530 PARt IV The Immune System in Health and Disease heterokaryons, containing nuclei from both parent cells. Ran Chromosomes dom loss of some chromosomes and subsequent cell prolifer ation yield a clone( contain a single nucleus with chromosomes fro of the fused cells such a clone is called a hybridoma. Historically, cell fusion was promoted with Sendai virus, but now it is generally done with polyethylene glycol. Normal antigen-primed B cells can be fused with cancerous plasm Normal t or B cell ancerous t or b cell cells, called myeloma cells( Figure 23-2). The hybridoma 7-10 (grows continuously thus formed continues to express the antibody genes of the normal B lymphocyte but is capable of unlimited growth, a characteristic of the myeloma cell. B-cell hybridomas that secrete antibody with a single antigenic specificity, called monoclonal antibody, in reference to its derivation from a single clone, have revolutionized not only immunology but biomedical research as well as the clinical laboratory. Chapter 4 describes the production and uses of monoclonal antibod- ies in detail (see Figures 4-21) Nucleus Nucleus of of normal T-cell hybridomas can also be obtained by fusing T lym- lymphocyte phocytes with cancerous T-cell lymphomas. Again, the result ing hybridoma continues to express the genes of the normal Tcell but acquires the immortal-growth properties of the can- cerous T lymphoma cell. Immunologists have generated a Heterokaryon number of stable hybridoma cell lines representing T-helper and T-cytotoxic lineages Random chromosomal loss Protein Biochemistry The structures and functions of many important molecules of the immune system have been determined with the tech- niques of protein biochemistry, and many of these tech- niques are in constant service in experimental immunology For example, fluorescent and radioactive labels allow immu nologists to localize and visualize molecular activities, and the ability to determine such biochemical characteristics of a (expresses some normal protein as its size, shape, and three-dimensional struct grows indefinitely like a cancer cell) provided essential information for understanding the tions of immunologically important molecules. Radiolabeling Techniques Allow Sensitive detection of antio Monoclonal or Antibodies antibody 2(12) Radioactive labels on antigen or antibody are extremely sen sitive markers for detection and quantification. There are a number of ways to introduce radioactive isotopes into pro- B- teins or peptides. For example, tyrosine residues may be labeled with radioiodine by chemical or enzymatic proce dures. These reactions attach an iodine atom to the phenol FIGURE 23-2 Production of B-cell and T-cell hybridomas by ring of the tyrosine molecule. One of the enzymatic iodin- somatic-cell hybridization. The resulting hybridomas express some tion techniques, which uses lactoperoxidase, can label pro- of the genes of the original normal B or T cell but also exhibit the teins on the plasma membrane of a live cell without labeling immortal-growth properties of the tumor cell. This procedure is used proteins in the cytoplasm, allowing the study of cell-surface to produce B-cell hybridomas that secrete monoclonal antibody and roteins without isolating them from other cell constituents. T-cell hybridomas that secrete various growth factors.heterokaryons, containing nuclei from both parent cells. Ran￾dom loss of some chromosomes and subsequent cell prolifer￾ation yield a clone of cells that contain a single nucleus with chromosomes from each of the fused cells; such a clone is called a hybridoma. Historically, cell fusion was promoted with Sendai virus, but now it is generally done with polyethylene glycol. Normal antigen-primed B cells can be fused with cancerous plasma cells, called myeloma cells (Figure 23-2). The hybridoma thus formed continues to express the antibody genes of the normal B lymphocyte but is capable of unlimited growth, a characteristic of the myeloma cell. B-cell hybridomas that secrete antibody with a single antigenic specificity, called monoclonal antibody, in reference to its derivation from a single clone, have revolutionized not only immunology but biomedical research as well as the clinical laboratory. Chapter 4 describes the production and uses of monoclonal antibod￾ies in detail (see Figures 4-21). T-cell hybridomas can also be obtained by fusing T lym￾phocytes with cancerous T-cell lymphomas. Again, the result￾ing hybridoma continues to express the genes of the normal T cell but acquires the immortal-growth properties of the can￾cerous T lymphoma cell. Immunologists have generated a number of stable hybridoma cell lines representing T-helper and T-cytotoxic lineages. Protein Biochemistry The structures and functions of many important molecules of the immune system have been determined with the tech￾niques of protein biochemistry, and many of these tech￾niques are in constant service in experimental immunology. For example, fluorescent and radioactive labels allow immu￾nologists to localize and visualize molecular activities, and the ability to determine such biochemical characteristics of a protein as its size, shape, and three-dimensional structure has provided essential information for understanding the func￾tions of immunologically important molecules. Radiolabeling Techniques Allow Sensitive Detection of Antigens or Antibodies Radioactive labels on antigen or antibody are extremely sen￾sitive markers for detection and quantification. There are a number of ways to introduce radioactive isotopes into pro￾teins or peptides. For example, tyrosine residues may be labeled with radioiodine by chemical or enzymatic proce￾dures. These reactions attach an iodine atom to the phenol ring of the tyrosine molecule. One of the enzymatic iodina￾tion techniques, which uses lactoperoxidase, can label pro￾teins on the plasma membrane of a live cell without labeling proteins in the cytoplasm, allowing the study of cell-surface proteins without isolating them from other cell constituents. 530 PART IV The Immune System in Health and Disease Polyethylene glycol Chromosomes Normal T or B cell (dies after 7–10 days in culture) Cancerous T or B cell (grows continuously in culture) Heterokaryon Nucleus of cancer cell Nucleus of normal lymphocyte Random chromosomal loss Hybridoma (expresses some normal B-cell or T-cell genes but grows indefinitely like a cancer cell) B-cell hybridoma T-cell hybridoma Monoclonal antibody Interleukin 2 (IL-2) FIGURE 23-2 Production of B-cell and T-cell hybridomas by somatic-cell hybridization. The resulting hybridomas express some of the genes of the original normal B or T cell but also exhibit the immortal-growth properties of the tumor cell. This procedure is used to produce B-cell hybridomas that secrete monoclonal antibody and T-cell hybridomas that secrete various growth factors