8536d_ch05_105-136 8/22/02 2: 46 PM Page 110 mac46 mac46: 1256_deh: 8536d: Goldsby et al./Immuno 110 PART I Generation of B-Cell and T-Cell Response VISUALIZING CONCEPTS (a)A-chain DNA L V22 2C2人4C4 廿[[}∥[日[}3 2.01.3 191.4 1.71.3 kbkb (b) K-chain DNA 5凵… (c)He 5 一-…HTH FICURE 5-3 Organization of immunoglobulin germ-line gene segments. The distances in kilobases(kb) separating the various segments in the mouse: (a)A light chain, (b)K light chain, and (c) gene segments in mouse germ-line DNA are shown below each avy chain. The A and K light chains are encoded by V, ), and c chain diagram gene segments. The heavy chain is encoded by V, D, ), and C gene was found to encode amino acids 98 to 113; however, neither sequence a short distance upstream. Downstream from the of these gene segments carried the information to encode DH gene segments are six functional JH gene segments, fol amino acids 95 to 97. When the nucleotide sequence was de- lowed by a series of CH gene segments. Each CH gene seg- termined for a rearranged myeloma DNA and compared ment encodes the constant region of an immunoglobulin with the germ-line DNA sequence, an additional nucleotide heavy-chain isotype. The Ch gene segments consist of coding sequence was observed between the VH and JH gene seg- exons and noncoding introns. Each exon encodes a separate ments. This nucleotide sequence corresponded to amino domain of the heavy-chain constant region. A similar heavy acids 95 to 97 of the heavy chain. chain gene organization is found in the mouse From these results, Hood and his colleagues proposed that The conservation of important biological effector func- third germ-line gene segment must join with the VHand h tions of the antibody molecule is maintained by the limited gene segments to encode the entire variable region of the number of heavy-chain constant-region genes. In humans eavy chain. This gene segment, which encoded amino acids and mice, the Ch gene segments are arranged sequentially in within the third complementarity-determining region the order Cu, Ca, Cy ce Ca( see Figure 5-3c). This sequential (CDR3), was designated D for diversity, because of its contri- arrangement is no accident; it is generally related to the se- bution to the generation of antibody diversity. Tonegawa and quential expression of the immunoglobulin classes in the his colleagues located the d gene segments within mouse course of B-cell development and the initial IgM response of germ-line DNA with a cDNA probe complementary to the d a B cell to its first encounter with an antigen. region, which hybridized with a stretch of DNA lying be tween the VH and JH gene segments The heavy-chain multigene family on human chromo- Variable-Region Gene ome 14 has been shown by direct sequencing of DNA to Rearrangements contain 51 VH gene segments located upstream from a clus- ter of 27 functional DH gene segments. As with the light- The preceding sections have shown that functional genes chain genes, each VH gene segment is preceded by a leader that encode immunoglobulin light and heavy chains arewas found to encode amino acids 98 to 113; however, neither of these gene segments carried the information to encode amino acids 95 to 97. When the nucleotide sequence was de￾termined for a rearranged myeloma DNA and compared with the germ-line DNA sequence, an additional nucleotide sequence was observed between the VH and JH gene seg￾ments. This nucleotide sequence corresponded to amino acids 95 to 97 of the heavy chain. From these results, Hood and his colleagues proposed that a third germ-line gene segment must join with the VH and JH gene segments to encode the entire variable region of the heavy chain. This gene segment, which encoded amino acids within the third complementarity-determining region (CDR3), was designated D for diversity, because of its contri￾bution to the generation of antibody diversity. Tonegawa and his colleagues located the D gene segments within mouse germ-line DNA with a cDNA probe complementary to the D region, which hybridized with a stretch of DNA lying be￾tween the VH and JH gene segments. The heavy-chain multigene family on human chromo￾some 14 has been shown by direct sequencing of DNA to contain 51 VH gene segments located upstream from a clus￾ter of 27 functional DH gene segments. As with the light￾chain genes, each VH gene segment is preceded by a leader sequence a short distance upstream. Downstream from the DH gene segments are six functional JH gene segments, fol￾lowed by a series of CH gene segments. Each CH gene seg￾ment encodes the constant region of an immunoglobulin heavy-chain isotype. The CH gene segments consist of coding exons and noncoding introns. Each exon encodes a separate domain of the heavy-chain constant region. A similar heavy￾chain gene organization is found in the mouse. The conservation of important biological effector func￾tions of the antibody molecule is maintained by the limited number of heavy-chain constant-region genes. In humans and mice, the CH gene segments are arranged sequentially in the order C, C, C, C , C (see Figure 5-3c). This sequential arrangement is no accident; it is generally related to the se￾quential expression of the immunoglobulin classes in the course of B-cell development and the initial IgM response of a B cell to its first encounter with an antigen. Variable-Region Gene Rearrangements The preceding sections have shown that functional genes that encode immunoglobulin light and heavy chains are 110 PART II Generation of B-Cell and T-Cell Responses VISUALIZING CONCEPTS 5′ 3′ 1.3 kb 1.7 kb 1.4 kb 19 kb 1.3 kb 2.0 kb 1.2 kb 70 kb Vλ2 Jλ2 Cλ2 Jλ4 Cλ4 Vλ1 Jλ3 Cλ3 J L L λ1 Cλ1 ψ (a) λ-chain DNA 5′ 3′ 2.5 kb 23 kb Vκn Jκ Cκ (b) κ-chain DNA n = ∼85 ψ L V Vκ1 L κ2 L 5′ 3′ 34 kb 55 kb 4.5 kb 6.5 kb VH1 Cµ Cγ3 (c) Heavy-chain DNA n = ∼134 VHn D DH13 H1 JH1 Cδ JH4 Cγ1 Cγ2b Cγ2a Cε Cα 21 kb 15 kb 14 kb 12 kb L L FIGURE 5-3 Organization of immunoglobulin germ-line gene segments in the mouse: (a) light chain, (b) light chain, and (c) heavy chain. The and light chains are encoded by V, J, and C gene segments. The heavy chain is encoded by V, D, J, and C gene segments. The distances in kilobases (kb) separating the various gene segments in mouse germ-line DNA are shown below each chain diagram. 8536d_ch05_105-136 8/22/02 2:46 PM Page 110 mac46 mac46:1256_des:8536d:Goldsby et al. / Immunology 5e: