Germinal center-associated nuclear protein contributes to affinity maturation of B cell antigen receptor in T cell-dependent responses

doi:10.1073/pnas.0307609100

Germinal center-associated nuclear protein contributes to affinity maturation of B cell antigen receptor in T cell-dependent responses

^*Department of Immunology, Graduate School of Medical Sciences, Kumamoto University, Honjo, Kumamoto 860-8556, Japan; ^‡Department of Immunology, National Institute of Infectious Diseases, Toyama, Shinjuku-ku, Tokyo 162-8640, Japan; ^§Division of Reproductive Engineering, Center for Animal Resources and Development, Kumamoto University, Honjo, Kumamoto 860-0811, Japan; ^¶Laboratory for Vertebrate Body Plan, RIKEN Center for Developmental Biology, Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan; and ^†PRESTO and ^∥CREST, Japan Science and Technology Agency, Honcho, Kawaguchi City, Saitama Pref. 332-0012, Japan

Communicated by Tadamitsu Kishimoto, Osaka University Medical School, Osaka, Japan, November 18, 2003 (received for review August 29, 2003)

Abstract

Acquired immunity depends on proliferation and differentiation of antigen (Ag)-specific B cells in germinal centers (GCs) of lymphoid follicles in response to T cell-dependent Ags. Here, we studied the function of GC-associated nuclear protein that is selectively up-regulated in GC-B cells. B cell-specific ganp-deficient mice were compromised in affinity maturation of hapten-specific antibodies against T cell-dependent Ags with retarded development of GCs. B cell numbers and development, serum Ig levels, mitogen-induced B cell proliferation in vitro, and responses to T cell-independent Ag were nearly normal; however, the mutant B cells showed a decrease in anti-CD40-induced proliferation and an increased susceptibility to B cell apoptosis in vitro and in vivo. B cell-specific ganp-deficient mice showed a decreased frequency of variable-region somatic mutations, especially of the high-affinity type (W³³ → L) in the V_H186.2 region against nitrophenyl-chicken gamma globulin, whereas the class switching was normal. We conclude that GC-associated nuclear protein is necessary for generation or maintenance of B cells with high-affinity B cell Ag receptors during the maturation in GCs.

Footnotes

↵ ** To whom correspondence should be addressed. E-mail: nobusaka{at}kaiju.medic.kumamoto-u.ac.jp.
Abbreviations: Ag, antigen; BCR, B cell antigen receptor; CSR, class switch recombination; NP, nitrophenyl; NP-CG, NP-chicken gamma globulin; PNA, peanut agglutinin; SHM, somatic hypermutation; TD-Ag, T cell-dependent antigen; TNP-KLH, trinitrophenyl-keyhole limpet hemocyanin; V region, variable region; AICD, activation-induced cell death; GC, germinal center; GANP, GC-associated nuclear protein; LPS, lipopolysaccharide; TUNEL, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling.