B-cell differentiation in vivo

Is there a single differentiation pathway for all antibody-forming cells in the spleen?

By incubating tissue sections with antigen (or hapten)-enzyme conjugates, followed by enzyme cytochemistry(1-4), N. van Rooijen and his colleagues have been able to study the development and localization of specific antibody-producing cells in the spleen of animals after a single intravenous antigen injection. Variations in this method(5-11) allowed them to compare the localization patterns of cells producing different antibodies and to determine simultaneously their Ig isotype. Studies on primary and secondary immune responses against thymus-dependent and thymus-independent antigens lead them to postulate that there is one 'differentiation pathway' for antibody-forming cells in the spleen, independent of the antigen and the type of immune response.

In situ localization of cell synthesis and proliferation in periodontitis gingiva and tonsillar tissue

OBJECTIVE

Previous work indicates that large numbers of B and T cells accumulate in the periodontal soft tissues although we know little about cellular synthetic activity and proliferation in this site. The aim of this study was to examine lymphocytic cell synthetic activity and proliferation in periodontitis gingiva and compare this to a known site of leucocyte proliferation, namely the oropharyngeal tonsils.

MATERIALS AND METHODS

Messenger RNA (mRNA) and 28S ribosomal (28S rRNA) expressing cells in formalin-fixed/paraffin-embedded gingival and tonsillar tissue sections were detected by in situ hybridisation (ISH) using poly-deoxyribothymidine and 28S probes respectively. In addition S-phase proliferating and cycling cells were also detected by ISH with histone probes and by Ki-67 immunohistochemistry. Ten gingival biopsy samples were obtained from adult periodontitis patients and five tonsillar biopsies from tonsillectomy patients.

RESULTS

Both mRNA and 28S rRNA-expressing cells were detected in all the samples tested. Plasma cells showed the strongest signal for the two probes and slight to moderate staining could be seen in epithelium, fibroblasts and endothelial cells. In contrast, gingival lymphocytes were either weakly stained or were unstained for these probes of synthetic activity. In tonsils, most lymphocytes in germinal centres showed moderate staining and mantol zone cells were much more weakly stained. In gingival samples, histone mRNA-expressing and cycling (Ki-67) cells were detected in 4/10, 10/10 cases respectively. These positive cells were mainly basal and suprabasal epithelial cells and a few mononuclear cells, whereas most germinal centre lymphocytes (B cells) were positive for this probe. The number of Ki67 positive cells was greater than histone mRNA bearing cells both in gingiva and tonsillar tissue. In contrast, mantol zone cells (mainly T cells) were sparsely stained by probes of cell proliferation.

CONCLUSION

These results indicate that local proliferation of B cells does not occur in periodontitis gingiva in contrast with tonsillar tissue, although plasma cells showed strong synthetic activity in both tissues. T cells did not appear to proliferate greatly nor undergo active synthesis in either of these tissues. These findings substantiate previous hypotheses that specific leucocytes predominate in the gingival tissue through selective homing rather than by local proliferation.

To B, or not to B: that is the question

Irrespective of the prevailing fashion, Germinal Centre Conferences (GCC) have treated the immune system in a determinedly holistic manner. At the recent 10th GCC* the advantages of this approach were demonstrated in elegant new schema for lymphocyte development, accessory cell function, tolerance and autoimmunity, and for the organization and function of mucosal defence. This report concentrates on only one aspect of the meeting - the development of an integrated view of the natural history of B cells.

Zonal distribution of immunoglobulin-synthesizing cells within the germinal centre: an in situ hybridization and immunohistochemical study

Immunohistologic studies have shown that synthesis of cytoplasmic immunoglobulin (cIg) is a normal function of some follicle centre cells (FCCs). The mechanisms regulating this synthesis of immunoglobulin and its function within the germinal centre are still poorly understood. In this study we applied a recently developed in situ hybridization method for the detection of kappa and lambda light chain mRNA to reactive lymph nodes and tonsils in order to investigate further the immunoglobulin-synthesizing cells of the germinal centre. FCCs containing detectable levels of light chain mRNA corresponded closely to cells containing cIg. The detection of light chain mRNA rather than its immunoglobulin product was found to be an advantage in that problems associated with the detection of extracellular immunoglobulin were eliminated. This was most apparent in germinal centres where the absence of 'network' immunoglobulin led to the observations that immunoglobulin-synthesizing FCCs are predominantly small centrocytes and that in a proportion of germinal centres they localize in that part of the light zone closest to the dark zone. This zonal distribution of immunoglobulin-synthesizing FCCs raises the possibility of further functional and micro-environmental subcompartments within the light zone.

The "in situ" immune response in lymph nodes: a review

For many years data on the development of specific antibody-forming cells in lymph nodes were incomplete, fragmentary, and even contradictory. A number of recent studies have been performed, concerning 1) their overall architecture; 2) migration of B-lymphocytes; 3) localization of accessory cells and T-lymphocytes which are believed to be involved in humoral immune responses; and 4) localization patterns of specific antibody-forming cells developing during thymus dependent and thymus independent immune responses. Comparison of these new results with those of earlier studies suggests a single route of migration followed by all cells which will differentiate into antibody-forming cells. During their differentiation into antibody-forming plasma cells, antigen reactive B-cells migrate along the required accessory cells and/or T-lymphocytes.

Effects of steroids with different endocrine profiles on the development, morphology and function of the bursa of Fabricius in chickens

This paper describes the effect of various steroids on the anlage of the bursa of Fabricius in chickens. The steroids were administered by dipping embryonated eggs on the third day of incubation in ethanolic solutions of these steroids. The results with about 30 different steroids show that the capacity to inhibit the development of the bursa does not correlate with the endocrine properties of these steroids as measured in routine screening tests for androgenic, anabolic, progestational and oestrogenic activities or with the relative binding affinities for various endocrine receptors. More elaborate studies with several representative steroids show that testosterone (10 mg/ml), nandrolone (10 mg/ml), 11 alpha-hydroxynandrolone (10 mg/ml), ethylestrenol (1 mg/ml), lynestrenol (1 mg/ml), and Org OD14 [tibolone] (0.1 mg/ml) induce also histomorphological changes in the remaining bursa tissue still present in 10 day- and 53-day old chickens and in the bursa-dependent sites of their spleens (53-day old chickens only). Testosterone and lynestrenol induced smaller changes than nandrolone or ethylestrenol. Tibolone and 11 alpha-hydroxynandrolone were more effective than nandrolone. All drugs, except testosterone and lynestrenol, imparied antibody formation to Newcastle Disease Virus and decreased the serum levels of total IgG, but not of total IgM. Also these effects were not correlated with endocrine properties. In other studies (for references, see text) we found that several of these steroids, notably tibolone, favourably influence the course of spontaneous autoimmune diseases of NZB/W mice and Obese Strain chickens. Since this autoimmunosuppression is likely to be caused by inhibitory effects on bursa or bursa equivalent, we may use this approach for developing medically useful autoimmunosuppressive steroids with minimal endocrine effects.

The organization of cell populations within lymph nodes: their origin, life history and functional relationships

The normal lymph node comprises a superficial cortex, a deep cortex or paracortex and a medulla. In each of these regions there are three kinds of spaces: an intralymphatic space, an intravascular space and an extravascular space or interstitium. Both the vascular endothelium and the lymphatic endothelium are specialized in these different regions. The cell types in lymph nodes comprise lymphoid cells, accessory or non-lymphoid cells and stromal cells, and within these cell types a number of different sub-types can now be identified by means of enzyme- and immunocytochemistry. Based predominantly on experimental studies, the origin, migratory patterns, localization, inter-relationships and interactions between these various cells are reviewed.

Functional anatomy of germinal centers

This year we celebrate the first centennial of the discovery of germinal centers by Flemming in 1884. The present paper reviews and adds new data to the functional anatomy of a germinal center. Emphasizing its reactive nature, we first describe a germinal center reaction and then deal with its infrastructural aspects and constituent cell populations, both lymphoid and nonlymphoid. Elements involved in the de novo formation of a germinal center, like antigen, T cells, and the mysterious germinal-center-precursor cell, are discussed. Next, attention is paid to the requirements for lymphoid cells to migrate into germinal centers, and novel features of germinal-center-seeking cells are presented. Subsequently, we discuss kinetic aspects of the high proliferative activity in a germinal center; and finally a description of the functional capacities of germinal-center-derived cells, such as B memory cells and IgM-antibody-forming cell precursors, completes this picture of present-day knowledge of the germinal center, a structure which has yet to reveal its last secrets.

Double immunocytochemical evidence for a clonal development of specific antibody-containing cells in the rabbit spleen

Rabbits were intravenously primed with the antigens human serum albumin (HSA) and bovine gamma globulin (BGG). The antigens were given simultaneously, or at an interval of 1, 2, or 4 days. After 2 months an intravenous booster injection with both antigens was given simultaneously. The localization pattern of anti-HSA-antibody-containing cells and of anti-BGG-antibody-containing cells in the spleen was determined during both the primary and secondary immune response. Anti-HSA-antibody-containing cells and anti-BGG-antibody-containing cells were not distributed randomly but, rather, were found in defined groups during the induction of an immune response. The most probable explanation for this grouping is that lymphoid cells, once triggered to proliferation by a particular antigen, show a clonal development in the spleen. During their proliferation and successive antibody formation, they migrate only slowly, so that they remain close together. Specific-antibody-containing cells were also detected in the popliteal lymph nodes and in the appendix of the rabbits.

Lymphocyte migration across major histocompatibility barriers in splenectomized rats

Localisation and migration patterns of iv injected radio-labelled thoracic duct (TD) lymphocytes were studied in particular with regard to passage through lymph nodes and re-entry into thoracic duct lymph. To avoid unwanted splenic sequestration of migrating lymphocytes presenting alloantigens to the recipient, only splenectomized recipients were used. Donor cells and recipients differed at the MHC (RT-1) locus, either in fully allogeneic (AO -- greater than BN and v.v.) or semi-allogeneic (AO -- greater than AO X BN and v.v.) combinations. In two of these combinations (BN -- greater than AO and AO X BN -- greater than AO) deficient output in TD lymph correlated with deficient localisation in lymph nodes and high amounts of radioactivity in the liver. In the other allogeneic combination (AO -- greater than BN), however, high TD output (i.e. when compared with the syngeneic combination BN -- greater than BN) correlated with good localisation in lymph nodes and low (control) levels of radioactivity in the liver. It was postulated that lymphocyte migration from blood to lymph under these circumstances can only be studied as an artifact secondary to whether or not migrating cells are removed from the circulation before they can reach and cross HEV's. These Allogeneic (or Altered) Lymphocytes Removing Tissues (by definition: Extranodular) may (conceptually) be comprised within one system: ALERT. It is our working hypothesis that the study of lymphocyte migration across (major) histocompatibility barriers is seriously impaired by the functioning of ALERT. It might be worthwhile to try and create conditions in which interference by this system is prevented, e.g. by using tolerant animals or bone-marrow chimeras.

Plasma cells and their precursors. III. Late phases of anti-bovine serum albumin IgG antibody responses depend upon newly produced IgG B-memory cells

The sequential appearance of the IgG antibody clones constituting the primary, secondary or tertiary response to BSA was studied in individual rabbits by relating antibody titers, antibody affinities, and clonal spectra obtained by IEF. The results showed that after a single i.v. injection of BSA, the primary response IgG antibodies peaked at day 11 and had a constant and low average affinity during the first 20 days. A slow rise of affinity was observed during the following 20 days. In this period, new IgG antibody clones appeared, though antibody titers decreased. A number of these newly appearing, so-called late-phase clones were isolated by preparative IEF. Their affinities to BSA were high. Secondary responses showed the rapid rise of both titers and antibody affinities typical for the activity of B-memory AFC. One animal immunized for a tertiary response showed a still further increase of antibody affinity in its late phase. These results, together with those described in two earlier papers (1, 2), demonstrate that primary immunization, apart from triggering preexisting IgG AFCP into production of antibodies having low affinity, elicits the origination of IgG (B-memory)-AFCP capable of producing high affinity IgG upon antigenic triggering, and show that some of these may already be triggered during the ongoing response, thereby giving rise to the so-called late phase in the primary IgG antibody response.

Antigen-trapping cells in Peyer's patches of the rat

Peyer's patches (PP) of rats were studied with immunocytochemical, enzyme cytochemical, and electron microscopic techniques. Special attention was paid to the non-lymphoid antigen-trapping cells. Follicular dendritic cells, morphologically comparable to those present in spleen and lymph nodes, were found in the germinal centers of PP. Ia-positive cells with the morphological characteristics of interdigitating cells were seen in the interfollicular area. Thus, both types of antigen-presenting cells, characteristic for B- and T-cell areas, respectively, were present in PP.

Follicular dendritic cells in lymph nodes after x-irradiation

Follicular dendritic cells (FDC), non lymphoid cells present in lymph follicles, are characterized by numerous cytoplasmic processes retaining antigen-antibody complexes. Their origin, nature and function are unknown. Mice inguinal lymph nodes after 4.5 or 7.5 Gy X-irradiation were depleted of lymphoid cells. Ultrastructural observations during the first few days post-irradiation show that FDC are unaltered and possess dendritic processes enveloping dense material. Furthermore, they show intense metabolic activity. A lamina densa, never observed so well-developed in other lymph node cells, was detected around the nuclear envelope. The localization of junctions between FDC was analysed. FDC preserve their typical cytoplasmic processes even if lymphoid cells are rare. The latter thus seem not to be responsible for the maintenance of FDC integrity or their development. The possible role of this for antibody production is discussed. Irradiated lymph nodes of lymphoid cells are highly convenient for studying FDC. Isolation of FDC from irradiated lymph organs would seem to be possible.

Plasma cells and their precursors. I. Preexistent antibody-forming cell precursors dominate the anti-sheep red blood cell and anti-human gamma globulin IgG antibody response

Rabbits were immunized by a single i.v. injection of SRBC or HGG and were bled serially. Sera were analyzed by IEF using the gel overlay technique to investigate clonal patterns of circulating IgG antibodies. Clonal patterns of primary-response IgG antibodies were quite stable over a period of months, showing that this response is dominated by plasma-cell precursors already present at the time of antigenic stimulation. In the late phase of the primary IgG response, new bands were occasionally observed in the antibody spectra, suggesting the presence and triggering of newly formed plasma-cell precursors. Primary-response antisera had individually unique clonal patterns. In secondary-response antisera elicited by a second single i.v. injection, the IEF spectra were found to be more complex and could be individually distinguished only with difficulty.

Plasma cells and their precursors. II. Kinetics of B-memory cell production in rabbits

Rabbits were irradiated with 4.5 Gy in order to eliminate completely preexisting antibody-forming cell precursors. Sheep red blood cells were administered 24 h or 8 days after irradiation in order to induce the production of IgG B-memory AFCP. Resulting B-memory cells were triggered into antibody synthesis by a second dose of SRBC given 8 days after the challenge; the resulting IgG antibody clones were analyzed by isoelectric focusing. Memory IgG antibody clones were detectable from the third day after secondary immunization onward. It is concluded that antigen administered as early as 24 h after the irradiation induces B-memory cell production equally well as primary immunization 8 days after the irradiation. This B-memory cell production proceeds in the absence of detectable primary IgG antibody formation. Irradiated non-immunized rabbits showed spontaneous reappearance of IgG-AFCP with specificities to SRBC. In sharp contrast to the specifically induced production of B-memory IgG-AFCP mentioned above, this process took more than two months to reach potentialities comparable to those of "preexistent" AFCP present in normal, control rabbits.

Experimental granulomas induced by mycobacterial immune complexes in rats

After BCG were complexed with homologous anti-BCG serum IgM was found to be firmly bound to the organisms. Preparations were made at antigen/antibody equivalence and at two-fold and four-fold antibody excess. They were injected subcutaneously into rats. At equivalence the mixtures provoked rapidly developing necrotic destructive lesions containing many bacilli. Injection of mixtures at antibody excess caused the rapid formation of epithelioid cell granulomas without necrosis and containing few bacilli. Compared with the injection of BCG alone, injection of comparable numbers of IgM-complexed bacilli at equivalence led to more rapid necrosis but also more rapid resolution of the granulomas which followed, Delayed-type skin reactions to PPD took longer to develop after injection of complexed BCG, usually as long as 4 weeks. The delay varied directly with the degree of antibody excess. This failure to detect cell mediated immunity was reflected in the histology of the draining lymph nodes which differed strikingly from that seen after injection of BCG alone. In animals injected with bacilli in excess antibody, epithelioid cell granulomas formed and viable bacilli were apparently eliminated before skin reactions to PPD developed. It is concluded that circulating immunoglobulin, perhaps IgM in particular, is likely to play a significant role in the pathogenesis of tuberculosis and similar diseases and that the relative ratio of antigen to antibody within the lesions may be crucial in influencing the balance between tissue destruction and healing.