Toshimasa Nakagawa

B Cell Growth and Differentiation Factors and Mechanism of B Cell Activation

B cells, one of the best understood eukariotic cells, originate from pluripotent hematopoietic stem cells and differentiate into immunoglobulin {Ig)-secreting cells through multistep developmental stages, such as pre-pre-B cells, pre-B cells, immature B cells, mature B cells, activated B cells and Ig-secreting cells. An understanding of the stimuli which cause the activation, proliferation and differentiation of B cells is critical to the delineation of the normal regulation of the immune responses as well as proliferation and differentiation of eukariotic cells. Since the discovery of T-B collaboration in the antibody response, extensive studies on the regulatory molecules involved in B cell activation have been done. More than a decade ago, Dutton and his colleagues (1971) suggested the involvement of soluble helper factors in the T cell-dependent activation of B cells into Ig-secreting cells. Since then, hundreds of factors, antigen specific or nonspecific, have been reported and those results have supported the notion that helper or suppressor function of T cells in B cell activation can be replaced by the soluble products released from T cells. Kishimoto and Ishizaka (1975) and Kishimoto and his colleagues (1975) have shown Ig-induction in rabbit B cells by anti-Ig and T cell-derived helper factors, suggesting that 2 signals, crosslinkage of Ig-receptors and helper factors, could induce activation of B cells into Igproducing cells. This finding was confirmed by several investigators in murine or human B cells (Parker etal. 1979, Isakson etal. 1981, Yoshizaki et al. 1982)and also supported the notion that helper function of T cells was mediated by T cellderived helper factors.

Emergence of an Influenza B Virus with Antigenic Change

ABSTRACT Influenza B virus Yamagata group strains, isolated in the 2000 to 2001 influenza epidemic season, reacted poorly to the polyclonal ferret sera prepared against strains isolated earlier. The results of genetic analysis clarified that a point mutation of the nucleotide at position 126 in the HA1 region and the corresponding one-amino-acid substitution altered viral antigenicity.

Cocirculation of Antigenic Variants and the Vaccine-Type Virus during the 2004-2005 Influenza B Virus Epidemics in Japan

ABSTRACT In the 2004-2005 season, there was a large epidemic of the influenza B virus Yamagata group in Kobe, Japan. In hemagglutination inhibition tests, most of the clinical isolates from Kobe showed antigenicities similar to those of previous isolates (the vaccine-type virus). Only a few antigenic variants were isolated around the peak of the epidemic; however, Kobe residents developed antibodies against the variants during the season. The antigenic variants showed a one-point mutation of a nucleotide in the HA1 gene (C440A or G421A), which resulted in the substitution of one amino acid in the 150 loop of the HA molecule (T147N or G141R). The 150 loop is one of four epitopes of the hemagglutinin molecule of the influenza B virus. We established a system to detect one-point differences in the nucleotides of the 150 loop by means of high-resolution melting curve analysis with LCGreen. With this system, the isolates were determined to be the vaccine-type virus, antigenic variants, or a mixture of both. Some isolates were shown to be mixtures although they had been recognized as the vaccine-type virus with the hemagglutination inhibition tests. Thus, the antigenic variants appeared in the early period of the epidemic and were cocirculating with the vaccine-type virus during the epidemic.

The Activation, Proliferation, and Differentiation of Human B Lymphocytes

Efforts to evaluate normal human B cell physiology have resulted in the development of a model in which a resting B cell must progress through stages of activation, proliferation, and differentiation before becoming an immunoglobulin (Ig)-producing cell (1–4). Presumably each of these stages has specific signals, positive as well as negative, which control the nature as well as the intensity of the response. To evaluate the validity of this model, researchers have looked for reagents which act selectively at each of these stages. These include antigens, mitogens, soluble factors produced by various cell types, and various pharmacologic agents. In this review we will emphasize some of the studies performed in our laboratory on the various stages of B cell function in humans.

ACTIVATION OF HUMAN MONOCLONAL B CELLS WITH ANTI-Ig AND T CELL-DERIVED HELPER FACTOR(S) AND BIOCHEMICAL ANALYSIS OF THE TRANSMEMBRANE SIGNALING IN B CELLS

ABSTRACT Ig production was induced in human leukemic B cells or a transformed B cell line (CESS) by anti-Ig or T cell-derived helper factor(s). It was shown that three signals, i.e., crosslinkage of Ig receptors by anti-Ig, B cell growth factor (BCGF) and T cell replacing factor (TRF), were required for the activation of leukemic B cells into Ig-producing cells. Establishment of human T hybridomas secreting monoclonal immunoregulatory molecules showed that BCGF or TRF was different from the factor required for the proliferation of T cells (IL-2). Injection of the cytoplasm from TRF-stimulated CESS cells into non-stimulated cells induced IgG production, suggesting TRF-induced generation of the cytoplasmic sub-stnace responsible for the signal transmission. The binding of TRF with TRF acceptors induced methylation of membrane phospholipids followed by the activation of serine esterase. TRF-activated serine esterase was shown to be involved in the generation of the cytoplasmic factor(s) which were responsible for the signal transmission from membrane to nuclei.

The Effects of Interleukin 2, Gamma Interferon, and B Cell Differentiation Factor on the Differentiation of Human B Cells

It has been well known that in the human system, SAC-activated B cells proliferate and differentiate in response to helper T cell factors. Among many factors included within the broad category of helper T cell factors, three distinct factors (interleukin 2 IL-2, gamma interferon γ-IFN, and B cell differentiation factor BCDF) were reported to be involved in B cell differentiation. Recent progress in recombinant DNA technology has made highly purified IL-2 and γ-IFN available, and even though BCDF is not yet cloned by molecular biological techniques, two kinds of BCDFs derived from the supernatants of newly established cell lines have been recently reported. In the present study, employing normal B cells or EBV-transformed B cell lines, we have investigated the effects of these factors on human B cells.

Regulation of human B lymphocytes differentiation: Characterization of B cell stimulatory factors

B lymphocytes originate from pluripotent hematopoietic stem cells and differentiate into antibody producing cells through several distinct differentiation stages. Commitment of the antigen specificity in each B cell clone occurs at the stage of pre B cells by two step DNA rearrangements including V, D and J segments, i.e. from DJ joining to the functional VDJ formation (1). Following the rearrangement of heavy chain genes, light chain gene rearrangements occur (2) and 7S IgM molecules are expressed as antigen receptors on the surface of mature B cells. A given antigen selects a B cell clone with a matched receptor and activates this clone into antibody producing cells under the influence of helper T cells.