Regulatory aspects of clonally expanded B-1 (CD5+ B) cells

Murine models of chronic lymphocytic leukaemia: role of microRNA-16 in the New Zealand Black mouse model

Mouse models are valuable tools in the study of human chronic lymphocytic leukaemia (CLL). The New Zealand Black (NZB) strain is a naturally occurring model of late-onset CLL characterized by B-cell hyperproliferation and autoimmunity early in life, followed by progression to CLL. Other genetically engineered models of CLL that have been developed include (NZB x NZW) F1 mice engineered to express IL5, mice expressing human TCL1A, and mice overexpressing both BCL2 and a tumour necrosis factor receptor-associated factor. The applicability to human CLL varies with each model, suggesting that CLL is a multifactorial disease. Our work with the de novo NZB model has revealed many similarities to the human situation, particularly familial CLL. In NZB, the malignant clones express CD5, zap-70, and have chromosomal instability and germline Ig sequence. We also identified a point mutation in the 3'-flanking sequence of Mirn16-1, which resulted in decreased levels of the microRNA, miR-16 in lymphoid tissue. Exogenous restoration of miR-16 to an NZB malignant B-1 cell line resulted in cell cycle alterations, suggesting that the altered expression of Mirn15a/16-1 is an important molecular lesion in CLL. Future studies utilizing the NZB mouse could ascertain the role of environmental triggers, such as low dose radiation and organic chemicals in the augmentation of a pre-existing propensity to develop CLL.

Relation between phenotype of tumor cells and clinicopathology in bovine leukosis

Thirty-three cases of enzootic bovine leukosis (EBL) and 14 cases of sporadic bovine leukosis (SBL) were examined by immunohistochemistry using 6 monoclonal antibodies against leukocyte differentiation molecules of bovine leukocytes. There were 17 cases of B-1a cell type, 10 cases of B-1b cell type and 6 cases of B-2 cell type in EBL, and 5 cases originating from B cells (B-2 cell type) and 9 cases originating from immature T cells in SBL. The average age for the EBL cases of B-1a cell type was 8.6 years, B-1b cell type was 6.5 years, and of B-2 cell type was 4.5 years. In cases of SBL, immature T cell type patients were younger than B-2 cell type ones. The lymphoma originating from B cells differed from that originating from T cells in morphology. In T cell tumors, the nucleus of tumor cells was round, the edge of the cytoplasm obvious, and tumor cells were sporadically present and proliferated. When compared with T cells, the region among B cells was obscure. But, there was no relation between phenotype and the histologic classification of tumor cells. In EBL, beyond the lymph node, tumors of B-1a and B-1b types had developed in the heart and abomasum, and those of the B-2 type tended to occur in liver. In SBL, B-2 type and T type cells formed tumors in the liver, kidney, thymus, and one case of T-cell type tumor formed on the skin. We would like to propose a new classification of bovine leukosis as EBL, calf type B-cell lymphoma, juvenile T-cell lymphoma and skin type T-cell lymphoma.

Expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor on B-1a cell from persistent lymphocytosis (PL) cows and lymphoma cell induced by bovine leukemia virus

The effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on B lymphocytes from persistent lymphocytosis (PL) cattle and lymphoma cells induced by bovine leukemia virus (BLV) was studied in vitro. Flow cytometric analysis showed that high levels of receptors to GM-CSF were expressed on these cell types. Proliferation of these B cells was induced in response to bovine GM-CSF. In tumor cell lines, the rate of cell proliferation was correlated with expression of GM-CSF receptors. A monoclonal antibody to GM-CSF inhibited lymphocyte proliferation and blocked the GM-CSF binding of lymphocytes. Cells expressing GM-CSF receptor were Ig positive and both CD5 and CD11 positive (B-1a cell). These results suggest that an abnormal expression of GM-CSF receptors on B lymphocytes from PL and lymphoma cells induced by BLV plays important roles in the PL and proliferation of lymphoma.

Altered response to and production of TGF-beta by B cells from autoimmune NZB mice

New Zealand Black (NZB) mice spontaneously develop immune dysfunction manifested as autoimmune hemolytic anemia and systemic lupus erythematosus. In later life, a subset of these mice develop clonal CD5+ B cell tumors analogous to human chronic lymphocytic leukemia (CLL). NZB disease is marked by B cell hyperactivity characterized by spontaneous immunoglobulin secretion and proliferation. Elimination of autoreactive lymphocytes by apoptosis is a vital mechanism to prevent expansion of self-reactive lymphocyte population. TGF-beta appears to be an important factor in normal and abnormal immune regulation and this cytokine may play a role in the development of chronic human B cell tumors. We asked whether the response to or production of TGF-beta by NZB B cells was aberrant and could contribute to disease development. In this study, we demonstrated that the apoptotic response to TGF-beta was increased in B cells from NZB mice compared to B cells from normal BALB/c mice. The increased apoptosis was related to endogenous activation and was possibly mediated through increased expression of the TGF-beta Type II receptor. Despite functional differences between CD5-negative B cells and CD5-positive B cells, TGF-beta induced apoptosis in both populations to a similar extent. NZB B cells also secrete increased active TGF-beta compared to BALB/c B cells. We suggest that the aberrant secretion of active TGF-beta and the increased response to the apoptotic effects of TGF-beta by NZB B cells may play a role in the disease process of these mice, perhaps attempting to limit the autoimmune phenomena, but possibly also contributing to generalized immunosuppression. We also suggest that the CD5(+) tumors in the NZB mouse may not be a fully appropriate model of human CLL, since CLL B cells are abnormally resistant to the apoptotic effects of TGF-beta.

B-1a, B-1b and conventional B cell lymphoma from enzootic bovine leukosis

In order to characterize the phenotypes of tumor cells and to clarify from which B cell lineage the lymphomas were derived, ten cows with enzootic bovine leukosis were examined by means of immunohistologic staining and flow cytometry. The tumor cells expressed mainly major histocompatibility complex (MHC) class II+ (10/10), BoCD11b+ (9/10), IgG1+ (8/10), B-B2+ (8/10) BoCD5+ (7/10), and lambda light chain+ (7/10). Tumor cells from only one animal expressed sIgM+ (1/10). Tumor cells from all ten animals were negative for IgG2, BoCD3, BoCD4, BoCD8, WC1-N2, and IL-2R alpha. The phenotypes of these tumor cells were all slightly different, suggesting that bovine leukemia virus (BLV)-induced lymphoma expresses phenotypic diversity. Moreover, tumor cells from seven cattle coexpressed BoCD5 and BoCD11b (B-1a cells). On the other hand, tumor cells from two of them only expressed BoCD11b (B-1b cells), and those from one were negative for both BoCD5 and BoCD11b (conventional B cells). Therefore, we concluded that BLV-induced lymphoma cells can be derived from B-1a, B-1b and conventional B cells.

Requirement for increased IL-10 in the development of B-1 lymphoproliferative disease in a murine model of CLL

Malignant B-1 cells derived from NZB mice, a murine model of spontaneous autoimmunity and B cell lymphoproliferative disease, produce significantly higher levels of IL-10 mRNA than normal B-1 or B cells. IL-10 may act as an autocrine growth factor for the expansion of malignant B-1 cells. In order to determine if elevated endogenous production of IL-10 was a required element for the malignant transformation of B-1 cells in NZB mice, backcross animals were studied for the linkage between elevated IL-10 expression and the presence of lymphoid malignancy. The phenotypes of aged (NZB x DBA/2)F1 x NZB animals were determined and a strong correlation was found between the elevated levels of IL-10 mRNA and the development of B-1 malignant clones. In contrast, an increased level of IL-10 message was not associated with elevated serum IgM or the presence of anemia or reticulocytosis which is mainly seen in response to autoantibody production. These results indicate that, at least in NZB, the autoimmunity and lymphoproliferation phenotypes are not linked genetically. IL-10 may enhance proliferation and the development of B-1 cell malignancy rather than antibody production by the B-1 cell subpopulation. Thus, IL-10 plays an important role in B-1 malignancies, and downregulation of IL-10 could be a likely site for intervention in B cell malignancies.

Differential involvement of Th1 and Th2 cytokines in autoimmune diseases

By virtue of their functional antagonism, Th1 cells or cells producing the same cytokines as Th1 cells may behave as "suppressor cells' with respect to Th2 cells and vice versa. An excessive Th1- or Th2-like response may favor the development of different autoimmune diseases. As can be expected from their physiological role, Th-1 cytokines participate in autoimmune diseases with a preferential delayed type hypersensitivity component, i.e. in those diseases in which cytotoxic T cells attack organ-specific target cells. Autoimmune diseases with a predominant Th1 component include experimental autoimmune encephalitis and insulin-dependent diabetes mellitus. In contrast, Th2-type responses participate in systemic autoimmune diseases with a strong humoral component. Such diseases probably include certain drug-induced states of autoaggression, namely mercury-induced autoimmune disease and chlorpromazine-induced autoimmunity. It is tempting to speculate that therapeutic interventions designed to recover a normal Th1/Th2 balance will provide a useful etiological strategy for the re-establishment of self-tolerance.

Altered calcium signal transduction in B-1 malignant cells

Lymphocyte proliferation is guided by receptor-mediated signal transduction pathways that dictate the immunological response/clonality of that cell. We have previously reported that NZB-derived malignant B-1 cells, which serve as a murine model for human chronic lymphocytic leukaemia, demonstrate altered expression of surface IgM and CD45 signalling molecules, and a failure to proliferate following membrane IgM stimulation. To examine receptor-mediated cytosolic calcium (Cai) signalling in B cell leukaemia, we studied IgM-induced Cai responses in malignant B-1 cells and B cells from non-leukaemic mice. Basal Cai was slightly lower in malignant B-1 cells than in non-leukaemic cells. Anti-IgM stimulation induced a sustained increase in Cai to levels 1.3-fold greater than basal Cai in conventional B cells. In contrast, leukaemic B-1 cells demonstrated a sharp but transient rise in Cai followed by a gradual increase to levels 2.3-fold greater than basal [Ca]i Ca influx from extracellular sources contributed to the early and late Cai signal in both sets of cells. Pre-incubation (2-30 min) with anti-CD45 had no effect on basal Cai or the anti-IgM Cai signal in B cells, but reduced the Cai transient in malignant B-1 cells. Additional experiments characterized the effects of phosphorylation/dephosphorylation events on the Cai profile following anti-IgM stimulation. Protein tyrosine kinase inhibitors decreased the anti-IgM-induced Cai transient in malignant B-1 cells by 80%, but only moderately affected (40%) of the Cai response in non-leukaemic B cells. Protein tyrosine phosphatase inhibitors and protein kinase C (PKC) activators attenuated the Cai response to the same degree in normal and leukaemic B cells. These results show that Cai signalling differs widely between non-malignant B cells and malignant B-1 cells, and that tyrosine phosphorylation and CD45 modulation of IgM signalling are involved in the altered Cai responses in malignant B-1 cells.

CD5 expression on B cells may be an activation marker for secretion of anti-myelin antibodies in patients with polyneuropathy associated with monoclonal gammopathy

B cells expressing the CD5 marker belong to a subpopulation with potential autoreactive properties. Increased proportions of CD5+ B cells have been reported in autoimmune diseases. In patients with monoclonal gammopathy and demyelinating polyneuropathy, the M-component often consists of autoantibodies reacting with myelin components. We therefore investigated if CD5+ B cells were involved in the production of anti-myelin antibodies. There was no difference of mean value of CD5+ B cells between patients and controls. However, the proportion of CD5+ B cells was significantly correlated with the amount of anti-myelin antibodies. In seven patients, CD5+ B cells were enriched using an immunomagnetic technique. The number of CD5+ and CD5- B cells secreting anti-myelin antibodies was determined by ELISPOT. In two patients with high levels of antibodies, antibody-secreting cells were mainly, but not exclusively, CD5+ B cells. In five patients with low levels of antibodies, most cells secreting anti-myelin antibodies were CD5-. We conclude that CD5 expressed on B cells may be an activation marker, reflecting B cells producing high amounts of anti-myelin antibodies in patients with polyneuropathy associated with monoclonal gammopathy.