Haruo Nagumo

CD27: a memory B-cell marker

Abstract Memory B cells generate immunoglobulins rapidly and vigorously in the secondary immune response. Here, Kazunaga Agematsu and colleagues highlight studies confirming that CD27 is a memory B-cell marker.

Absence of IgD-CD27(+) memory B cell population in X-linked hyper-IgM syndrome.

The present study analyzed peripheral blood B cell populations separated by IgD and CD27 expression in six males with X-linked hyper-IgM syndrome (XHIM). Costimulation of mononuclear cells from most of the patients induced no to low levels of class switching from IgM to IgG and IgA with Staphylococcus aureus Cowan strain (SAC) plus IL-2 or anti-CD40 mAb (anti-CD40) plus IL-10. Measurable levels of IgE were secreted in some of the patients after stimulation with anti-CD40 plus IL-4. Costimulation with SAC plus IL-2 plus anti-CD40 plus IL-10 yielded secretion of significant levels of IgG in addition to IgM, but not IgA. The most striking finding was that peripheral blood B cells from all of the six patients were composed of only IgD+ CD27(-) and IgD+ CD27(+) B cells; IgD- CD27(+) memory B cells were greatly decreased. IgD+ CD27(+) B cells from an XHIM patient produced IgM predominantly. Our data indicate that the low response of IgG production in XHIM patients is due to reduced numbers of IgD- CD27(+) memory B cells. However, the IgG production can be induced by stimulation of immunoglobulin receptors and CD40 in cooperation with such cytokines as IL-2 and IL-10 in vitro.

Theophylline induces neutrophil apoptosis through adenosine A2A receptor antagonism.

This study was designed to determine whether theophylline would augment granulocyte apoptosis via a mechanism of adenosine A2A receptor antagonism. A selective adenosine A2 receptor agonist (CGS‐21680, 1 μM) exhibited the most efficient potency for decreasing neutrophil apoptosis for 16 h from 63 ± 5 to 19 ± 4% (P < 0.001); it exerted poor and adverse effects on eosinophil survival. A selective protein kinase A inhibitor KT‐5720 (10 μM) reversed the capacity of dibu‐tyryl cAMP but not CGS‐21680 to induce an inhibitory effect on neutrophil apoptosis, suggesting that occupancy of adenosine A2 receptors inhibit neutrophil apoptosis by a cAMP‐independent mechanism. Theophylline derivatives show the following pattern of potency for inducing neutrophil apoptosis competing with CGS‐21680: 8‐phenyltheophylline = 8‐p‐sulfophenyltheophylline > theophylline ≫ enprofylline. This pattern is consistent with the affinity established for A2A receptors. Theophylline demonstrated an additive effect to that of anti‐Fas antibody (CH11, 1 μg/mL) in inducing neutrophil apoptosis, but not to that of adenosine deaminase or KF‐17837 (a selective A2 receptor antagonist; 1 μM), suggesting conflicting effects on the receptor antagonism. These findings suggest that theophylline has an immunomodulatory action on neutrophil apoptosis via a mechanism of A2A antagonism. J. Leukoc. Biol. 67:529–535; 2000.

Plasma Cell Generation from B-Lymphocytes via CD27/CD70 Interaction

To produce antibodies, the differentiation of B cells into antibody-secreting cells, plasma cells, is required. We describe that ligation of CD27, which belongs to the tumor necrosis factor receptor (TNFR) family and is a memory marker of B cells, yields crucial signals that positively control the entry of B cells into the pathway to plasma cells. The triggering via CD27 by CD27 ligand (CD70) on purified peripheral blood B cells yielded an increase in the number of plasma cells in the presence of interleukin-10 (IL-10). The differentiation into plasma cells by a combination of IL-10 and CD70-transfectants occurred in CD27+ B cells, but not in CD27- B cells. Moreover, the addition of IL-2 to the IL-10 and CD70-transfectants greatly induced the differentiation into plasma cells. In the presence of only IL-2, IL-4 or IL-6, CD70-transfectants did not promote the differentiation into plasma cells. On the other hand, CD40 signaling increased the expansion of a B cell pool from peripheral blood B cells primarily activated by IL-2, IL-10 and anti-CD40 mAb. These data demonstrate that CD27 ligand (CD70) is a key molecule to direct the differentiation of CD27+ memory B cells toward plasma cells in cooperation with IL-10.

Synergistic augmentative effect of interleukin-10 and CD27/CD70 interactions on B-cell immunoglobulin synthesis.

Interleukin‐10 (IL‐10) is a potent cytokine that regulates immunoglobulin synthesis by B cells. CD27/CD70 interactions by direct cell‐to‐cell contact are also needed to produce substantial amounts of immunoglobulin. We have investigated the effects of IL‐10 and CD27/CD70 interactions on the immunoglobulin synthesis. In the presence of IL‐10 stimulation, the production of IgG, IgM and IgA was increased synergistically by the addition of CD27 ligand (CD70)‐transfectants in a dose‐dependent manner, which was completely blocked by anti‐CD70 monoclonal antibody. In contrast, CD70‐transfectants additively enhanced the immunoglobulin production in the presence of IL‐2, IL‐4, or IL‐6. The synergistic enhancement of the immunoglobulin production by IL‐10 and CD70‐transfectants was remarkable in highly purified CD27+ B cells, but there was no immunoglobulin production in CD27− B cells. Furthermore, by the addition of CD70‐transfectants, the synthesis of IgG1, IgG2, IgG3 and IgG4 was also enhanced in the presence of IL‐10. On the other hand, IL‐10 diminished CD27 expression in B cells. B‐cell proliferation was augmented by CD70‐transfectants with IL‐10 or IL‐10 plus IL‐2. The addition of IL‐2 further augmented the immunoglobulin production which was synergistically enhanced by IL‐10 and CD27 triggering. Taken together, the co‐operative response to IL‐10 and CD27/CD70 interactions regulates B‐cell immunoglobulin production.

IL-10 enhances B-cell IgE synthesis by promoting differentiation into plasma cells, a process that is inhibited by CD27/CD70 interaction

Interleukin‐10 (IL‐10) is a major regulatory cytokine of inflammatory responses that is considered to play an important role in specific immunotherapy. However, whether IL‐10 enhances or inhibits B‐cell IgE production has remained a matter of contention. To clarify the effect of IL‐10 on IgE synthesis in the presence of IL‐4 and CD40 signalling, we examined B‐cell proliferation, germline ɛ transcripts and plasma cell differentiation. In addition, the effect of CD27 signalling on IgE synthesis in the presence of IL‐10, IL‐4 and CD40 signalling was investigated. IL‐10 facilitated the production of IgE in mononuclear cells and highly purified B‐cells, enhanced B‐cell proliferation and, most importantly, promoted the generation of plasma cells. However, IL‐10 did not enhance expression of germline ɛ transcripts. The addition of CD27 signalling through the use of CD32–CD27 ligand (CD70) double transfectants significantly diminished the B‐cell proliferation, IgE synthesis and plasma cell differentiation enhanced by IL‐10. IL‐10 enhances B‐cell IgE production by promoting differentiation into plasma cells. CD27/CD70 interactions under IL‐10 and sufficient CD40 cosignalling exert the opposite effect on IgE synthesis. The results of this study indicate that precautions are critical when planning immunotherapy using IL‐10 in IgE‐related allergic diseases.

Granulocyte macrophage-colony stimulating factor delays neutrophil apoptosis and primes its function through Ia-type phosphoinositide 3-kinase

Phosphoinositide 3‐kinases (PI3Ks) constitute a family of lipid kinases that regulate an array of fundamental cellular responses by neutrophils [polymorphonuclear leukocytes (PMN)]. p85α Gene‐disrupted mice were used to help accurately identify the physiological role of the PI3K isoform in PMN activation in the presence of granulocyte macrophage‐colony stimulating factor (GM‐CSF). PMN from the p85α−/− mice showed normal cellular motility, and the quantity of superoxide anion () produced by PMN upon stimulation with formyl‐Met‐Leu‐Phe did not significantly differ between p85α−/− and wild‐type mice under controlled conditions. In p85α−/− mice, the production by PMN was enhanced (primed) by GM‐CSF when stimulated with the chemotactic peptide but to a significantly lesser extent than in wild‐type mice. In addition, no major GM‐CSF‐dependent delay in apoptosis or activation of Akt protein phosphorylation by GM‐CSF was observed in the p85α−/− mice. In terms of targeting strategy, however, the mutation actually expressed a small amount of Ia‐type (p85α‐regulated) PI3K activity (partially abrogated) in the mice. These results demonstrate that Ia‐type PI3K plays a critical role in the enhancement of the GM‐CSF‐modulated function of PMN and in the PI3K/Akt pathway‐dependent delay of PMN apoptosis.

CD72-mediated suppression of human naive B cell differentiation by down-regulating X-box bindingprotein 1

B cells can differentiate into antibody‐secreting plasma cells, however the signals that control the entry into this pathway are not clearly understood. We have investigated the role of human CD72 in mature B cell differentiation. Human CD72 is preferentially expressed in naive B cells, but marginal levels of expression can be found in switched memory B cells. CD72 cross‐linking promoted an increase in B cell activation and proliferation. Interestingly, expression of CD27, whose signal induces the differentiation of B cells into plasma cells, was down‐modulated by CD72 stimulation. This CD72 signaling also induced tyrosine phosphorylation of various proteins such as Blk. Plasma cell differentiation and Ig syntheses were diminished by CD72 ligation in the presence of Staphylococcus aureus Cowan strain (SAC) plus IL‐2 but not in the presence of CD40 signaling or CpG oligodeoxynucleotide. Our results show that CD72 signaling reduces the expression of X‐box binding protein 1 in B cells stimulated with SAC plus IL‐2, but the expression of PRDI‐BF1 was unaffected. Taken together, these data demonstrate that CD72 is a key molecule in regulating mature B cell differentiation, particularly in preventing the differentiation of naive B cells into plasma cells, thus blocking the production of low‐affinity antibodies.

Expansion of clonotype-restricted HLA-identical maternal CD4+ T cells in a patient with severe combined immunodeficiency and a homozygous mutation in the Artemis gene.

We have observed a male infant with severe combined immunodeficiency (SCID) responsible for Artemis gene mutation, in whom marked expansion of the transplacentally grafted maternal CD4(+) T cells was observed in various tissues. His class I and II major histocompatibility antigens (MHC) were identical to his mothers. We analyzed the T-cell populations within target tissues at a molecular level in order to determine whether different T-cell clonotypes are expanded in different types of tissue. Prior to T-cell expansion, the T-cell receptor variable beta (TCRBV) 5.1 subfamily predominated in peripheral blood (PB) lymphocytes. Third complementarity determining region (CDR3) size spectratyping and amino acid sequencing showed that the range of T-cell clonotypes was very restricted. After T-cell expansion, different TCRBV subfamilies were found to predominate in different target tissues; these included TCRBV 5.1 and 17 in the PB, TCRBV 13 and 21.3 in the bone marrow, and TCRBV 17 in lymph nodes. CDR3 size analysis showed that the expression of different proliferating T-cell clonotypes remained restricted after T-cell expansion. These results indicate that highly restricted maternal T-cell clonotypes can markedly expand, possibly in response to tissue-specific antigens, in a MHC-identical recipient.

Distinct response in maintenance of human naive and memory B cells via IL-21 receptor and TCL1/Akt pathways.

The molecular mechanisms involving in B-cell survival/proliferation are poorly understood. Here we investigated the molecules affecting the survival of human naïve and memory B cells. Without stimulation, naïve B cells survived longer than memory B cells. Moreover, the viability of memory B cells decreased more rapidly than that of naïve B cells following with Staphylococcus aureus Cowan strain (SAC), anti-immunoglobulin (Ig), or anti-CD40 stimulation, but displayed the same levels of survival following CpG DNA stimulation. We analyzed the transcriptional differences between B-cell subsets by gene expression profiling, and identified 15 genes significantly correlated to survival/proliferation. Among them, IL-21 receptor (IL-21R) and T-cell leukemia 1 (TCL1) proto-oncogene were highly expressed in naïve B cells. IL-21 induced the proliferation of both naïve and memory B cells. Marked phosphorylation of Akt was found in naïve B cells compared with memory B cells. This study suggests that naive and memory B cells are regulated by several distinct molecules, and the IL-21R and TCL1/Akt pathways might play crucial roles in naïve B cells for their maintenance.