Splenic B cells function as immunogenic antigen-presenting cells for the induction of effector T cells

Tamoxifen Suppresses the Immune Response to Plasmodium berghei ANKA and Exacerbates Symptomatology

Malaria is the most lethal parasitic disease in the world. Mortality and severity in symptoms are higher in men than women, suggesting that oestrogens, which are in higher concentration in females than in males, may regulate the immune response against malaria. Tamoxifen, a selective oestrogen receptor modulator used in breast cancer treatment due to its antagonistic effect on oestrogen receptors α and β, is also studied because of its potential therapeutic use for several parasitic diseases. However, most studies, including one in malaria, have not addressed the immunomodulatory role of tamoxifen. In this work, we evaluated the effect of tamoxifen on the immune response of CBA/Ca mice against Plasmodium berghei ANKA. This study showed for the first time that tamoxifen increased parasite load, aggravated symptoms by decreasing body temperature and body weight, and worsened anaemia. Additionally, tamoxifen significantly increased the splenic index and the percentages of CD4⁺ and NK⁺ cells on day eight post-infection. By contrast, tamoxifen decreased both CD8⁺ and B220⁺ populations in the spleen and decreased the serum levels of IL-2, IL-6, and IL-17. Our findings support the notion that tamoxifen is a potent immunomodulator in malaria-infected mice and suggest caution when administering it to malaria-infected women with breast cancer.

Graft-versus-host disease: part I. Pathogenesis and clinical manifestations of graft-versus-host disease

Approximately 25,000 allogeneic hematopoietic cell transplants are performed worldwide each year for a variety of malignant and non-malignant conditions. Graft-versus-host disease represents one of the most frequent complications and is a major source of long-term morbidity and mortality. Whereas acute graft-versus-host disease is induced by recognition of host tissues as foreign by immunocompetent donor cells, the pathogenesis of chronic graft-versus-host disease is not as well understood, and continues to be a major treatment challenge. Part I of this two-part series reviews the epidemiologic factors, classification, pathogenesis, and clinical manifestations of acute and chronic graft-versus-host disease. Part II discusses the topical, physical, and systemic treatment options available to patients with graft-versus-host disease.

Inhibition of antigen trafficking through scavenger receptor A

B cell acquisition and presentation of specific autoantigens (auto-Ags) are thought to play an important and complex role in autoimmunity development. We previously identified scavenger receptor A (SR-A) as an early target in altering B cell-mediated autoimmunity. SR-A is highly expressed on professional antigen-presenting cells such as macrophages (MΦs) and dendritic cells (DCs). In this study, we demonstrate that SR-A is responsible for controlling B cell interactions with DCs/MΦs to promote Ag transfer from B cells to DCs/MΦs. We established a high-throughput ELISA-based screen to identify novel SR-A inhibitors, the specificity of which was determined by dose dependence and Biacore surface plasmon resonance testing. We identified small molecule inhibitors (SMIs) able to reduce SR-A-mediated Ag transfer in human cells. In particular, the SMIs prevented SR-A-positive cells from accumulating/loading Ag over time. Furthermore, we determined that one SMI, sennoside B, can reduce SR-A-mediated capture of B cells. Finally, SMI-mediated decreases in Ag transfer or accumulation reduced T cell proliferation in vitro and in vivo. These observations demonstrate that B cell-DC/MΦ interactions are conducive to promoting Ag trafficking between these cell types via SR-A. Inhibitors of SR-A may provide a novel therapeutic strategy in ameliorating autoimmune disease development.

B cells modulate T cells so as to favour T helper type 1 and CD8+ T-cell responses in the acute phase of Trypanosoma cruzi infection

In this study, we have evaluated the production of pro- and anti-inflammatory cytokines and the formation of central and effector memory T cells in mice lacking mature B cells (mu MT KO). The results show that Trypanosoma cruzi infection in C57Bl/6m mu MT KO mice is intensified in relation to control mice and this exacerbation is related to low levels of inflammatory cytokines produced during the acute infection and the lower numbers of central and effector memory CD4(+) and CD8(+) T cells generated during the acute phase of the infection. In addition, a marked reduction in the CD8(+) T-cell subpopulation was observed in mu MT KO infected mice. In agreement to this, the degree of tissue parasitism was increased in mu MT mice and the tissue inflammatory response was much less intense in the acute phase of the infection, consistent with a deficit in the generation of effector T cells. Flow cytometry analysis of the skeletal muscle inflammatory infiltrate showed a predominance of CD8(+) CD45Rb low in B-cell-sufficient C57Bl/6 mice, whereas the preponderant cell type in mu MT KO skeletal muscle inflammatory infiltrate was CD4(+) T cells. In addition, CD8(+) T cells found in skeletal muscle from mu MT KO infected mice were less activated than in control B-cell sufficient infected mice. These results suggest that B cells may participate in the generation of effector/memory T cells. In addition and more importantly, B cells were crucial in the maintenance of central and effector memory CD8(+) T cell, as well as the determination of the T cell cytokine functional pattern, and they may therefore account for critical aspects of the resistance to intracellular pathogens, such as T. cruzi.

Heat shock protein 60 activates B cells via the TLR4-MyD88 pathway

We recently reported that soluble 60-kDa heat shock protein (HSP60) can directly activate T cells via TLR2 signaling to enhance their Th2 response. In this study we investigated whether HSP60 might also activate B cells by an innate signaling pathway. We found that human HSP60 (but not the Escherichia coli GroEL or the Mycobacterial HSP65 molecules) induced naive mouse B cells to proliferate and to secrete IL-10 and IL-6. In addition, the HSP60-treated B cells up-regulated their expression of MHC class II and accessory molecules CD69, CD40, and B7-2. We tested the functional ability of HSP60-treated B cells to activate an allogeneic T cell response and found enhanced secretion of both IL-10 and IFN-gamma by the responding T cells. The effects of HSP60 were found to be largely dependent on TLR4 and MyD88 signaling; B cells from TLR4-mutant mice or from MyD88 knockout mice showed decreased responses to HSP60. Care was taken to rule out contamination of the HSP60 with LPS as a causative factor. These findings add B cells to the complex web of interactions by which HSP60 can regulate immune responses.

Reduced immunogenicity of long-term, passively enhanced rat renal allografts and passive transfer of graft protection

Enhancing alloantiserum was produced by immunizing male BD IX inbred rats with density gradient separated nylon-wool adherent spleen lymphocytes from male rats of the major histocompatibility complex (MHC) different inbred strain Sprague-Dawley (SD). Long-term surviving (BD IX X SD) F1 to BD IX kidney grafts were achieved by treating the recipients with 1 ml alloantiserum at the time of transplantation. After greater than 100 days 7 passively enhanced F1 kidneys were retransplanted into naive BD IX rats. Four out of 7 secondary recipients, producing only low levels of lymphocytotoxic antibodies, survived for greater than 100 days, 3/7 rats died of surgical or infection complications. Twenty-one naive BD IX recipients of normal F1 kidneys were treated with serum (1 ml i.v.) and/or spleen lymphocytes (1 X 10(7) i.v.) obtained from the long-term survivors. An indefinite graft survival was achieved in 13 out of 21 rats. After greater than 150 days 6 out of these 13 passively enhanced F1 kidneys were retransplanted into naive BD IX rats which were challenged at the time of grafting with 4 X 10(7) SD lymphocytes to elicit rejection. Six out of 6 kidneys survived greater than 150 days. Thus, the long-term survival of rat kidney allografts in this model is associated with a strong reduction of graft immunogenicity as well as the development of suppressor cells and enhancing antibodies.

T cell development in B cell-deficient mice. II. Serological characterization of suppressor T cell factors (TsF1) produced in normal mice and in mice treated chronically with rabbit anti-mouse IgM antibodies

Serological analysis of idiotypic specificities present in azobenzenearsonate (ABA)-specific first-order suppressor T cell factors (TsF1) from C.AL-20 and BALB/c mice revealed a significant difference between TsF from these two strains of mice. The idiotypic composition of TsF1 from BALB/c mice appears to be more heterogeneous, and at least two different fractions can be readily identified. One bears the characteristic BALB/c-associated CRI(C) (crossreactive idiotype) determinants, and the other is non-CRI(C)-bearing. Analysis of ABA-specific TsF1 from animals lacking B cells uncovered a fundamental change in the expression of their idiotypic specificities. TsF from rabbit anti-mouse IgM (anti-mu)-treated C.AL-20 mice failed to express the characteristic CRI(A) determinants. Instead, they express CRI(C) specificities. Similarly, TsF1 from anti-mu-treated BALB/c mice did not express their characteristic CRI(C) specificities, but rather express CRI(A) determinants. These experiments provide strong evidence that the Igh restriction specificity of TsF is dictated by the particular idiotypic specificities expressed. They also clearly demonstrate that B cells and their products play an important role in establishing the idiotypic composition and repertoire of suppressor T cells.

T-cell mediated immunity in murine malaria. I. Induction of T-cell dependent proliferative responses to Plasmodium chabaudi

To investigate the mechanisms of cell mediated immunity to malaria, we studied different systems to measure specific activation of T lymphocytes by P. chabaudi antigens. Mice were primed by subcutaneous administration of parasite antigens followed by co-cultivation of lymphocytes taken from the draining lymph nodes in the presence of the priming antigen. A marked proliferative response was observed which was shown to be antigen specific, T-cell mediated and accessory cell dependent. Continuous T-cell lines were propagated in culture by repetitive restimulation in the presence of antigen and accessory cells, followed by expansion in a conditioned medium containing T-cell growth factors. These lines could be induced to proliferate to the priming antigen only in the presence of syngeneic accessory cells thus indicating that H-2 restriction operates in the recognition of plasmodium antigens by T cells. We also induced parasite specific T cells by the use of an in vitro primary 'education' system. Lymphocytes from unprimed mice were sensitized on parasite-fed macrophages and were then injected subcutaneously into each hind foot pad of syngeneic animals. This led to recruitment of antigen-reactive cells which were assayed in vitro by the ability of lymphocytes taken from the draining popliteal lymph nodes to proliferate in response to the sensitizing antigen. In vivo immunization with Plasmodium antigen fed macrophages also signalled antigen specific T cells that recruited reactive T cells in the draining lymph nodes.

Defective induction of antigen-reactive proliferating T cells in B cell-deprived mice. II. Anti-mu treatment affects the initiation and recruitment of T cells

Mice injected from day of birth onwards with rabbit anti-mouse IgM (antim-mu) antibodies were found to be B cell-deficient and defective for the induction of antigen-reactive proliferating T cells (TPRLF). This defective induction was not due to the absence of circulating antigen-specific antibodies since the daily injections of such antibodies during exposure to antigen did not restore the ability of anti-IgM treated animals to generate TPRLF. Analyzing the cellular events implicated in the induction of virgin antigen-reactive T cells, anti-mu-treated mice manifested impairment of the three interacting cell types involved in the induction of TPRLF. Thus, peritoneal and splenic antigen-presenting cells from such animals were impaired in their capacity to signal a primary antigen-specific T cell reaction. Their splenic lymphocytes could not function as initiator cells in transferring immunogenic signals to recruit TPRLF in normal recipients. Potent antigen-specific splenic initiator cells failed to induce the recruitment of specific TPRLF in anti-mu-treated mice. The defective induction of TPRLF in anti-mu-treated mice may be due to a functional impairment of cells expressing membrane-bound IgM molecules which seemingly play a central role in the transfer of immunogenic signals for the recruitment of antigen-specific circulating T cells. We suggest that splenic B cells function as initiators in the transfer of antigen-induced signals from peritoneal antigen-presenting cells to T cells. These seems to be the primary targets of anti-mu treatment.