Brucella fractions behave as nonspecific mitogens and polyclonal B-cell activators for human lymphocytes

Flow cytometry and morphology analysis of bone marrow in a child with brucellosis and hematologic manifestations

Constitutional symptoms and pancytopenia are occasionally the initial presentation of pediatric brucellosis. Therefore, in endemic areas, in children with pancytopenia, both brucellosis and malignancy should be included in the deferential diagnosis. We report here a child with pancytopenia and hepatosplenomegaly as manifestations of brucellosis in whom bone marrow morphology and flow cytometry data revealed hemophagocytosis, left shift in myeloid cells and activation changes in antigenic properties of T and B lymphocytes and monocytes. The patient had an uneventful and complete recovery after appropriate antibiotic therapy. Our report demonstrates that bone marrow and flow cytometry findings in children with brucellosis may include significant reactive changes in hematopoiesis.

Spontaneous monoclonal immunoglobulin-secreting peripheral blood mononuclear cells as a marker of disease severity in multiple myeloma

Peripheral blood from patients with multiple myeloma (MM) contains a small number of plasma cells related to the bone marrow tumour cells by their cytoplasmic immunoglobulin (Ig), their cell membrane antigen expression and/or their gene rearrangements, but hitherto the monoclonal Ig (M-Ig) production by circulating cells has not been reported. Using a two-colour ELISPOT assay, Ig-secreting cells (Ig-SCs) were detected in the blood of 28 MM and five Waldenstrom's macroglobulinaemia (WM) patients. The number of cells that spontaneously produced an Ig isotype similar to that of the M-Ig in serum was greater than that of the other Ig-SCs. MM patients presented an excess of circulating heavy-chain (alpha or gamma) Ig-SCs (0.38% of the PBMC) with kappa or lambda light chains (0.48%) compared with the number of cells secreting the other heavy- (0.02%) and light-chain isotypes (0.03%). WM patients also presented high numbers of cells secreting the mu-heavy-chain isotype (0.66%). The Ig synthesized in vitro was characterized as monoclonal, and the M-Ig secretory capacity of the peripheral blood cells was similar to that observed for Ig-SCs from polyclonal activated B cells in vivo. The number of these monoclonal cells was significantly increased in patients in an advanced stage of MM (I/II vs. III, P < 0.001) and correlated with the serum beta-2 microglobulin concentration (r = 0. 69; P < 0.0003). The number of M-Ig-SCs in MM patients could be a useful marker for evaluating the progression of multiple myeloma.

Peripheral lymphoid hyperplasia and central lymphoid depletion in mice treated with a bacterial B-cell mitogen (F3'EP-Si/p90)

In order to further understand the mechanism mediating the mitogenic and immunosuppressor effects of p90, a protein produced by Streptococcus intermedius, flow cytometric studies were performed on peripheral and central lymphoid organs of mice treated with this protein. p90 induced a strong blastogenic B-cell response in the spleen and lymph nodes, followed by a slight but significant polyclonal T-cell activation. B-cell repertoire analysis indicated that polyclonal B-cell responses affected similarly both CD5+ and conventional (CD5-) B cells in the spleen. Repertoire analysis of T cells failed to reveal any preferential stimulation of the V beta T-cell receptor (V beta-TcR) families studied. Peripheral lymphoid hyperplasia was observed concomitantly with central lymphoid depletion. In the bone marrow, pre-B and B cells were profoundly depleted, with a more pronounced effect on small pre-B cells. In the thymus, double-positive (CD4+CD8+) thymocytes were preferentially eliminated, with a relative enrichment of single positive (either CD4+ or CD8+) and double-negative (CD4-CD8-) thymocytes.

Protective effect of a T-cell-dependent immunosuppressive, B-cell-mitogenic protein (F3'EP-Si, or P90) produced by Streptococcus intermedius

The role of a previously described bacterial protein (F3'EP-Si), now designated P90, in the survival of Streptococcus intermedius in the host was investigated, and the immunosuppressive and B-cell-mitogenic effects of this protein were further characterized. C57BL6 mice treated with P90 were about 50 times more susceptible to infection with this bacterium than untreated mice. One of seven splenocytes of C57BL/6 mice were activated by P90. Marked splenomegaly was observed in mice treated with P90, with increased numbers of splenic mononuclear cells and polyclonal immunoglobulin-secreting plaque-forming cells. Peak responses were seen on day 3 for immunoglobulin M (IgM) and on day 5 for IgG, with an isotypic pattern consisting predominantly of IgG2a and IgG2b. When mice were treated with P90 before being primed with sheep erythrocytes, polyclonal immunoglobulin synthesis was accompanied by an ephemeral stimulation of the specific immune response against sheep erythrocytes that was quickly replaced by a dramatic immunosuppression. In contrast, when mice were treated with P90 after being primed, the polyclonal activation was comparatively much less evident and there was no suppression of the specific immune response. Immunosuppression was considerably reduced in mice thymectomized as adults or depleted of CD8+ cells. Adoptive transfer experiments showed that B cells obtained from P90-treated mice were less able to respond to an antigenic challenge, even in the presence of normal T cells, and that T cells obtained from P90-treated mice could actively suppress the specific immune response of normal B cells.

Antigens of Brucella abortus S19 immunodominant for bovine lymphocytes as identified by one- and two-dimensional cellular immunoblotting

Cellular immune responses are influential for protection against intracellular bacteria such as brucellae. Therefore, identification of Brucella abortus antigens that activate primed bovine lymphocytes is fundamental for discerning the breadth of cellular response in bovine brucellosis. Potentially antigenic components of B. abortus S19 were isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by nitrocellulose blotting. Specific one-dimensional blot segments induced proliferation of peripheral blood lymphocytes from all 25 of the vaccinated cattle tested and were defined as immunodominant. Individual proteins that stimulated lymphocyte proliferation were further characterized by two-dimensional cellular immunoblotting by two different approaches. Individual one-dimensional stimulatory blot segments were eluted, concentrated, and then subjected to two-dimensional cellular immunoblotting. Alternatively, entire two-dimensional gels containing all of the B. abortus components were blotted and nitrocellulose sections containing individual proteins were assayed for lymphocyte activation. Thirty-eight Brucella proteins that induced lymphocyte proliferation were resolved by both procedures. Phenotypic analysis of the proliferating cell population demonstrated the presence of CD4+, CD8+, and immunoglobulin M+ lymphocytes. Two immunogenic proteins, 12 and 31 kDa, identified by two-dimensional cellular immunoblotting, were subjected to partial N-terminal amino acid analysis. The 12-kDa protein was within the area of greatest lymphocyte proliferation, while the 31-kDa protein was chosen for comparison with a 31-kDa protein previously reported by others. A search of the National Biomedical Research Foundation protein data bank showed that the sequences were not homologous with other known proteins. Identification of Brucella proteins immunogenic for bovine lymphocytes provides an important step in distinguishing the various proteins involved in pathogenicity and/or disease resistance.

Low T- and B-cell reactivity is an apparently paradoxical request for murine immunoprotection against Streptococcus mutans. Murine protection can be achieved by immunization against a B-cell mitogen produced by these bacteria

C57BL/6 mice thymectomized as adults or depleted of CD4+ cells were much less susceptible than intact conventional mice to the B-cell mitogenic and specific immunosuppressive effects of a protein designated as F5'EP-Sm secreted by Streptococcus mutans. These mice were also considerably more resistant to infection by these bacteria than intact individuals. The immunosuppressor effect of F5'EP-Sm was also abrogated, however, in conventional intact mice when immunized intraperitoneally against heat-inactivated F5'EP-Sm. On the other hand, resistance to bacterial infection could be achieved by immunization of conventional intact C57BL/6 mice against heat-inactivated F5'EP-Sm by intraperitoneal or intradermal routes even when the animals were infected 3 months after immunization and even when the immunization procedure did not include Freund's adjuvant, which was the case with the intradermal route. Interestingly, the protection against the bacterial infection was accompanied by only a minor increase in specific serum antibodies against F5'EP-Sm. These results are discussed in the context of adequate strategies for immunoprotection against Streptococcus mutans and other micro-organisms which are secretors of substances that share both B-cell mitogenic and immunosuppressive properties and which are thus able to suppress the immune response by overstimulation of the immune system of the host.

Polyclonal B-cell activation in periodontitis

The evidence that periodontitis-associated bacteria contain potent PBA factors is very strong. Clearly, antibodies directed against non-oral antigens are produced in the inflamed periodontal lesion, and PBA appears to contribute to that production. It is also clear that B cells and plasma cells are the major cell types in the periodontal lesion. Furthermore, alterations in the regulation of B-cell responses to PBA factors are associated with severe periodontal disease. However, evidence demonstrating that activated B cells and plasma cells are directly involved in the pathogenic mechanisms leading to destruction of the periodontal support is still circumstantial. Polyclonal B-cell activation and potential pathways by which PBA-stimulated cells could be involved in periodontal destruction remain largely hypothetical. It appears that IL-1 is an important osteoclast-activating agent, and that LPS, which is a potent PBA factor in many systems, can elicit IL-1 production by B cells as well as by the monocyte/macrophage lineage. Recent data indicating that IL-1 is produced by numerous malignant B-cell lines lend support for the idea that B-cell IL-1 could be important in bone resorption. It is also likely that polyclonal activation may lead to production of autoantibody such as anti-type I and anti-type III collagens, and the destruction of self tissues through ADCC reactions, immune complex formation, and complement activation. Further research is needed to determine how the B cell/plasma cell may participate in tissue injury in periodontitis, and how the B-cell response to PBA factors is regulated.

Correlation between specific immunosuppression and polyclonal B cell activation induced by a protein secreted by Streptococcus mutans

The relationship between polyclonal B cell activation and immunosuppressor effects induced by F5'EP-Sm, a non-cytotoxic protein secreted by Streptococcus mutans, was studied in C57BL/6 mice. Mice treated with F5'EP-Sm exhibited a considerable increase in splenic nonspecific Ig plaque-forming cells (PFC) compared with untreated mice. The isotypic pattern of non-specific PFC responses favours IgG2a approximately equal to IgG2b greater than IgG3 greater than IgG1 approximately equal to IgM, when taken as a ratio between treated and untreated animals. When F5'EP-Sm was administered 2 days before immunization with sheep red blood cells (SRBC), the non-specific PFC production was accompanied by an ephemeral increase in specific PFC against SRBC 1 day after immunization, which was quickly replaced by a strong immunosuppression. In contrast, when F5'EP-Sm was injected after priming, there was little or no demonstrable suppression of specific PFC, and the increase of non-specific PFC was much less evident. The kinetic curves representing increase or decrease in relation to controls of specific and non-specific PFC are almost mirror images in each of the isotypes. The in vivo suppressor effect was abrogated in thymectomized mice, although the involvement of the T cell compartment is probably secondary to the B cell mitogen effect, since T-depleted spleen cells proliferate and synthesize non-specific Ig when stimulated in vitro with F5'EP-Sm.

Serum- and cell-mediated immune protection of mouse placenta and fetus against a Brucella abortus challenge: expression of barrier effect of placenta

When mice are intravenously inoculated with a virulent Brucella abortus strain at day 12 to 14 of pregnancy and killed three to five days later, colonization of placentae, fetuses and spleens can be estimated by the frequency and level (bacterial count) of infection and by linkage between individual placental and paired fetal infections. This linkage indicates the placental barrier effect, defined as the number of non-infected fetuses linked to 100 colonized placentae. Immune mice serum raised against two Brucella fractions injected one day before challenge (1) restricted the placental colonization (the dose required to infect 50 per cent placentae was increased by 50 to 70 times compared to controls), (2) decreased the level of splenic and placental infection, and (3) increased the barrier effect so that most fetuses were protected even when linked to a heavily infected placenta. Immune (B + T) spleen cells from mice vaccinated with a Brucella cell-wall fraction transferred to recipients seven to eight days before mating, that is, 22 days before challenge (1) restricted the frequency of placental and fetal colonization, (2) decreased the level of splenic, placental and fetal infections, and (3) increased the barrier effect. However, separated B- and T-cells were less active, in particular on the level of fetal infection. In contrast with serum, the cells did not decrease infection of the fetuses linked to heavily infected placentae.

Strong mitogenic effect for murine B lymphocytes of an immunosuppressor substance released by Streptococcus intermedius

A noncytotoxic protein substance, produced by Streptococcus intermedius, with very potent immunosuppressive properties (F3'EP-Si) was tested for lymphocyte mitogenic activity. Although devoid of T-cell mitogenicity, F3'EP-Si stimulated proliferation and led to high numbers of plaque-forming cells in cultures of normal or T-cell-depleted, small or large splenic B cells from both lipopolysaccharide-responding and -nonresponding mice. The B-cell mitogenic activity of F3'EP-Si was quantitatively comparable to that of lipopolysaccharide, and the simultaneous exposure to both mitogens stimulated additive B-cell responses. Injection of F3'EP-Si into normal mice resulted in increased numbers of spleen cells, higher rates of mitotic activity, and very large numbers of plaque-forming cells, predominantly of the immunoglobulin G2a and -b isotypes. In preliminary experiments, the analysis of surface markers among the lymphocytes participating in the blastogenic response in vivo revealed a T-cell component in the response to F3'EP-Si. These observations are discussed in the context of the immunosuppressive activity of this and other microbial substances.