Kazunaga Agematsu

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.

Inhibition of Methicillin-Resistant Staphylococcus aureus Colonization of Oral Cavities in Newborns by Viridans Group Streptococci

We investigated the role of viridans group streptococci in the prevention of colonization with methicillin-resistant Staphylococcus aureus (MRSA) in neonatal intensive care units. During a 26-month period at a childrens hospital, 207 (49.9%) of 415 newborns were colonized with MRSA by the time of discharge. Two groups of newborns with matching durations of hospitalization were compared with regard to the prevalence of future colonization with MRSA: group 1 (103 patients) did not acquire colonization with viridans group streptococci and group 2 (63 patients) did acquire colonization with viridans group streptococci at birth or by 1 to 2 weeks (age, < or =11 days). The rate of colonization among patients in group 2 (9.5%) was significantly lower than that among patients in group 1 (44.7%; P<.001). No significant difference in patient characteristics (e.g., birth weight, diseases) was observed. These results indicate that viridans group streptococci, as bacteria that formerly occupied the oral cavities in newborns, may inhibit later colonization with MRSA.

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.

Direct B/B–cell interactions in immunoglobulin synthesis

The principal roles of B/B‐cell interactions in immune response have not yet been established. We therefore investigated B/B‐cell interactions in immunoglobulin synthesis via direct cell‐to‐cell contact, particularly in the tumour necrosis factor receptor (TNFR)/tumour necrosis factor (TNF) family. We prepared highly purified peripheral blood B cells and stimulated them with Epstein–Barr virus (EBV)‐transformed B lymphoblastoid cell lines (LCLs) as activated human B cells. The IgG production by B cells was increased by the addition of fixed LCLs in a dose‐dependent manner in the presence of IL‐10 plus IL‐2. LCLs strongly expressed CD40 and CD70 on their surface, but marginal or no CD154, CD27, OX40 (CD134) and CD134 ligand. The enhancement of immunoglobulin production by LCLs was completely blocked by the initial addition of anti‐CD70 blocking MoAb, but not by anti‐CD154 or anti‐CD134 ligand MoAb. The addition of LCLs also caused a reduction in CD27 expression on B cells, and this effect was completely blocked by anti‐CD70 MoAb, indicating a direct B cell–LCL contact via CD27/CD70. LCLs markedly promoted B‐cell differentiation into plasma cells in the presence of IL‐10 plus IL‐2. These findings demonstrate that direct interactions between B and B cells via CD27/CD70 induce immunoglobulin production by promoting the generation of plasma cells.

Presenility of granulocytes in Down syndrome individuals

Neutrophil function defects occur in individuals with Down syndrome (DS). We examined apoptosis of granulocytes (neutrophils and eosinophils) in DS individuals and control healthy subjects. Granulocyte survival was shortened in DS individuals, and the percentage of apoptotic granulocytes from DS during incubation was significantly higher than that from healthy subjects. The difference was time-dependent, and that between DS and healthy subjects was nearly 30% after longer periods of incubation. In control granulocytes, both granulocyte-macrophage colony-stimulating factor (10 ng/ml) and interleukin-5 (5 ng/ml) counteracted the programmed cell death and delayed the apoptosis caused by anti-Fas antibodies, whereas those inflammatory cytokines were not able to completely prevent cellular apoptosis in DS patients. Apoptosis and functional impairment of granulocytes may contribute to the risk of infections underlying pathological conditions of DS, and accelerated apoptosis of granulocytes may be a factor to prevent chronic airway inflammation and bronchial asthma in DS individuals.

A thiol proteinase inhibitor, E-64-d, corrects the abnormalities in concanavalin A cap formation and the lysosomal enzyme activity in leucocytes from patients with Chediak-Higashi syndrome by reversing the down-regulated protein kinase C activity

We have reported previously that the abnormally down‐regulated protein kinase C (PKC) causes cellular dysfunction observed in natural killer (NK) cells, polymorphonuclear leucocytes (PMNs) and fibroblasts from beige mouse, an animal model of Chediak–Higashi syndrome (CHS). Here we show that the abnormal down‐regulation of PKC activity also occurs in Epstein–Barr (EB) virus‐transformed cell lines from CHS patients. When CHS cell lines were stimulated with concanavalin A (Con A) for 20 min, the membrane‐bound PKC activity declined markedly, whereas that in control cell lines increased. We found that E‐64‐d, which protects PKC from calpain‐mediated proteolysis, reversed the declined PKC activity and corrected the increased Con A cap formation to almost normal levels in CHS cell lines. We confirmed that the dysregulation of PKC activity also occurred in peripheral blood mononuclear leucocytes (PBMC) from CHS patients and that E‐64‐d corrected both the declined PKC activity and increased Con A cap formation. E‐64‐d also corrected the reduced lysosomal elastase and cathepsin G activity in CHS cell lines. In contrast, chelerythrin, a specific inhibitor of PKC, and C2‐ceramide, which promotes PKC breakdown induced by calpain, increased Con A cap formation and inhibited both elastase and cathepsin G activity in normal cell lines. Moreover, we found that ceramide production in CHS cell lines increased significantly after Con A stimulation, which coincides with our previous observation in fibroblasts from CHS mice. These results suggest an association between ceramide‐induced PKC down‐regulation and the cellular dysfunctions in CHS.

Complete arrest from pro‐ to pre‐B cells in a case of B cell‐negative severe combined immunodeficiency (SCID) without recombinase activating gene (RAG) mutations

The B‐cell lineage in a patient with B‐cell‐negative severe combined immunodeficiency (SCID) was analysed by using antisurrogate light chain (SL) MoAbs. Peripheral CD3+ T cells and CD19+ B cells were absent in the patient. The common gamma (γc) chain was expressed normally on the patients peripheral NK cells and his peripheral mononuclear cells did not possess any mutations in recombinase activating gene (RAG)‐1, 2. Normal levels of expression of Ku70 and Ku80 protein were found by Western blot analysis. The patient did, however, display an increase in fibroblast sensitivity to irradiation. Furthermore, flow cytometric analyses of bone marrow cells showed that surface IgM and cytoplasmic µ positive cells were absent and that CD19+ B cells were composed of only CD34+ terminal deoxynucleotidyl transferase (TdT)+ SL+ pro‐B cells. The complete arrest of pro‐ to pre‐B cell development in the SCID patients bone marrow suggests that some genes involved in V(D)J recombination, excepting the RAG gene, may play a causative role in the immunodeficiency.