Developmental switches in chemokine response profiles during B cell differentiation and maturation

Differential regulation of IgG anti-capsular polysaccharide and antiprotein responses to intact Streptococcus pneumoniae in the presence of cognate CD4+ T cell help

The relative lack of memory for IgG antipolysaccharide responses is believed to be secondary to the inability of polysaccharides to associate with MHC class II molecules and thus a failure to recruit cognate CD4+ T cell help. However, little is known concerning the role of T cells and the generation of memory for antipolysaccharide Ig responses to intact extracellular bacteria. We used heat-killed, intact Streptococcus pneumoniae, capsular type 14 (Pn14), to evaluate the IgM and IgG responses specific for the capsular polysaccharide (PPS14), the phosphorylcholine determinant of the cell wall C-polysaccharide, and the cell wall protein, pneumococcal surface protein A (PspA). We demonstrate that the IgG (but not IgM), anti-PPS14, and anti-PspA responses to Pn14 are CD4+ T cell dependent and TCR specific. Nevertheless, in contrast to the anti-PspA response, the IgG anti-PPS14 response shows no apparent memory, an accelerated kinetics of primary Ig induction, and a more rapid delivery of CD4+ T cell help. In contrast, the IgG anti-phosphorylcholine response, although also dependent on CD4+ T cells, is TCR nonspecific. We make similar observations using soluble conjugates of PPS14-PspA and C-polysaccharide-PspA. These data lead us to suggest that the central issue concerning the mechanisms underlying different functional outcomes for anti-bacterial IgG responses to capsular polysaccharide vs protein Ags is not necessarily based on the ability to recruit cognate CD4+ T cell help, but perhaps on the nature of the B cell Ag receptor signaling that occurs and/or on the responding B cell subpopulations.

Leukocyte circulation: one-way or round-trip? Lessons from primary immunodeficiency patients

The identification of chemokines has profoundly changed the way we interpret the immune response, elucidating the mechanism by which inflammatory cells are recruited to the site of infection by local secretion of chemoattractants such as CXC chemokine ligand 8 (CXCL8)/interleukin-8, chemokine ligand 2 (CCL2)/monocyte chemoattractant protein 1. This novel view of the immune response has been remodeled further following observations that lymphoid tissue development derives from the coordinated secretion of homeostatic chemokines such as CCL19, CCL21, and CXCL13, which mediate recruitment and clustering of the cells involved in lymphoid organogenesis. The study of primary immunodeficiencies has demonstrated that the number of circulating leukocytes is dependent on migration amongst bone marrow, blood circulation, and inflamed tissues. Defects of leukocyte adhesion and chemotaxis as a result of mutations of beta2-integrins lead to abnormal leukocytosis and susceptibility to skin infections, as observed in leukocyte adhesion deficiency. Conversely, neutropenia in children with myelokathexis is a result of leukocyte retention in the bone marrow because of the mutations of CXC chemokine receptor 4, which affect the capacity of cells to recirculate between blood and bone marrow. Moreover, the identification of the genetic basis of primary immunodeficiencies has shown that many primary immunodeficiencies such as Wiskott-Aldrich syndrome and common variable immunodeficiencies are characterized by altered migration of leukocytes and/or disregulation of cellular response to chemokines. This paper will be focused on the interpretation of primary immunodeficiencies as defects in leukocyte circulation between blood and primary and secondary organs.

Expression of CCL28 by Reed-Sternberg cells defines a major subtype of classical Hodgkin's disease with frequent infiltration of eosinophils and/or plasma cells

Classical Hodgkin's disease (HD) is characterized by rare neoplastic Hodgkin and Reed-Sternberg (H-RS) cells within abundant reactive cellular backgrounds. In most cases, H-RS cells originate from the B-cell lineage, but their immunophenotypes are unusual. Here we newly found frequent expression of chemokine receptors CXCR6 and CCR10 and their respective ligands CXCL16 and CCL28 in HD-derived cell lines. CCR10 is known to be selectively expressed by plasma cells, whereas CCL28 attracts eosinophils via CCR3 and plasma cells via CCR10 and CCR3. Therefore, we examined their expression in HD tissues by immunohistochemistry. We found that H-RS cells in 15 of 19 cases were positive for CCL28. Among them, seven cases were also positive for CCR10, suggesting a potential autocrine effect. In situ hybridization confirmed the expression of CCL28 mRNA in H-RS cells. The CCL28 positivity in H-RS cells did not significantly correlate with that of LMP-1, CCL17, CCL22, or CCL11. However, it significantly correlated with the background accumulation of eosinophils, plasma cells, and CCR10+ cells. Thus, the production of CCL28 by H-RS cells may play a major role in tissue accumulation of eosinophils and/or plasma cells in classical HD. The frequent expression of CCR10 in H-RS cells themselves also supports their close relationship to plasma cells.

Altered leukocyte response to CXCL12 in patients with warts hypogammaglobulinemia, infections, myelokathexis (WHIM) syndrome

The chemokine receptor CXCR4 and its functional ligand, CXCL12, are essential regulators of development and homeostasis of hematopoietic and lymphoid organs. Heterozygous truncating mutations in the CXCR4 intracellular tail cause a rare genetic disease known as WHIM syndrome (warts, hypogammaglobulinemia, infections, myelokathexis), whose pathophysiology remains unclear. We report CXCR4 function in 3 patients with WHIM syndrome carrying heterozygous truncating mutations of CXCR4. We show that CXCR4 gene mutations in WHIM patients do not affect cell surface expression of the chemokine receptor and its internalization upon stimulation with CXCL12. Moreover, no significant differences in calcium mobilization in response to CXCL12 are found. However, the chemotactic response of both polymorphonuclear cells and T lymphocytes in response to CXCL12 is increased. Furthermore, immunophenotypic analysis of circulating T and B lymphocytes reveals a decreased number of memory B cells and of naive T cells and an accumulation of effector memory T cells associated with a restricted T-cell repertoire. Based on our results, we suggest that the altered leukocyte response to CXCL12 may account for the pathologic retention of mature polymorphonuclear cells in the bone marrow (myelokathexis) and for an altered lymphocyte trafficking, which may cause the immunophenotyping abnormalities observed in WHIM patients.

Expression of the chemokine receptors CXCR4 and CCR7 and disease progression in B-cell chronic lymphocytic leukemia/ small lymphocytic lymphoma

OBJECTIVE

To assess the clinical relevance of chemokine receptor expression on the progression of B-cell chronic lymphocytic leukemia (B-CLL).

PATIENTS AND METHODS

Peripheral blood mononuclear cells from 45 patients with B-CLL were purified and compared with lymph node samples collected from 17 of these patients. Also compared were B cells obtained from peripheral blood samples from 5 healthy controls and B cells from reactive lymph nodes from 3 otherwise healthy persons. The patients were treated at the Mayo Clinic in Rochester, Minn, between January 15,1991, and February 7, 2003. Mononuclear cells were stained by a 2-color (fluorescein isothiocyanate/phycoerythrin) flow cytometric assay using antibodies to the chemokine receptors (CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CCR2, CCR4, CCR5, CCR6, and CCR7) and also to CD19.

RESULTS

Of the 45 patients in this study, 20 had Rai stage 0 disease, 12 had stage I disease, 3 had stage II disease, 2 had stage III disease, and 8 had stage IV disease. The mean fluorescent intensity (MFI) of the chemokine receptor expression on B-CLL cells was compared with normal controls and was not significantly different, except for an increase in the median expression of CXCR3 (P = .003) and CCR7 (P = .001) on B-CLL cells. We also found a significant increase in the expression of CXCR4 and CCR7 in B-CLL cells from patients with stage IV compared with stage 0 disease (P = .001 and P = .02, respectively). Furthermore, circulating B-CLL cells showed significantly higher expression of CXCR4 and CCR7 when compared with B lymphocytes in lymph nodes (P = .003 and P < .001, respectively).

CONCLUSION

The expression of CXCR4 and CCR7 on B-CLL cells correlates with Rai stage. Also, these chemokine receptors may be down-regulated once malignant B cells enter the lymph nodes. To our knowledge, this is the first published report that shows the strong association of Rai stage with CXCR4 and CCR7 expression levels in B-CLL cells.

In vivo expression of interleukin-8, and regulated on activation, normal, T-cell expressed, and secreted, by human germinal centre B lymphocytes

T-cell homing within germinal centres (GCs) is required for humoral B-cell responses. However, the mechanisms implicated in the recruitment of T cells into the GC are not completely understood. Here we show, by immunohistology, and Northern and Western blots, that in vivo human GC B lymphocytes can express CxC and CC chemokines. Moreover, B-cell subset-specific experiments reveal that interleukin (IL)-8 and regulated on activation, normal, T-cell expressed, and secreted (RANTES) are predominantly expressed by GC centroblast and centrocytes, suggesting that chemokine expression is essential at stages in which B-lymphocytes engage in active antigen-dependent interactions with T lymphocytes. In keeping with this hypothesis, we show that the T cells recruited into the GC correlatively express the receptors for IL-8 and RANTES. We propose that chemokine expression is a key B-cell function that facilitates T-lymphocyte recruitment into the GCs and supports cognate B-cell : T-cell encounters. Moreover, our data are consistent with the impaired homing of T cells to secondary lymphoid organs in mice that are either deficient in CC and CxC chemokines or their receptors.

Naturally occurring B-cell responses to breast cancer

As demonstrated by the effectiveness of trastuzumab, antibodies against breast cancer antigens are a potentially potent mechanism of tumor control. While trastuzumab is administered exogenously, its efficacy suggests that induction of very high titer antibody responses in vivo might also be therapeutic. Both naturally occurring and vaccine-induced antibody responses to some breast cancer antigens are associated with improved survival in some cases. However, the improvement in survival associated with antibody responses to breast cancer is modest, and tumor regression is not known to be associated with the natural antitumor antibody response, indicating a need for improved understanding of the natural antitumor antibody response. Naturally occurring B-cell responses in the form of serum antibody, tumor reactive lymph node B cells, and tumor-infiltrating B cells have been described, and a variety of breast tumor-associated antigens have been identified based on reactivity of patient antibodies. This review discusses current knowledge of humoral immunity to breast cancer with regard to specific antigens and the basis for their immunogenicity, and the contexts (tumor, lymph node, serum) in which responses are observed. With few exceptions, "tumor-associated antigens" identified with naturally occurring antibodies may be overexpressed on tumor but are in fact nonspecific autoantigens. This suggests that while overexpression or aberrant processing can increase immunogenicity in some cases, the immunogenicity of many or even most tumor-associated antigens is a function of expression in tumor or the result of ancillary tumor factors.

Plasma-cell homing

Recent studies indicate that chemoattractant cytokines (chemokines), together with tissue-specific adhesion molecules, coordinate the migration of antibody-secreting cells (ASCs) from their sites of antigen-driven differentiation in lymphoid tissues to target effector tissues. Developing ASCs downregulate the expression of receptors for lymphoid tissue chemokines and selectively upregulate the expression of chemokine receptors that might target the migration of IgA ASCs to mucosal surfaces, IgG ASCs to sites of tissue inflammation and both types of ASC to the bone marrow - an important site for serum antibody production. By directing plasma-cell homing, chemokines might help to determine the character and efficiency of mucosal, inflammatory and systemic antibody responses.

CC chemokine ligand 20 partially controls adhesion of naive B cells to activated endothelial cells under shear stress

Chemokines are thought to control lymphocyte recruitment to the inflamed endothelium. To dissect chemokine-mediated adhesion, binding of ex vivo isolated splenocytes to tumor necrosis factor (TNF)-activated endothelial cells was analyzed under shear stress. We observed specific adhesion of naive follicular B cells, which could be blocked by pertussis toxin. This indicated a G protein-mediated binding and pointed at a contribution of chemokine receptors to B-cell adhesion. Analysis of chemokines expressed by TNF-activated endothelial cells showed that CC chemokine ligand 2 (CCL2), CCL17, and CCL20 were up-regulated. Only on follicular B cells was the cognate receptor for CCL20, CC chemokine receptor 6 (CCR6), expressed strongly, and a functional transmigration assay with CCR6-negative B cells demonstrated conclusively the sole signaling of CCL20 through CCR6. Desensitization of CCR6 on naive B cells with CCL20 resulted in receptor down-regulation and reduced B-cell adhesion. We conclude that CCL20 plays a vital role in B-cell adhesion to the inflamed endothelium.

Chemokines in the systemic organization of immunity

Directed cellular migrations underlie immune system organization. Chemokines and their receptors (along with surface-adhesion molecules) are central to these migrations, targeting developing and mature leukocytes to tissues and microenvironments suitable for their differentiation and function. The chemokine CXCL12 and its receptor CXCR4 play a central role in the migration of hematopoietic stem cells, and several chemokine receptors are transiently expressed during distinct stages of B- and T-cell development. In the periphery, mature naïve B and T cells utilize the receptors CCR7, CXCR4, and CXCR5 to recirculate through specialized microenvironments within the secondary lymphoid tissues, while effector and memory lymphocytes express bewildering patterns of adhesion molecules and chemokine receptors that allow them to function within microenvironments and non-lymphoid tissues inaccessible to naïve cells. Here, we summarize the role of chemokines and their receptors in the spatial organization of the immune system and consider the implications for immune function.

Chemokines as organizers of primary and secondary lymphoid organs

Lymphoid organs represent highly specialized tissues enabling the development and activation of B and T lymphocytes. Contact between lymphoid and parenchymal cells in bone marrow and thymus is a prerequisite for proper development of B and T cells, respectively, while secondary lymphoid organs, such as spleen and lymph nodes are the places where B and T cells get into contact with antigen presenting cells in order to initiate an adaptive immune response. Recent evidence suggests that few constitutively produced chemokines are essentially required to allow for the correct positioning and interaction of lymphoid and non-lymphoid cells thus creating microenvironments for efficient development and activation of the immune system at multiple stages.

Lymphoid precursors in intestinal cryptopatches express CCR6 and undergo dysregulated development in the absence of CCR6

Small intestinal cryptopatches (CP) are the major anatomic site for extrathymic differentiation by precursors destined to become intestinal intraepithelial T lymphocytes (IEL). We found that mice deficient in CCR6 exhibited a 2.7-fold increase in the number of alphabeta TCR IEL, but little or no expansion of gammadelta TCR IEL. Among the alphabeta TCR IEL subsets, the CD4- CD8alphaalpha+ and CD4+ CD8alphaalpha+ subsets were preferentially expanded in CCR6 null mice. Because some CD8alphaalpha+ IEL can arise through extrathymic differentiation in CP, we investigated CCR6 expression by T lymphocyte precursors undergoing extrathymic differentiation in intestinal CP. In sections of CP, 50-60% of c-kit+ precursors were CCR6+. CD11c(+) cells concentrated at the periphery of CP did not express CCR6. A subset of c-kit+, Lin- cells in lamina propria suspensions was CCR6+, but CCR6 was absent from c-kit+ precursors in bone marrow. CCR6 was absent from the vast majority of mature IEL. CCR6 is present on lymphocyte precursors in cryptopatches, expressed transiently during extrathymic IEL development, and is required for homeostatic regulation of intestinal IEL.

CCR3 expression induced by IL-2 and IL-4 functioning as a death receptor for B cells

We report that CCR3 is not expressed on freshly isolated peripheral and germinal B cells, but is up-regulated after stimulation with IL-2 and IL-4 (approximately 98% CCR3(+)). Ligation of CCR3 by eotaxin/chemokine ligand (CCL) 11 induces apoptosis in IL-2- and IL-4-stimulated primary CD19(+) (approximately 40% apoptotic cells) B cell cultures as well as B cell lines, but has no effect on chemotaxis or cell adhesion. Freshly isolated B cells express low levels of CD95 and CD95 ligand (CD95L) (19 and 21%, respectively). Expression is up-regulated on culture in the presence of a combination of IL-2, IL-4, and eotaxin/CCL11 (88% CD95 and 84% CD95L). We therefore propose that ligation of such newly induced CCR3 on peripheral and germinal B cells by eotaxin/CCL11 leads to the enhanced levels of CD95 and CD95L expression. Ligation of CD95 by its CD95L expressed on neigboring B cells triggers relevant death signaling pathways, which include an increase in levels of Bcl-2 expression, its functional activity, and the release of cytochrome c from the mitochondria into the cytosol. These events initiate a cascade of enzymatic processes of the caspase family, culminating in programmed cell death. Interaction between CCR3 and eotaxin/CCL11 may, besides promoting allergic reactions, drive activated B cells to apoptosis, thereby reducing levels of Ig production, including IgE, and consequently limit the development of the humoral immune response. The apoptotic action of eotaxin/CCL11 suggests a therapeutic modality in the treatment of B cell lymphoma.

The rise and fall of long-lived humoral immunity: terminal differentiation of plasma cells in health and disease

Long-lived humoral immune responses are a hallmark of thymus-dependent immunity. The cellular basis for enduring antibody-mediated immunity is long-lived memory B cells and plasma cells (PCs). Both of these cell populations acquire longevity as a result of antigen-specific, CD40-dependent, cognate interactions with helper T cells within germinal centers (GCs). At the molecular level, defined functional domains of CD40 control the post-GC fate of B cells. PC precursors that emerge from these GC reactions are highly proliferative and terminally differentiate to end-stage cells within the bone marrow (BM). The striking phenotypic similarities between the PC precursors and the putative malignant cell in multiple myeloma (MM) suggests that MM may result from the transformation of PC precursors. Within the domain of autoimmune disease, recent studies have shown that dysregulated migration of PCs to the BM may impact immune homeostasis and the development of lupus. Understanding the processes of normal PC differentiation will provide strategic insights into identifying therapeutic targets for the treatment of differentiated B-cell disorders.

Homing of antibody secreting cells

As activated B cells differentiate into plasma cells they complete a final series of migration steps that take them to locations where they can efficiently carry out their effector function, secreting immunoglobulin (Ig) M or IgG into circulation or releasing dimeric IgA adjacent to the epithelium for transcytosis. Recent experiments have established a key role for chemokines in directing antibody secreting cell (ASC) movement within the secondary lymphoid organs where they are generated, as well as in guiding the cells to the bone marrow or mucosal surfaces. This review discusses the chemokines involved in directing ASC movements, particularly focusing on the role of CXCR4 and CXCL12/SDF1. The function of CCR9 and CCR10 in IgA ASC homing and contributions made by integrins and lectins are also discussed.

A common mucosal chemokine (mucosae-associated epithelial chemokine/CCL28) selectively attracts IgA plasmablasts

IgA immunoblasts can seed both intestinal and nonintestinal mucosal sites following localized mucosal immunization, an observation that has led to the concept of a common mucosal immune system. In this study, we demonstrate that the mucosae-associated epithelial chemokine, MEC (CCL28), which is expressed by epithelia in diverse mucosal tissues, is selectively chemotactic for IgA Ab-secreting cells (ASC): MEC attracts IgA- but not IgG- or IgM-producing ASC from both intestinal and nonintestinal lymphoid and effector tissues, including the intestines, lungs, and lymph nodes draining the bronchopulmonary tree and oral cavity. In contrast, the small intestinal chemokine, TECK (CCL25), attracts an overlapping subpopulation of IgA ASC concentrated in the small intestines and its draining lymphoid tissues. Surprisingly, T cells from mucosal sites fail to respond to MEC. These findings suggest a broad and unifying role for MEC in the physiology of the mucosal IgA immune system.

Role of the chemokine stromal cell-derived factor 1 in autoantibody production and nephritis in murine lupus

In normal mice, stromal cell-derived factor 1 (SDF-1/CXCL12) promotes the migration, proliferation, and survival of peritoneal B1a (PerB1a) lymphocytes. Because these cells express a self-reactive repertoire and are expanded in New Zealand Black/New Zealand White (NZB/W) mice, we tested their response to SDF-1 in such mice. PerB1a lymphocytes from NZB/W mice were exceedingly sensitive to SDF-1. This greater sensitivity was due to the NZB genetic background, it was not observed for other B lymphocyte subpopulations, and it was modulated by IL-10. SDF-1 was produced constitutively in the peritoneal cavity and in the spleen. It was also produced by podocytes in the glomeruli of NZB/W mice with nephritis. The administration of antagonists of either SDF-1 or IL-10 early in life prevented the development of autoantibodies, nephritis, and death in NZB/W mice. Initiation of anti-SDF-1 mAb treatment later in life, in mice with established nephritis, inhibited autoantibody production, abolished proteinuria and Ig deposition, and reversed morphological changes in the kidneys. This treatment also counteracted B1a lymphocyte expansion and T lymphocyte activation. Therefore, PerB1a lymphocytes are abnormally sensitive to the combined action of SDF-1 and IL-10 in NZB/W mice, and SDF-1 is key in the development of autoimmunity in this murine model of lupus.

B cell developmental requirement for the G alpha i2 gene

Null mutation of the Galphai2 trimeric G protein results in a discrete and profound mucosal disorder, including inflammatory bowel disease (IBD), attenuation of IL-10 expression, and immune function polarized to Th1 activity. Genetic and adoptive transfer experiments have established a role for B cells and IL-10 in mucosal immunologic homeostasis and IBD resistance. In this study, we addressed the hypothesis that Galphai2 is required for the development of IL-10-producing B cells. Galphai2(-/-) mice were reduced in the relative abundance of marginal zone (MZ), transitional type 2 (T2), and B-1a B cells and significantly increased in follicular mature and B-1b B cells. Reconstitution of RAG2(-/-) mice with Galphai2(-/-) bone marrow induced an IBD-like colitis and a deficiency in absolute numbers of MZ, T2, and B-1 B cells. Thus, the Galphai2(-/-) genotype in colitis susceptibility and B cell development involved a cis effect within the hemopoietic compartment. In vitro, the B cell population of Galphai2(-/-) mice was functionally deficient in LPS-induced proliferation and IL-10 production, consistent with the exclusive capacity of T2 and MZ cell subpopulations for LPS responsiveness. In vivo, Galphai2(-/-) mice were selectively impaired for the IgM response to T-independent type II, consistent with the relative depletion of MZ and peritoneal B-1 subpopulations. Collectively, these results reveal a selective role for Galphai2 in MZ and B-1 B cell development. Disorders of this Galphai2-dependent process in B cell development may represent a mechanism for IBD susceptibility.

Cutting edge: profile of chemokine receptor expression on human plasma cells accounts for their efficient recruitment to target tissues

We systematically examined the repertoire of chemokine receptors expressed by human plasma cells. Fresh bone marrow plasma cells and myeloma cells consistently expressed CXCR4, CXCR6, CCR10, and CCR3. Accordingly, plasma cells responded to their respective ligands in chemotaxis and very late Ag-4-dependent cell adhesion to fibronectin. Immobilized CXC chemokine ligand (CXCL)16, a novel transmembrane-type chemokine and CXCR6 ligand, also directly induced adhesion of plasma cells without requiring G(alpha i) signaling or divalent cations. Furthermore, we revealed consistent expression of CXCL12 (CXCR4 ligand), CXCL16 (CXCR6 ligand), and CC chemokine ligand 28 (CCR10 and CCR3 ligand) in tissues enriched with plasma cells including bone marrow, and constitutive expression of CXCL12, CXCL16, and CC chemokine ligand 28 by cultured human bone marrow stromal cells. Collectively, plasma cells are likely to be recruited to bone marrow and other target tissues via CXCR4, CXCR6, CCR10, and CCR3. CXCR6 may also contribute to tissue localization of plasma cells through its direct binding to membrane-anchored CXCL16.

Expression of chemokine receptors, CXCR4 and CXCR5, and chemokines, BLC and SDF-1, in the eyes of patients with primary intraocular lymphoma

OBJECTIVE

Chemokines have a range of biologic activities, including regulation of leukocyte trafficking, modulation of hematopoietic cell proliferation, and adhesion to extracellular matrix molecules. Specifically, B-lymphocyte chemoattractant (BLC); BCA-1; CXCL13, SCYB13) and stromal cell-derived factor-1 (SDF-1, CXCL12, SCYB12) are chemotactic for human B cells, and their ligands CXCR4 and CXCR5 are differentially expressed on B cells, including malignant B cells. We investigated the expression of these chemokine/chemokine receptors in eyes with primary intraocular B-cell lymphoma (PIOL).

DESIGN

Observational case series (human tissue study).

METHODS

Three freshly enucleated eyes with PIOL and a normal autopsied eye were frozen and sectioned. The sections were evaluated using immunohistochemistry (avidin-biotin-complex immunoperoxidase technique) for CXCR4, CXCR5, BLC, and SDF-1 to detect the expression and location. Reverse transcriptase-polymerase chain reaction was used to detect chemokine transcripts of CXCR4, CXCR5, BLC, and SDF-1 in PIOL and retinal pigment epithelium (RPE) cells after microdissection-either by laser capture (Arcturus) or by manual dissection-from frozen sections.

MAIN OUTCOME MEASURES AND RESULTS

The three PIOL eyes showed similar pathology, with typical diffuse large B-lymphoma cells subjacent to the RPE. The eyes also demonstrated a similar chemokine profile. High expression levels of CXCR4 and CXCR5 were found limited to the lymphoma cells. In contrast, BLC protein was expressed in the RPE but not located in other ocular resident cells. SDF-1 was barely detected in a few RPE cells. CXCR4 and CXCR5 transcripts were detected abundantly in lymphoma cells, whereas BLC and SDF-1 transcripts were detected only in the RPE and not the malignant cells. No chemokine expression was detected on the RPE cells in the normal control eye.

CONCLUSIONS

Chemokines and chemokine receptors selective for B cells were identified in RPE and malignant B cells, respectively. BLC, and possibly SDF-1, attracts both normal and malignant B-cells while promoting migration of only small numbers of T cells and macrophages. We propose that B-cell chemokines may be involved in the pathogenesis of PIOL by selectively attracting lymphoma cells to the RPE from the choroidal circulation. Our data suggest that inhibition of B-cell chemoattractants could be a future strategy for the treatment of PIOL.

Lymphocyte traffic control by chemokines: follicular B helper T cells

Follicular B helper T (T(FH)) cells make up a CD4(+) memory T cell subset with unique migration properties, defined by the expression of the chemokine receptor CXCR5 and responsiveness to the CXCR5-selective chemokine BCA-1, which is produced in B cell follicles. The generation of T(FH) cells is closely associated with initiation of adaptive immunity. Here, we discuss the relationship of T(FH) cells with those T cells characterized by an inherent secondary lymphoid tissue homing program. Special emphasis is placed on the potential involvement of T(FH) cells in the humoral immune response within B cell follicles, as well as the differentiation potential of these non-polarized cells.

Lymphoid chemokines CCL19 and CCL21 are expressed in the central nervous system during experimental autoimmune encephalomyelitis: implications for the maintenance of chronic neuroinflammation

The simultaneous presence of dendritic, T- and B-cells in the central nervous system (CNS) of mice with experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, suggests that interactions among these cell types might be instrumental in the local induction and maintenance of autoimmune reactions. In this study, we explored the possibility that such aberrant leukocyte recruitment in the CNS could be sustained by "lymphoid" chemokines which orchestrate dendritic cell and lymphocyte homing to lymphoid organs. Transcripts for CCL19 and CCL21 and their common receptor CCR7 were induced in the CNS of mice undergoing relapsing-remitting and chronic-relapsing EAE. While CCL21 immunoreactivity was confined to the endothelium of some inflamed blood vessels, CCL19 was expressed by many infiltrating leukocytes and some astrocytes and microglia in the CNS parenchyma. CCR7+ cells accumulated in inflammatory lesions during EAE progression, when abundant infiltration of the CNS by mature dendritic cells, B-cells and cells expressing naive T-cell markers also occurred. These findings suggest that CCL19 and CCL21 produced in the EAE-affected CNS may be critical for the homing of antigen presenting cells and lymphocytes, resulting in continuous local antigenic stimulation and maintenance of chronic neuroinflammation.

Expression and function of chemokine receptors in human multiple myeloma

Multiple myeloma (MM) is a B cell tumor characterized by its selective localization in the bone marrow. The mechanisms that contribute to the multiple myeloma cell recruitment to the bone marrow microenvironment are not well understood. Chemokines play a central role for lymphocyte trafficking and homing. In this study we have investigated expression and functional importance of chemokine receptors in MM-derived cell lines and primary MM cells. We found that MM cell lines express functional CCR1, CXCR3 and CXCR4 receptors, and some also CCR6. Although only a minority of the cell lines responded by calcium mobilization after agonist stimulation, a migratory response to the CCR1 ligands RANTES and MIP-1 alpha was obtained in 5/6 and 4/6, respectively, of the cell lines tested. Five out of six cell lines showed a response to the CXCR4 ligand SDF-1. In addition, 3/6 cell lines migrated in response to MIP-3 alpha and IP-10, ligands for CCR6 and CXCR3, respectively. The expression of CXCR4 and CCR1 and the migration to their ligands, SDF-1, and RANTES and MIP-1 alpha, respectively, were also demonstrated in primary MM cells. These findings suggest that chemokine receptor expression and the migratory capacity of MM cells to their ligands are relevant for the compartmentalization of MM cells in the bone marrow.

Human osteoblasts express functional CXC chemokine receptors 3 and 5: activation by their ligands, CXCL10 and CXCL13, significantly induces alkaline phosphatase and beta-N-acetylhexosaminidase release

Osteoblasts (OBs) contribute to the maintenance of bone homeostasis and their activity can be influenced by immune cells localized in bone lacunae. We investigated the expression of the chemokine receptors in isolated human OBs by reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry, and report a novel finding, namely, that OBs express high levels of CXC chemokine receptor 3 (CXCR3) and 5 (CXCR5). Functional assays to evaluate CXCR3 and CXCR5 demonstrated that their ligands-CXCL10 and CXCL13, respectively-significantly induce the release of beta-N-acetylhexosaminidase, an enzyme involved in endochondral ossification and bone remodeling able to degrade important extracellular matrix components. Alkaline phosphatase activity, a useful index of matrix formation was also up-regulated by CXCL10 and CXCL13. However, OB activation by these ligands does not affect OB proliferation. Both Bordetella pertussis toxin and neutralizing anti-CXCR3/anti-CXCR5 monoclonal antibodies block CXCL10 and CXCL13 induction, respectively. We also demonstrated the expression of CXCL10 and CXCL13 in human bone tissue biopsies. These results indicate that both CXCR3/CXCL10 and CXCR5/CXCL13 receptor-ligand pairs may play an important role in OB activity through the specific up-regulation of two enzymes, which are involved in the bone remodeling process. Moreover, our data suggest that OBs may play a role in the modulation of bone formation through the combined action of these two enzymes.

BOB.1/OBF.1 deficiency affects marginal-zone B-cell compartment

Marginal-zone (MZ) B cells represent a first line of defense against particulate blood-borne antigens. Together with the B1 cells, they are responsible for the early response against type II T-independent antigens. The molecular pathways controlling the development of MZ B cells are only poorly understood. We found that these cells are virtually absent in mice deficient in the BOB.1/OBF.1 coactivator. Loss of these B cells was demonstrated by the lack of cells showing the appropriate cell surface phenotype but also by histological analyses and tri-nitro-phenol-Ficoll capturing. The lack of these cells is a B-cell-intrinsic defect, as shown by bone marrow complementation experiments. We also show that the expression of BOB.1/OBF.1 in peripheral B cells is required for the development of MZ B lymphocytes. Our analysis of BOB.1/OBF.1-deficient splenic B cells reveals alterations in cell motility, tumor necrosis factor receptor expression, and B-cell receptor (BCR) signaling. These changes could contribute to the loss of MZ B lymphocytes by altering the maturation of the cells. Interestingly, development of and BCR signaling in B1 B cells are completely normal in BOB.1/OBF.1 mutant mice.

Analysis of B cell memory formation using DNA microarrays

DNA microarray analysis of B cell subsets has identified comprehensive programs of gene expression that distinguish B cells at discrete stages of differentiation. The next task is to identify key genetic signals within these complex programs that regulate the dynamic cellular events during B cell activation in vivo. After stimulation with antigen, naïve B cells proliferate and differentiate, and then produce antibodies. Crucial qualitative differences in antibody responses are observed depending on whether or not B cells receive T cell help during activation. Proteins, lipopolysaccharides, and polysaccharides stimulate T-dependent (TD), T-independent type 1 (TI-1), and type 2 (TI-2) antibody responses, respectively. Only TD responses generate somatically mutated antibody-forming (plasma) cells and memory B cells, which produce high affinity anamnestic responses to subsequent antigen challenge. Somatic mutation of immunoglobulin genes occurs during B cell proliferation in germinal centres (GC), which are typical in TD responses but rare in TI responses. However, we have described a model, which is exceptional because numerous large GC form in response to a model TI-2 antigen, (4-hydoxy-3-nitrophenyl) acetyl (NP)-Ficoll. Significantly, these GC undergo involution before memory B cells are generated. This model provides an opportunity to investigate the genetic signals that drive memory cell formation, and we have compared global gene expression in TI and TD GC to identify a relatively small number of genes that are differentially expressed between the two prototypic B cell responses. This model demonstrates how genome-scale technology can be adapted to investigate specific aspects of B cell biology.

A developing picture of lymphopoiesis in bone marrow

The earliest progenitors of lymphocytes are extremely rare and typically present among very complex populations of hematopoietic cells. Additionally, it is difficult to know how cells with any given set of characteristics are developmentally related to stem cells and maturing lymphoid precursors. However, it is now possible to divide bone marrow into progressively smaller fractions and exploit well-defined culture systems to determine which ones contain cells that can turn into lymphocytes. Analysis of steroid hormone sensitive cells and use of two-step cultures is providing additional information about the most likely differentiation pathways for B and natural killer cell lineage lymphocytes. A newly identified category of early lymphoid progenitors can now be sorted to high purity from RAG1/GFP knock in mice. Furthermore, the same experimental model makes it possible to image lymphoid progenitors in fetal and adult hematopoietic tissues.

Immune surveillance and effector functions of CCR10(+) skin homing T cells

Skin homing T cells carry memory for cutaneous Ags and play an important sentinel and effector role in host defense against pathogens that enter via the skin. CCR10 is a chemokine receptor that is preferentially expressed among blood leukocytes by a subset of memory CD4 and CD8 T cells that coexpress the skin-homing receptor cutaneous lymphocyte Ag (CLA), but not the gut-homing receptor alpha(4)beta(7). Homing and chemokine receptor coexpression studies detailed in this study suggest that the CLA(+)/CCR10(+) memory CD4 T cell population contains members that have access to both secondary lymphoid organ and skin compartments; and therefore, can act as both "central" and "effector" memory T cells. Consistent with this effector phenotype, CLA(+)/CCR10(+) memory CD4 T cells from normal donors secrete TNF and IFN-gamma but minimal IL-4 and IL-10 following in vitro stimulation. Interactions of CCR10 and its skin-associated ligand CC ligand 27 may play an important role in facilitating memory T cell entry into cutaneous sites during times of inflammation.

Humoral immunity and long-lived plasma cells

A selected fraction of plasmablasts enters the compartment of nondividing, long-lived plasma cells to maintain humoral antibody memory. In accord with a current model for lymphocyte homeostasis, the lifetime of long-lived plasma cells is probably regulated by competition for a limited number of survival niches present in splenic red pulp, bone marrow and inflamed tissue. Plasma cells secreting autoantibodies specific for some, but not all, self-antigens are probably 'allowed' to enter the compartment of long-lived plasma cells and provide antibody-mediated 'autoimmune memory' that is resistant to conventional therapies.

B lymphocyte stimulator (BLyS): a therapeutic trichotomy for the treatment of B lymphocyte diseases

B Lymphocyte Stimulator (BLyS protein) is a member of the tumor necrosis factor (TNF) family of ligands and functions as an essential in vivo regulator of B lymphocyte homeostasis. As such, changes in systemic BlyS protein expression caused by disruption of the gene encoding BLyS or administration of neutralizing soluble receptors have resulted in profound losses in mature B cell numbers and impaired humoral immunity. A similar phenotype has been observed in A/WySnJ mice that express a truncated BLyS receptor and are thus defective in BLyS signal transduction. In contrast, overexpression of BLyS protein in BLyS-transgenic mice results in B cell hyperplasia, hypergammaglobulinemia, and development of autoimmune-like disease. The ability of BLyS to regulate both the size and repertoire of the peripheral B cell compartment raises the possibility that BLyS and antagonists thereof may form the basis of a therapeutic trichotomy. As an agonist, BLyS protein may enhance humoral immunity in congenital or acquired immunodeficiencies such as those resulting from viral infection or cancer therapy. BLyS-specific antagonists (antibodies or soluble receptors) that inhibit the biological activity of BLyS may be effective therapies for those autoimmune diseases characterized by polyclonal hypergammaglobulinemia and elevated autoantibody titers. Finally, the specificity of BLyS for B-lineage cells raises the possibility that BLyS may be used as a targeting vehicle for delivery of a cytotoxic or cytolytic signal to neoplastic B-lineage cells expressing one or more of the three known BLyS receptors. This review discusses the therapeutic potential of BLyS in the context of BLyS structure, function and receptor specificity.

Abnormal organogenesis of Peyer's patches in mice deficient for NF-kappaB1, NF-kappaB2, and Bcl-3

BACKGROUND & AIMS

Nuclear factor (NF) kappaB1, NF-kappaB2, and Bcl-3 encode for proteins of the NF-kappaB/Rel/IkappaB families, known as regulators of innate and adoptive immune responses. Targeted disruption of these genes showed essential roles in lymphoid organ development and organization.

METHODS

NF-kappaB1-, NF-kappaB2-, and Bcl-3-deficient mouse lines were established, and their role in organogenesis of Peyer's patches (PP) was investigated.

RESULTS

Macroscopic inspection showed a reduced number and size of PP in Bcl-3(-/-) and NF-kappaB1(-/-) mice but failed to detect PP in NF-kappaB2(-/-) mice. Whole-mount in situ hybridization revealed the presence of interleukin-7 receptor-alpha spots in NF-kappaB2(-/-) mice, indicating no defect in PP organogenesis of NF-kappaB2(-/-) mice in principle. Immunostaining shows that residual lymphocytes mainly consist of T cells. B cells are substantially reduced and are accumulated as terminal extravasations. Organized follicular structures and follicular dendritic cell networks fail to form, and myeloid, but not lymphoid, dendritic cells are obviously reduced. Expression of the chemokines macrophage inflammatory protein-3alpha, B-lymphocyte chemoattractant, and thymus-expressed chemokine is impaired in epithelial cells and in the subendothelial dome area that is not well defined. A similar but less severe phenotype is seen in Bcl-3(-/-) mice, which also do not develop germinal centers. In contrast, in NF-kappaB1(-/-) mice, T-cell numbers are visibly reduced, and no alteration could be observed in the B-cell and dendritic-cell populations.

CONCLUSIONS

These data show that all 3 genes are crucial for PP development but contribute differently to PP organogenesis.

Chemokine responses in schistosomal antigen-elicited granuloma formation

Host immune systems have evolved specialized responses to multicellular parasites. This is well represented by the type 2 granulomatous response to Schistosoma mansoni egg antigens, which is an eosinophil-rich inflammatory response mediated by Th2-associated cytokines. Using Ag-bead models of pulmonary granuloma formation in mice, we defined characteristic chemokine (CK) profiles in the granulomatous lungs. Our findings point to a role for C-C chemokine receptor-2 (CCR2) and CCR3 agonists such as monocyte chemotactic proteins (MCPs) 1/CCL2, 3/CCL7 and 5/CCL12 as important participants that are subject to regulation by Th2 cytokines interleukin (IL)-4 and IL-13. CCR4 and CCR8 agonists are also likely contributors. Analysis of CK receptor knockout mice revealed that CCR2 ligands (e.g. MCP-1 and 5) promoted early phase granuloma macrophage accumulation, whereas anti-MCP-3 (CCL7) antibody treatment abrogated eosinophil recruitment. CCR8 knockout mice also demonstrated impaired eosinophil recruitment but this appeared to be related to impaired Th2 cell function. Transcript analysis of CD4+ T cells generated during schistosome granuloma formation failed to show biased CCR8 expression but, having a more limited receptor repertoire, these cells were likely more dependent on CCR8 ligands. Together, these studies indicate an intricate involvement of chemokines in various stages and aspects of schistosomal egg Ag-elicited granuloma formation.

Human B cells become highly responsive to macrophage-inflammatory protein-3 alpha/CC chemokine ligand-20 after cellular activation without changes in CCR6 expression or ligand binding

CCR6 is the only known receptor for the chemokine macrophage-inflammatory protein (MIP)-3alpha/CC chemokine ligand (CCL)20. We have shown previously that CCR6 is expressed on peripheral blood B cells, but CCR6 activity on these cells is low in in vitro assays. We report that MIP-3alpha/CCL20-induced calcium flux and chemotaxis can be enhanced significantly on peripheral blood and tonsillar B cells after activation by cross-linking surface Ag receptors. Of particular interest is the fact that the enhanced activity on B cells was not associated with an increase in CCR6 expression as assessed by levels of receptor mRNA, surface staining, or MIP-3alpha/CCL20 binding sites, or by a change in the affinity of the receptor for ligand. These data convincingly demonstrate that responses to a chemokine can be regulated solely by changes in the downstream pathways for signal transduction resulting from Ag receptor activation, and establish CCR6 as an efficacious receptor on human B cells.

Hematopoietic stem cells are uniquely selective in their migratory response to chemokines

Although hematopoietic stem cell (HSC) migration into and out of sites of active hematopoiesis is poorly understood, it is a critical process that underlies modern clinical stem cell transplantation and may be important for normal hematopoietic homeostasis. Given the established roles of chemotactic cytokine (chemokine)-directed migration of other leukocyte subsets, the migration of murine HSC to a large panel of CC and CXC chemokines was investigated. HSC migrated only in response to stromal derived factor-1alpha, the ligand for the CXC chemokine receptor 4 (CXCR4). CXCR4 expression by HSC was confirmed by reverse transcription polymerase chain reaction analysis. Surprisingly, HSC also expressed mRNA for CCR3 and CCR9, although they failed to migrate to the ligands for these receptors. The sharply restricted chemotactic responsiveness of HSC is unique among leukocytes and may be necessary for the specific homing of circulating HSC to bone marrow, as well as for the maintenance of HSC in hematopoietic microenvironments.

Differential expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in ulcerative colitis and Crohn's disease

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is selectively expressed in the endothelial cells of intestinal mucosa and gut-associated lymphoid tissue (GALT). Engagement of MAdCAM-1 to its ligand, integrin alpha4beta7, on lymphocytes is associated with the homing of gut-associated lymphocytes to normal gastrointestinal tract and inflammation sites. The present study was designed to elucidate differences between Crohn's disease (CrD) and ulcerative colitis (UC) from the expression patterns of MAdCAM-1. Samples were taken from 40 patients with CrD and 24 patients with UC at surgical resection. Using frozen sections, immunohistochemistry was performed for MAdCAM-1, E-selectin and CD34. MAdCAM-1+ venules were abundant in inflamed mucosa in both UC and CrD. In contrast, clear differences were noted between UC and CrD in the inflammatory area in the ulcer base, that is, MAdCAM-1+ venules were more abundant in CrD than in UC (P < 0.001), while E-selectin was expressed equally in these venules in both diseases. Furthermore, CrD was characterized by the occurrence of MAdCAM-1+ venules in deeper layers of the intestinal tissue, mainly in lymphoid aggregates. Our data indicated more extensive expression of MAdCAM-1 in CrD, which could contribute not only to mucosal inflammation, but also to transmural inflammation in CrD.

The chemokine receptor CCR7 and alpha4 integrin are important for migration of chronic lymphocytic leukemia cells into lymph nodes

Malignant lymphocyte migration into lymph nodes is an important aspect of chronic lymphocytic leukemia (CLL), yet little is known about the processes involved. Here we demonstrate that CLL cells migrate across vascular endothelium in response to at least 3 chemokines, namely, CCL21, CCL19, and CXCL12. Moreover, transendothelial cell migration (TEM) in response to CCL21 and CCL19 was significantly higher for the malignant B cells of patients who had clinical lymph node involvement as compared with those of patients lacking such organomegaly. Furthermore, the expression of CCR7, the receptor for both CCL21 and CCL19, correlated with clinical lymphadenopathy, and blocking of CCR7 inhibited CLL cell TEM. By using immunohistochemistry we demonstrated that CCL21 and CCL19, but not CXCL12, are located in high endothelial venules and are, therefore, in an appropriate location to induce TEM. Regarding the adhesion receptors involved in TEM, alpha4 (most likely in association with beta1) and alphaLbeta2 were shown to be important in CLL cell TEM in vitro, but only the level of alpha4 expression correlated with the presence of clinical lymphadenopathy. The present studies are the first to shed light on the factors determining CLL cell entry into nodes and define the phenotype of circulating malignant cells likely to determine the pattern of lymph node enlargement in the disease.

Structure, function, and inhibition of chemokines

Chemokines are the largest family of cytokines in human immunophysiology. These proteins are defined by four invariant cysteines and are categorized based on the sequence around the first two cysteines, which leads to two major and two minor subfamilies. Chemokines function by activating specific G protein-coupled receptors, which results in, among other functions, the migration of inflammatory and noninflammatory cells to the appropriate tissues or compartments within tissues. Some of these proteins and receptors have been implicated or shown to be involved in inflammation, autoimmune diseases, and infection by HIV-1. The three-dimensional structure of each monomer is virtually identical, but the quaternary structure of chemokines is different for each subfamily. Structure-function studies reveal several regions of chemokines to be involved in function, with the N-terminal region playing a dominant role. A number of proteins and small-molecule antagonists have been identified that inhibit chemokine activities. In this review, we discuss aspects of the structure, function, and inhibition of chemokines.

BCR ligation reprograms B cells for migration to the T zone and B-cell follicle sequentially

We have studied the impact of B-cell receptor (BCR) or CD40 ligation on the in vitro chemotactic response of tonsillar B cells to 4 chemokines: stromal cell-derived factor (SDF)-1alpha, macrophage inflammatory protein (MIP)-3alpha, MIP-3beta, and B-cell-attracting chemokine (BCA)-1. In the tonsil, SDF-1 and MIP-3alpha are both expressed in the crypt epithelium, while MIP-3beta is found in the T zone and BCA-1 in the follicles. Resting virgin and memory B cells display a similar chemotaxis pattern, and they both have the potential to migrate in vitro to all 4 chemokines studied. This pattern of responsiveness is strongly modified by a surrogate antigen (Ag) but is not altered by CD40 ligand. We report here that surrogate Ag induces a profound and sustained suppression of the response to the crypt chemokines SDF-1alpha and MIP-3alpha, while it exacerbates the migratory response to MIP-3beta. The effect of surrogate Ag on the response to BCA-1 is biphasic: After an initial phase of suppression, chemotaxis toward BCA-1 is strongly up-regulated. Our results suggest that Ag is primarily responsible for reprogramming the B-cell chemotaxis responsiveness during the humoral response. We propose that it initiates an ordered change of the chemotaxis machinery allowing Ag-activated B cells to relocate in the T zone and B-cell follicles sequentially.

A role for CCR9 in T lymphocyte development and migration

CCR9 mediates chemotaxis in response to CCL25/thymus-expressed chemokine and is selectively expressed on T cells in the thymus and small intestine. To investigate the role of CCR9 in T cell development, the CCR9 gene was disrupted by homologous recombination. B cell development, thymic alphabeta-T cell development, and thymocyte selection appeared unimpaired in adult CCR9-deficient (CCR9(-/-)) mice. However, competitive transplantation experiments revealed that bone marrow from CCR9(-/-) mice was less efficient at repopulating the thymus of lethally irradiated Rag-1(-/-) mice than bone marrow from littermate CCR9(+/+) mice. CCR9(-/-) mice had increased numbers of peripheral gammadelta-T cells but reduced numbers of gammadeltaTCR(+) and CD8alphabeta(+)alphabetaTCR(+) intraepithelial lymphocytes in the small intestine. Thus, CCR9 plays an important, although not indispensable, role in regulating the development and/or migration of both alphabeta(-) and gammadelta(-) T lymphocytes.

Herpes simplex virus selectively induces expression of the CC chemokine RANTES/CCL5 in macrophages through a mechanism dependent on PKR and ICP0

Recruitment of leukocytes is essential for eventual control of virus infections. Macrophages represent a leukocyte population involved in the first line of defense against many infections, including herpes simplex virus (HSV) infection. Through presentation of antigens to T cells and production of cytokines and chemokines, macrophages also constitute an important link between the innate and adaptive immune systems. Here, we have investigated the chemokine expression profile of macrophages after HSV infection and the virus-cell interactions involved. By reverse transcription-PCR and cDNA arrays, we found that HSV type 1 (HSV-1) and HSV-2 induced expression of the CC chemokine RANTES/CCL5 in murine macrophage cell lines and peritoneal cells. The CXC chemokine BCA-1/CXCL13 was also induced in peritoneal cells. Twenty-six other chemokines tested were not affected. Accumulation of RANTES mRNA was detectable after 5 h of infection, was sensitive to UV irradiation of the virus, and was preceded by accumulation of viral immediate-early mRNA and proteins. The viral components responsible for initiation of RANTES expression were examined with virus mutants and RAW 264.7 macrophage-like cells expressing a dominant negative mutant of the double-stranded-RNA-activated protein kinase (PKR). The PKR mutant cell line displayed reduced constitutive and HSV-inducible RANTES expression compared to the control cell line. HSV-1 mutants deficient in genes encoding the immediate-early proteins ICP4, ICP22, and ICP27 remained fully capable of inducing RANTES expression in macrophages. By contrast, the ability of an ICP0-deficient HSV-1 mutant to induce RANTES expression was compromised. Thus, HSV selectively induces expression of RANTES in macrophages through a mechanism dependent on cellular PKR and viral ICP0.

Human B cells immortalized with Epstein-Barr virus upregulate CCR6 and CCR10 and downregulate CXCR4 and CXCR5

Compared to peripheral blood resting B cells, Epstein-Barr virus (EBV)-immortalized B cells consistently express CCR6 and CCR10 at high levels and CXCR4 and CXCR5 at low levels. Accordingly, these cells vigorously responded to the ligands of CCR6 and CCR10 but not to those of CXCR4 and CXCR5. In a human EBV-negative B-cell line, BJAB, stable expression of EBNA2 upregulated CCR6, while stable expression of EBNA2 as well as LMP1 downregulated CXCR4. On the other hand, upregulation of CCR10 or downregulation of CXCR5 was not induced in BJAB by stable expression of EBNA2 or LMP1. Thus, these changes may be due to a plasmablast-like stage of B-cell differentiation fixed by EBV immortalization. EBV-infected B cells in infectious mononucleosis are known to avoid germinal centers and accumulate under the mucosal surfaces. EBV-associated opportunistic lymphomas also tend to occur in extranodal sites. These preferred sites of in vivo localization are consistent with the unique profile of chemokine receptor expression exhibited by EBV-immortalized B cells.

Frequent expression of CCR4 in adult T-cell leukemia and human T-cell leukemia virus type 1-transformed T cells

Chemokines and chemokine receptors play important roles in migration and tissue localization of various lymphocyte subsets. Here, we report the highly frequent expression of CCR4 in adult T-cell leukemia (ATL) and human T-cell leukemia virus type 1 (HTLV-1)-immortalized T cells. Flow cytometric analysis revealed that ATL and HTLV-1-immortalized T-cell lines consistently expressed CCR4. Inducible expression of HTLV-1 transcriptional activator tax in a human T-cell line Jurkat did not, however, up-regulate CCR4 mRNA. In vitro immortalization of peripheral blood T cells led to preferential outgrowth of CD4(+) T cells expressing CCR4. We further demonstrated highly frequent expression of CCR4 in fresh ATL cells by (1) reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of CCR4 expression in peripheral blood mononuclear cells (PBMCs) from patients with ATL and healthy controls; (2) flow cytometric analysis of CCR4-expressing cells in PBMCs from patients with ATL and healthy controls; (3) CCR4 staining of routine blood smears from patients with ATL; and (4) an efficient migration of fresh ATL cells to the CCR4 ligands, TARC/CCL17 and MDC/CCL22, in chemotaxis assays. Furthermore, we detected strong signals for CCR4, TARC, and MDC in ATL skin lesions by RT-PCR. Collectively, most ATL cases have apparently derived from CD4(+) T cells expressing CCR4. It is now known that circulating CCR4(+) T cells are mostly polarized to Th2 and also contain essentially all skin-seeking memory T cells. Thus, HTLV-1-infected CCR4(+) T cells may have growth advantages by deviating host immune responses to Th2. CCR4 expression may also account for frequent infiltration of ATL into tissues such as skin and lymph nodes.

Reduction of marginal zone B cells in CD22-deficient mice

CD22 is a B cell-specific member of the immunoglobulin superfamily and binds to sialic acid. CD22 inhibits B cell receptor signaling. Mice deficient for CD22 show a largely normal B cell development. Here, we have performed a detailed analysis of the splenic B cell population and found that the subset of marginal zone (MZ) B cells was selectively reduced in CD22-deficient mice. CD22-deficient mice showed a lack of TNP-ficoll capturing cells in the MZ and a reduced response to TNP-ficoll, particularly when the antigen was applied intravenously. CD22-deficient B cells showed both enhanced motility as well as enhanced chemotaxis to certain chemokines. The altered chemokine responsiveness or the higher signaling capacity of CD22-deficient B cells may lead to the compromised MZ B cell compartment, as both processes have previously been shown to affect MZ composition.

The intestinal chemokine thymus-expressed chemokine (CCL25) attracts IgA antibody-secreting cells

Immunoglobulin A (IgA) provides protection against pathogens at mucosal surfaces. Chemotactic responses have been hypothesized to target IgA plasma cells involved in mucosal immune responses. We show here that thymus-expressed chemokine (TECK, CCL25) is a potent and selective chemoattractant for IgA antibody-secreting cells (ASC), efficiently recruiting IgA-producing cells from spleen, Peyer's patches, and mesenteric lymph node. Cells secreting IgA antibody in response to rotavirus, an intestinal pathogen, also respond well. In contrast, IgG- and IgM-ASC respond poorly. Epithelial cells in the small intestines, a principal site of IgA-ASC localization and IgA production in the body, highly and selectively express TECK. The migration of IgA-ASC to the intestinal epithelial cell chemokine TECK may help target IgA-producing cells to the gut wall, thus helping define and segregate the intestinal immune response.

Interleukin-10 modulates the sensitivity of peritoneal B lymphocytes to chemokines with opposite effects on stromal cell-derived factor-1 and B-lymphocyte chemoattractant

Interleukin-10 (IL-10) is constitutively produced by peritoneal B1a lymphocytes, and stromal cell-derived factor-1 (SDF-1) by mesothelial cells. Independent studies have shown that both IL-10 and SDF-1 are involved in the persistence of the peritoneal B-lymphocyte compartment. This study shows that IL-10 and SDF-1 act in synergy on peritoneal B lymphocytes. Indeed, autocrine production of IL-10 was absolutely required for all effects of SDF-1 on these cells, including increased proliferation, survival, and chemotaxis. Moreover, adding IL-10 to peritoneal B lymphocytes increased the effects of SDF-1. Neither IL-5, IL-6, nor IL-9 affected the response of peritoneal B lymphocytes to SDF-1. IL-10 was chemokinetic for peritoneal B lymphocytes, increasing their random mobility. It also potentiated the SDF-1-induced reorganization of the cytoskeleton without affecting CXCR4 gene expression by peritoneal B lymphocytes. Despite its chemokinetic properties, IL-10 abolished the migration of peritoneal B lymphocytes in response to B-lymphocyte chemoattractant (BLC), a chemokine targeting B lymphocytes to lymphoid organ follicles. The ability of B1a lymphocytes to produce IL-10 constitutively, combined with the opposite effects of this cytokine on the responses to SDF-1 and BLC, may account for the selective accumulation of B1 lymphocytes in body cavities.

CXCL13 is required for B1 cell homing, natural antibody production, and body cavity immunity

B1 cells are a predominant cell type in body cavities and an important source of natural antibody. Here we report that in mice lacking the chemokine, CXCL13, B1 cells are deficient in peritoneal and pleural cavities but not in spleen. CXCL13 is produced by cells in the omentum and by peritoneal macrophages, and in adoptive transfers, B1 cells home to the omentum and the peritoneal cavity in a CXCL13-dependent manner. CXCL13(-/-) mice are deficient in preexisting phosphorylcholine (PC)-specific antibodies and in their ability to mount an anti-PC response to peritoneal streptococcal antigen. These findings provide insight into the mechanism of B1 cell homing and establish a critical role for B1 cell compartmentalization in the production of natural antibodies and for body cavity immunity.

Characterization of CCR9 expression and CCL25/thymus-expressed chemokine responsiveness during T cell development: CD3(high)CD69+ thymocytes and gammadeltaTCR+ thymocytes preferentially respond to CCL25

CCR9 mediates chemotaxis of thymocytes in response to CCL25/thymus-expressed chemokine, and its mRNA is selectively expressed in thymus and small intestine, the two known sites of T lymphopoiesis. To examine the expression of CCR9 during lymphocyte development, we generated polyclonal Ab that recognizes murine CCR9. CCR9 was expressed on the majority of immature CD4+CD8+ (double-positive) thymocytes, but not on immature CD4(-)CD8(-) (double-negative) thymocytes. CCR9 was down-regulated during the transition of double-positive thymocytes to the CD4+ or CD8+ (single-positive) stage, and only a minor subset of CD8+ lymph node T cells expressed CCR9. All CCR9+ thymocyte subsets migrated in response to CCL25; however, CD69+ thymocytes demonstrated enhanced CCL25-induced migration compared with CD69(-) thymocytes. Ab-mediated TCR stimulation also enhanced CCL25 responsiveness, indicating that CCL25-induced thymocyte migration is augmented by TCR signaling. Approximately one-half of all gammadeltaTCR+ thymocytes and peripheral gammadeltaTCR+ T cells expressed CCR9 on their surface, and these cells migrated in response to CCL25. These findings suggest that CCR9 may play an important role in the development and trafficking of both alphabetaTCR+ and gammadeltaTCR+ T cells.

CCR6 expression distinguishes mouse myeloid and lymphoid dendritic cell subsets: demonstration using a CCR6 EGFP knock-in mouse

The homing properties of subsets of lymphocytes and dendritic cells (DC) are regulated in part by the profile of chemokine receptors expressed. To determine how CCR6 influences cell trafficking, a mutant allele of the mouse CCR6 gene was produced that includes an enhanced green fluorescent protein (EGFP) reporter under the control of the CCR6 promoter. In mice heterozygous for the EGFP/CCR6 knock-in, CCR6 expression was detected on all mature B cells, subpopulations of splenic CD4(+) and CD8(+) T cells, and on some CD11c(+) DC. Most CD11b(+) myeloid DC expressed CCR6, but CD8alpha(+) lymphoid DC were negative for CCR6. Among myeloid DC, the CD4(+) subset was uniformly positive for CCR6 expression and the CD4(-) subset was mostly CCR6 positive. Epidermal Langerhans cells (LC) also expressed CCR6, but at lower levels than splenic myeloid DC. Culture of bone marrow precursors from the knock-in mice with GM-CSF for 4 to 6 days led to the appearance of a subset of CD11c(+) DC expressing CCR6. The differences in CCR6 expression among the major DC subsets indicate that CCR6 and its chemokine ligand MIP-3alpha participate in determining the positioning of DC subsets in epithelial and lymphoid tissues.