the Mature of Germinal Centers.- Session 2 Morphology and Functional Activity of Lymphoid Tissue and Germinal Centers.- Reticulum Arrangement Related to the Behavior of Cell Populations in the Mouse Lymph Node.- The White Pulp of the Human Spleen in Three Dimensions, and its Relation to Immunologic Function.- Cytophotometric and Autoradiographic Investigations on Germinal Center Cells in Man.- Differentiation Pathway within Germinal Centers of Human Tonsils.- Session 3 Cellular Kinetics of Lymphoreticular Tissue and Germinal Centers.- Germinal Centers and Immunological Memory.- Cytokinetic Studies on Tingible Bodies in Germinal Centers of Peyer's Patches in Mice.- Studies on the Kinetics and Radiation Sensitivity of Dendritic Macrophages.- Session 4 Origin and Migration of Lymphoid Cells.- Histophysiology of Germinal Centers and their Role in Antibody Response: An Autoradiographic Study in the Rabbit.- Mouse Blood Lymphocytic Origins Investigated by a Simple Cell Culture Technique.- Lymphatic Drainage of Thymic Lymphocytes in Mice.- Lymphoid Cell Migration and Germinal Centers.- The Mitotic Response of Thymus-derived Cells to a Variety of Different Antigens.- Session 5 Germinal Centers in Relation to Antigen Localization and Antibody Production, Part I.- The Relation of Antigen and Virus Localization to the Development and Growth of Lymphoid Germinal Centers.- Radiosensitivity of the Antigen-Trapping Mechanism and itsRelation to the Suppression of Immune Response.- The Immunologic Specificity of Ferritin Uptake by Macrophages in the Rat.- Kinetic Studies on the Induction of Immune Tolerance to Protein Antigen in Sublethally X-Irradiated Rabbits.- Immunogenicity Decay of Foreign Antigens in the Mouse.- Detection of Virus Particles in Lymphatic Tissue Germinal Centers.- Session 6 Germinal Centers in Relation to Antigen Localization and Antibody Production, Part II.- Localization by Immunofluorescence of 19S and 7S Immunoglobulin in the Lymphoid Tissue of the Chicken and its relation to Specific Antibody Production.- Histologic Localization of Hemolysin-Containing Cells.- The Morphologic Sites of Bacteriolytic Antibody Formation to E. coll Antigen in Mice.- Immune Response in Mice: A Comparison of the Secondary Immune Response and the Response Elicited with Immune Complexes.- Cellular Changes and Gamma Globulin Production in MouseJSpleen Durinq Induction of Immunoloaical Tolerance.- Session 7 Role of Central Lymphoid Organs in Germinal Center Formation.- Germinal Center Formation and Antibody Production in Chickens Grafted In Ovo with Allogeneic Thymus, Bursa, and Spleen.- Developmental Suppression of Germinal Center and IgG Production by Prednisolone and 6-Mercaptopurine.- Regional Disparity of Germinal Center Development in Neonatally Thvmectomized Mice after Stimulation with Tetanus Toxoid.- Session 8 Germinal Centers in Delayed Sensitivity.- The Source of Cells within Different Areas of Lymph Nodes Draining the Site of Primary Stimulation with a Contact Sensitizing Agent.- Cytodynamics of the Immunological Response Evoked by Allooeneic Graft and Heterologous Erythrocytes.- Further Studies on the Relation between Germinal Centers and Cell-Mediated Injury.- Germinal Centers of LymphNodes and Spleen in Grafted Rats.- Alloantibody-Forming Cells in Skin Allografted Mice Detected by Immunocytoadherence.- Session 9 Effects of Immuno-Suppressive Agents on Lymphoreticular Tissue.- Morphological Changes in Lymphoid Tissues of Mice Treated with Anti lymphocyte Sera.- Modifications in Lymphoid Organs after Administration of a Horse Antidog Antilymphoid Serum.- Effect of Anti lymphocyte Serum on Mouse Lymphoid Tissues In Vivo and In Vitro.- Chemical Inhibition of Blastic Transformation in Phytohemagglutinin-Stimulated Lymph Nodes.- Session 10 Endocrine Aspects of Germinal Center Control.- Relationship between Developmental Hormones, the Thymus, and Immunological Capacity.- Hormonal Control of Lymphoreticular Tissues in Snell-Bagg Pituitary Dwarf Mice.- Session 11 Immunological Recovery of Lymphoid Tissue Following X-Irradiation.- In Vitro Reactivation of Antibody Response in Explants of Irradiated Spleens.- Effect of Isogenic Red Blood Cells Transfusion on the Immune Response of Mouse Radiation Chimeras.- Immunologic Restoration of X-Irradiated Spleen by Repopulation with Circulatinn Lymphocytes.- Session 12 Functional Selection of Lymphoid Cell Population.- Absence of Complement Binding by Immunoglobulin Aggregates in Germinal Centers.- Clonal Compartmentation in the Antibody-Producing Lymph Node.- Interaction between Two Distinct Cell Lineages in an Immune Response.- Session 13 Germinal Centers in Human Pathology.- Ultrastructural Studies of Splenic Germinal Centers in Idiopathic Thrombocytopenic Purpura.- Lymphatic Follicles and Immunologic Cell Reaction in Human Jejunal Mucosa Obtained by Peroral Biopsy in Infectious Hepatitis.- Germinal Centers, Hassall's Corpuscles, and Epithelioid Granulation Tissue.- Session 14 Germinal Centers in NeoplasticDisease.- Immunoglobulins in Pregnancy and Malignant Trophoblastic Disease.- Thymic Germinal Centers as Foci of a Lymphoma Resembling Burkitt's Tumor.- Immunoglobulin-Producing Cells in Human Pericancerous Lymph Nodes.