Germinal centres in T-cell-dependent antibody responses

For more than a century follicles have been recognized as a site of intense cell proliferation and cell death. At last the significance of this activity is beginning to emerge: antigen-driven B-cell proliferation, somatic mutation, positive and negative selection, and memory and plasma cell development all appear to take place within the follicle.

Growth factor requirements for the stimulation of germinal center B cells: evidence for an IL-2-dependent pathway of development

Germinal center (GC) B cells readily undergo apoptosis, a tendency which can be suppressed in vitro by immobilized anti-Ig; mAb to CD40 and soluble CD23 (in synergy with IL-1 alpha) also effect rescue of GC cells from programmed cell death. In the present study, the signals which stimulate rescued GC populations to DNA synthesis have been examined and compared to those established for the activation of follicular mantle (FM) B cells. On co-culture with anti-Ig, optimal responses in FM B cells can be achieved with a combination of IL-4 and CD40 antibody; these activities also provided a modest stimulus to GC cells but, for this population, anti-Ig was ineffective at augmenting the response further. Stimulations of GC B cells were enhanced, however, when performed on a support of primary fetal lung fibroblasts; a major influence of stroma was to promote, by direct cell-cell contact, the CD40-dependent survival of GC B cells. FM B cells were relatively independent of such stromal support. In marked contrast to FM cells, GC B cells were found to respond by enhanced DNA synthesis to IL-2 even when quite low concentrations of the factor were present (IC50 = 2 U/ml). Stimulation of GC cells via this pathway was augmented almost 2-fold on the inclusion of anti-Ig whereas neither fibroblasts, IL-4, nor CD40 antibody made any additional contribution to the IL-2-dependent response. The requirements found for stimulating GC cells in vitro are discussed with reference to the signals that this population may encounter in appropriate microenvironments in vivo: the variety of options apparently available could reflect changing priorities at different stages of a developing GC response.

Radiation dosimetry by automatic image analysis of dicentric chromosomes

A system for scoring dicentric chromosomes by image analysis comprised fully automatic location of mitotic cells, automatic retrieval, focus and digitization at high resolution, automatic rejection of nuclei and debris and detection and segmentation of chromosome clusters, automatic centromere location, and subsequent rapid interactive visual review of potential dicentric chromosomes to confirm positives and reject false positives. A calibration set of about 15,000 cells was used to establish the quadratic dose response for 60Co gamma-irradiation. The dose-response function parameters were established by a maximum likelihood technique, and confidence limits in the dose response and in the corresponding inverse curve, of estimated dose for observed dicentric frequency, were established by Monte Carlo techniques. The system was validated in a blind trial by analysing a test set comprising a total of about 8000 cells irradiated to 1 of 10 dose levels, and estimating the doses from the observed dicentric frequency. There was a close correspondence between the estimated and true doses. The overall sensitivity of the system in terms of the proportion of the total population of dicentrics present in the cells analysed that were detected by the system was measured to be about 40%. This implies that about 2.5 times more cells must be analysed by machine than by visual analysis. Taking this factor into account, the measured review time and false positive rates imply that analysis by the system of sufficient cells to provide the equivalent of a visual analysis of 500 cells would require about 1 h for operator review.

Organization of voluntary movement

There have recently been a number of advances in our knowledge of the organization of complex, multi-joint movements. Promising starts have been made in our understanding of how the motor system translates information about the location of external targets into motor commands encoded in a body-based coordinate system. Two simplifying strategies for trajectory control that are discussed are parallel specification of response features and the programming of equilibrium trajectories. New insights have also been gained into how neural systems process sensory information to plan and assist with task performance. A number of recent papers emphasize the feedforward use of sensory input, which is mediated through models of the external world, the body's physical plant, and the task structure. These models exert their influence at both reflex and higher levels and permit the preparation of predictive default parameters of trajectories as well as strategies for resolving task demands.

Money madness. Are private psychiatric hospitals resorting to kidnapping in their quest for paying patients?

In their zeal for lucrative insurance reimbursement, some private psychiatric hospitals seem to have gone over the edge themselves. A number of these institutions, critics charge, use outright coercion to commit and retain patients. Now some formerly abducted "recruits" are fighting back with lawsuits.

Germinal center cells express bcl-2 protein after activation by signals which prevent their entry into apoptosis

B cells undergo selection within germinal centers on the basis of their capacity to be activated by antigen held on follicular dendritic cells. Isolated germinal center B cells in culture kill themselves by apoptosis but this is prevented if their receptors for antigen are cross-linked. In this study it is confirmed that almost all germinal center B cells, unlike other B cells, do not express the 25-kDa protein encoded by the bcl-2 oncogene. Cross-linking the surface Ig of isolated germinal center cells causes them to express bcl-2 protein. Two other stimuli which inhibit the entry of germinal center cells to apoptosis result in the expression of bcl-2 protein. These stimuli are: (a) CD40 antibody and (b) recombinant 25-kDa fragment of the CD23 protein plus recombinant interleukin 1 alpha. Respectively, these induce germinal center cells to differentiate to resting B cells or plasmablasts. Dual-fluorescence studies on small lymphocytes confirm the presence of bcl-2 protein in mitochondria but show that this is also present in other extra-nuclear areas. Burkitt lymphoma cells have a phenotype which indicates that they are neoplastic cells of germinal center origin. The expression of bcl-2 protein by Burkitt lymphoma lines was also studied. Burkitt lines which retain the phenotype of fresh Burkitt lymphoma cells can be induced to enter apoptosis on culture with the Ca2+ ionophore ionomycin. These cells were found not to express bcl-2 protein. By contrast, Burkitt lines which have drifted towards a lymphoblastoid cell line phenotype and are resistant to the induction of apoptosis express high levels of the bcl-2 protein. The findings support the concept that the susceptibility of germinal center cells to entering apoptosis is associated with their lack of expression of bcl-2 protein. Aberrant expression of bcl-2 protein by some neoplastic germinal center cells may allow survival in situations where their normal counterparts die.

Surveillance of attempted suicide among adolescents in Oregon, 1988

In January 1988, Oregon became the first state to require hospital-based reporting of attempted suicide (AS) in all adolescents less than 18 years old. From January to December 1988, 644 cases of AS were reported (annual rate of 214 per 100,000 population, ages 10 to 17 years). We compared these 644 cases of AS with all 137 Oregon adolescents less than 18 years old who committed suicide in Oregon during the 10-year-period 1979 through 1988, and found that the strongest predictor of outcome was method used.

Inhibition of interleukin 4-promoted CD23 production in human B lymphocytes by transforming growth factor-beta, interferons or anti-CD19 antibody is overriden on engaging CD40

Interleukin 4 (IL 4) is an essential component in the sequence of events directing IgE synthesis in uncommitted B lymphocytes. An early consequence of IL 4's interaction with the B cell is the induction of CD23, a low-affinity receptor for IgE (Fc epsilon RII). The present study was designed to explore the detailed regulation of this event. First, we report that transforming growth factor-beta (TGF-beta) is a potent inhibitor of IL 4-promoted CD23 production in human B lymphocytes. The level of inhibition achieved with TGF-beta was greater than that obtained with interferons, or with a monoclonal antibody (mAb) to CD19. Next, we identified three signals, each of which was capable of selectively counteracting the inhibitors of IL 4-promoted CD23 production: (a) the engagement of surface CD40 antigen with mAb was found to override the influence of all the inhibitors of CD23 expression; (b) mAb to surface IgM overcame the inhibitory actions of TGF-beta and interferons but not that of CD19 ligation; (c) ligation of surface CD72 counteracted the inhibition mediated by TGF-beta but not that generated by interferons or anti-CD19 antibody. Inhibition of the IL 4 signal appeared to be selective for the pathway leading to CD23 induction: none of the inhibitors profoundly altered IL 4's ability to enhance surface IgM expression. The study has ramifications for the understanding of events leading to the promotion of IgE synthesis and consolidates the notion of a central role for CD40 in B cell regulation.

Stimulation of B lymphocytes via CD72 (human Lyb-2)

A monoclonal antibody to CD72, the 45-kDa human homolog of murine Lyb-2, was found to augment selective activation pathways in tonsillar B lymphocytes. By itself, CD72 antibody provided a weak direct stimulus to resting B cells as assessed by [3H]dThd incorporation; this was modestly enhanced on the addition of interleukin 4 (IL4) or following ligation of surface CD40. CD72-delivered signals were more evident in co-stimulation assays with phorbol ester and with a synergistic combination of IL4 and CD40 antibody, but not with calcium ionophore or a CD23 antibody; rapidly cycling B cells were refractory to signaling via CD72 whether or not other co-stimuli were present. A unique feature of the CD72-delivered signal was its ability to enhance synergistically stimulations triggered with immobilized antibody to IgM, while failing to augment responses initiated by soluble anti-mu. On direct culture of resting B lymphocytes with CD72 antibody, an approximately twofold increase in the expression of major histocompatibility complex class II DQ antigen was observed, an augmentation similar to that achieved with IL 4; CD72 antibody also mimicked IL 4 in its ability to drive G0 cells into the early G1 phase of cell cycle. In contrast to IL 4-promoted stimulation, CD72 antibody failed to up-regulate the surface expression of either IgM or the CD23 antigen. CD72 expression itself was found to be weak on resting B lymphocytes and was modestly enhanced following culture with IL 4. The findings are discussed with reference to observations made on the triggering of murine B lymphocytes through Lyb-2 and within the context of previously defined human B cell activation pathways.

Recombinant 25-kDa CD23 and interleukin 1 alpha promote the survival of germinal center B cells: evidence for bifurcation in the development of centrocytes rescued from apoptosis

Germinal centers contain a proliferating pool of centroblasts which give rise to non-dividing centrocyte. Centrocytes are programmed to die by apoptosis unless they receive a positive signal for rescue. Rescue, in vivo, is likely to be dependent, initially, on interaction with antigen held on follicular dendritic cells (FDC). A subset of FDC located in that part of the germinal center furthest from centroblasts is particularly rich in CD23. Supernatants containing high levels of soluble CD23 were found not only to encourage the survival of germinal center B cells but also to promote their differentiation toward a plasmacytoid morphology; these activities were diminished following removal of CD23 from the supernatants. Recombinant 25-kDa CD23 was initially found to be incapable of providing the signal for germinal center cell development but on the addition of interleukin 1 alpha which, by itself, was inactive, rescue and differentiation of germinal center B cells were now achieved. Apoptosis in germinal center cells could also be prevented by the ligation of surface CD40 with monoclonal antibody: however, rescue via this pathway was not accompanied by plasmacytoid differentiation. These findings provide a functional rationale to the high level expression of CD23 found within a discrete subset of FDC and indicate a bifurcation in the development of germinal center B cells following their rescue from apoptosis.

Strategies to increase preventive care in general practice

OBJECTIVE

To develop strategies to overcome barriers to preventive care in general practice.

METHOD

Participants invited to attend a one-day workshop ranked barriers to preventive care in a pre-workshop survey. During the workshop, small groups generated strategies to overcome the most influential barriers. After the workshop, participants nominated strategies for implementation in the ideal world and in the realities of resource constraints.

PARTICIPANTS

Twenty-six participants representing general practice, medical academe, funding authorities, health policy planners, researchers, medicopolitical organisations and consumers.

RESULTS

The surveys yielded preferred strategies for implementation in the ideal world and 10 preferred strategies for implementation given likely resource constraints.

CONCLUSIONS

Authoritative guidelines are needed to guide clinical practice and to evaluate research. Other comprehensive strategies to overcome barriers to preventive care must be implemented and evaluated for effectiveness and acceptability in field experiments before wider implementation. The controlled implementation and evaluation of these strategies requires genuine collaboration amongst clinicians, health policy planners, researchers, funding authorities and general practice academe.

A prominent antigenic surface polypeptide involved in the biogenesis and function of the vaccinia virus envelope

Polypeptides of the vaccinia virus envelope exposed on the surface were identified by means of sulfo-N-hydroxysuccinimidobiotin as a surface tag. Among surface expressed polypeptides is the 35-kDa antigen, previously designated Ag35. Both monoclonal (mAb) and monospecific affinity pure antibodies directed against Ag35 neutralized vaccinia infectiousness, indicating that this prominent surface antigen has a function during early virus-host cell interactions. The binding of several monoclonal antibodies to various regions of Ag35 was tested by reacting CNBr fragments, derived from the polypeptide, employing Western blotting. All mAbs tested reacted with the same region of Ag35. Estimation of the molecular weights (MW), based on migration of the CNBr peptides in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, revealed that those partial digestion products which contained a proline-rich 99 amino acid limit digest fragment were present at a position approximately 12.5 kDa larger than that predicted from the DNA sequence. By contrast, partial and limit digest products lacking the proline-rich fragment migrated to the MW position expected from the length of the DNA sequence. This observation demonstrates that departure from a predicted 22.3 kDa to an anomalous MW of Ag35 is conferred by the proline-rich peptide. The surface location of Ag35 was confirmed by immune electron microscopy. In a competition test the binding specificity of mAb and affinity-purified antibodies at the surface of virions could be demonstrated. Evidence for an association of Ag35 with the virus envelope at various stages during biogenesis of vaccinia was obtained by immune electron microscopy of whole mounts and thin sections. Presence of Ag35 as an early component of immature and mature virions, probably residing in the bilayer membrane structure was detected. A distinction can, therefore, be made between Ag35 and several other vaccinia envelope polypeptides which are synthesized as late functions and added during late stages of envelope assembly.

Activation of Epstein-Barr virus latent genes protects human B cells from death by apoptosis

Epstein-Barr virus (EBV), a human herpesvirus, establishes a persistent asymptomatic infection of the circulating B-lymphocyte pool. The mechanism of virus persistence is not understood but, given the limited lifespan of most B cells in vivo, it seems most likely that EBV-infected cells must gain access to the long-lived memory B-cell pool. Here we show in an in vitro system that EBV, through expression of the full set of eight virus-coded 'latent' proteins, can protect human B cells from programmed cell death (apoptosis), the deletion mechanism which normally restricts entry into memory. We have found that EBV-positive Burkitt's lymphoma (BL) cell clones retaining the original tumour cell phenotype and expressing only one of the virus latent proteins, the nuclear antigen EBNA 1, are extremely sensitive to apoptosis; in this respect they resemble the tumour's normal cell of origin found in the germinal centres of lymphoid tissue. By contrast, isogenic BL cell clones which have activated expression of all eight EBV latent proteins are resistant to the induction of apoptosis. The EBV latent proteins should therefore be seen not just as activators of B-cell proliferation but, perhaps more importantly, as mediators of enhanced B-cell survival.

Beta-2-adrenoceptor agonists up-regulate the in vitro Fc epsilon receptor II/CD23 expression on, and release from, the promonocytic cell line U937 and human blood monocytes

The possible regulatory role of beta 2-adrenoceptor agonists in the modulation of CD23 on the human promonocytic cell line U937 and on human monocytes was investigated. Incubation for 48 h in the presence of interleukin-4 (IL-4; 30 U/ml) induced optimal expression and release of CD23 on both U937 cells and human monocytes. When a beta 2-adrenoceptor agonist, either salbutamol or fenoterol, was added to U937 cells or monocytes both the IL-4-induced CD23 expression and release were markedly up-regulated. This effect was dose-dependent, starting at 10 nM and reaching a maximum at 1 microM final concentration of either salbutamol or fenoterol. The potentiating effect of salbutamol and fenoterol on CD23 expression and release was not observed when a beta-adrenoceptor antagonist, either D,L-propranolol (1 microM) or butoxamine (1 microM), was added to the incubation medium. The alpha-adrenoceptor agonist norepinephrine (1 microM) was ineffective in enhancing the IL-4-induced expression and release of CD23 from U937 cells or human monocytes, demonstrating the specificity of the beta 2-adrenoceptor-mediated effect. In the absence of IL-4, a moderate but significant increase in the CD23 expression on U937 cells and human monocytes by these drugs was observed, as compared to the basal values. These results indicate that, besides their bronchodilator effect, beta 2-adrenoceptor agonists may regulate IgE-dependent processes.