Subspecialization of CXCR5+ T cells: B helper activity is focused in a germinal center-localized subset of CXCR5+ T cells.

The T helper (Th) cell pool is composed of specialized cells with heterogeneous effector functions. Apart from Th1 and 2 cells, CXCR5+ T cells have been suggested to be another type of effector T cell specialized for B cell help. We show here that CXCR5+ T cells are heterogeneous, and we identify subsets of CXCR5+ CD4 T cells that differ in function and microenvironmental localization in secondary lymphoid tissues. CD57+CXCR5 T cells, hereafter termed germinal center Th (GC-Th) cells, are localized only in GCs, lack CCR7, and are highly responsive to the follicular chemokine B lymphocyte chemoattractant but not to the T cell zone EBI1-ligand chemokine. Importantly, GC-Th cells are much more efficient than CD57-CXCR5+ T cells or CXCR5- T cells in inducing antibody production from B cells. Consistent with their function, GC-Th cells produce elevated levels of interleukin 10 upon stimulation which, with other cytokines and costimulatory molecules, may help confer their B cell helper activity. Our results demonstrate that CXCR5+ T cells are functionally heterogeneous and that the GC-Th cells, a small subset of CXCR5+ T cells, are the key helpers for B cell differentiation and antibody production in lymphoid tissues.

Expression of alpha4beta7 and E-selectin ligand by circulating memory B cells: implications for targeted trafficking to mucosal and systemic sites.

We have examined the expression of homing receptors on circulating memory B cells subsets. Blood IgD+ (naive) B cells homogeneously express a high level of intestinal homing receptor, alpha4beta7, but IgD- (putative memory) B cells comprise distinct alpha4beta7+ and alpha4beta7- subsets. Naive and alpha4beta7+ memory B cells but not alpha4beta7- cells bind MAdCAM-1, suggesting that alpha4beta7 expression may predict B cell intestinal homing. In contrast, alpha4beta7+ and alpha4beta7- B cells bind well to VCAM-1, possibly allowing recruitment of both subsets to extra-intestinal sites, including those tissues of the "common mucosal immune system" characterized by vascular VCAM-1 expression. sIgA+ B cells, which are associated with mucosal immunity in the gut and elsewhere, are heterogeneous in homing receptor expression--with discrete subsets expressing alpha4beta7, L-selectin, and cutaneous lymphocyte antigen (CLA). sIgA+ CLA+ B cells are enriched by binding to E-selectin, suggesting that CLA may participate in B cell homing to nonintestinal mucosal tissues characterized by vascular E-selectin expression, such as chronically inflamed bronchial or oral mucosal. We conclude that circulating human peripheral blood memory B cells, like T cells, consist of discrete homing receptor-defined subsets. This diversity in homing phenotypes is apparent even among sIgA (presumptive mucosal) memory B cells, implying heterogeneity in trafficking mechanisms to different target mucosal surfaces.

The memory B cell subset responsible for the secretory IgA response and protective humoral immunity to rotavirus expresses the intestinal homing receptor, alpha4beta7.

Infection of mice with murine rotaviruses induces life-long immunity, characterized by high levels of IgA in the intestine and large numbers of rotavirus (RV)-specific Ab-secreting cells in gut-associated lymphoid tissues. Lymphocyte trafficking into gut-associated lymphoid tissues is mediated by interaction of the alpha4beta7 integrin on lymphocytes with the vascular mucosal addressin cell adhesion molecule-1. To determine whether B cell memory for RV correlates with alpha4beta7 expression, we transferred sorted B220+ phenotypically defined memory (IgD- alpha4beta7(high) and IgD- alpha4beta7-) and naive (IgD+ alpha4beta7+) splenocytes into recombination-activating gene-2 knockout mice (B and T cell-deficient) that were chronically infected with RV. Only mice receiving alpha4beta7(high) memory (IgD-) B cells produced RV-specific IgA in the stool, cleared the virus, and were immune to reinfection. Alpha4beta7(high) (but not alpha4beta7-) memory B cells from donors boosted as much as 7 mo previously also cleared the virus, indicating that alpha4beta7(high) memory B cells maintain long term functional immunity to RV. Although only alpha4beta7(high) memory cells provided mucosal immunity, alpha4beta7- cells from recently boosted donor animals could generate RV-specific serum IgG, but, like naive (IgD+) B cells, were unable to induce viral clearance even 60 days after cell transfer. These data indicate that protective immunity for an intestinal pathogen, RV, resides in memory phenotype B cells expressing the intestinal homing receptor, alpha4beta7.

Adhesion molecule phenotype of T lymphocytes in inflamed CNS.

The phenotype of T cells in the central nervous system (CNS) in two models of chronic inflammation (experimental allergic encephalomyelitis and Corynebacterium parvum-induced inflammation) was compared to that of T cells in gut and chronically inflamed subcutaneous tissue and lung. CNS T cells display a similar phenotype in both inflammatory models, and are phenotypically unique compared to T cells from the other inflamed tissues. T cells from inflamed CNS are mainly CD4+ and are the only population examined that express a typical activated/memory phenotype: CD44high/LFA-1high/ICAM-1high/CD45RBlow. The CNS T cells are alpha4beta7-integrin(negative), but express alpha4-integrin and activated beta1 integrin, suggesting expression of the alpha4beta1-heterodimer in an activated state. In contrast, most T cells in gut express low levels of activated beta1 integrin. The CNS T cells lack expression of alpha6 and alphaE integrin chains and L-selectin. In inflamed CNS and inflamed subcutaneous tissue, approximately 50% of T cells express high affinity ligands for P-selectin while fewer than 10% express high affinity ligands for E-selectin. In summary, our data show that, independent of the inflammatory stimulus, T cells recruited into the inflamed CNS are phenotypically distinct from T cells in other inflamed tissues. This finding leads us to hypothesize the existence of a phenotypically distinct 'CNS-seeking' T lymphocyte population.

Expression of the mucosal homing receptor alpha4beta7 correlates with the ability of CD8+ memory T cells to clear rotavirus infection.

The integrin alpha4beta7 plays an important role in lymphocyte homing to mucosal lymphoid tissues and has been shown to define a subpopulation of memory T cells capable of homing to intestinal sites. Here we have used a well-characterized intestinal virus, murine rotavirus, to investigate whether memory/effector function for an intestinal pathogen is associated with alpha4beta7 expression. Alpha4beta7(hi) memory phenotype (CD44hi), alpha4beta7- memory phenotype, and presumptively naive (CD44(lo)) CD8+ T lymphocytes from rotavirus-infected mice were sorted and transferred into Rag-2 (T- and B-cell-deficient) recipients that were chronically infected with murine rotavirus. Alpha4beta7(hi) memory phenotype CD8+ cells were highly efficient at clearing rotavirus infection, alpha4beta7- memory cells were inefficient or ineffective, depending on the cell numbers transferred, and CD44(lo) cells were completely unable to clear chronic rotavirus infection. These data demonstrate that functional memory for rotavirus resides primarily in memory phenotype cells that display the mucosal homing receptor alpha4beta7.

Expression of mucosal homing receptor alpha4beta7 by circulating CD4+ cells with memory for intestinal rotavirus.

The integrin alpha4beta7 mediates lymphocyte binding to mucosal addressin cell adhesion molecule-1, and its expression defines lymphocytes capable of trafficking through the intestines and the intestinal lymphoid tissues. We examined the ability of discrete alpha4beta7(hi) and alpha4beta7- subsets of circulating memory phenotype (CD45RA-) CD4+ T cells to proliferate in response to rotavirus, a ubiquitous intestinal pathogen. alpha4beta7(hi) memory (CD45RA-) CD4+ T cells displayed much greater reactivity to rotavirus than alpha4beta7- memory or naive (CD45RA+) CD4+ T cells. In contrast, alpha4beta7- memory cells were the predominant population responsive to mumps antigen after intramuscular vaccination. Our results are consistent with the conclusion that natural rotavirus infection, an enteric pathogen, results in a specific circulating memory CD4+ response that is largely limited to the gut-homing alpha4beta7+ subpopulation. This phenotype is not shared with memory cells elicited by intramuscular immunization (shown here) or by skin contact allergens. The results support the hypothesis that gut trafficking memory CD4+ T cells comprise cellular memory for intestinal antigens and suggest that regulated expression of alpha4beta7 helps target and segregate intestinal versus systemic immune response.

Evidence for CD8+ T-cell immunity to murine rotavirus in the absence of perforin, fas, and gamma interferon.

We recently showed that class I-restricted CD8+ T cells mediate clearance of primary rotavirus infection in mice: JHD knockout (JHD -/-) (B-cell-deficient) mice depleted of CD8+ T cells become chronically infected with murine rotavirus, and beta2 microglobulin knockout (beta2m -/-) mice have delayed but complete clearance of primary rotavirus infection. In the present work we have analyzed the mechanism used by CD8+ T cells to clear rotavirus infection. We first determined that perforin knockout (perforin -/-) mice and lpr (fas-deficient) mice clear rotavirus infection with the same kinetics as control mice. When perforin -/- or perforin +/+ mice were depleted of CD8+ T cells by administration of an anti-CD8 monoclonal antibody, they showed a delay of 1 to 2 days in the clearance of rotavirus infection compared to the clearance time for untreated control mice, indicating that CD8+ T cells in both groups of mice participate in the resolution of primary rotavirus infection. In addition, passively transferred CD8+ T cells from rotavirus-infected perforin +/+ and perforin -/- mice were able to mediate viral clearance in Rag 2 knockout (Rag 2 -/-) mice chronically infected with rotavirus with similar kinetics, suggesting that CD8+ T cells from perforin -/- mice are as efficient as CD8+ T cells from perforin +/+ mice in clearing a rotavirus infection. Gamma interferon (IFN-gamma) was also shown to be unnecessary for the antirotavirus effect of CD8+ T cells: IFN-gamma knockout (IFN-gamma -/-) mice and JHD -/-, perforin -/-, and perforin +/+ mice depleted of IFN-gamma by administration of an anti-IFN-gamma monoclonal antibody cleared rotavirus infection with the same kinetics as those for control mice. Hence, CD8+ T cells have an antirotaviral effect that is not mediated by perforin and appears to be independent of fas and the release of IFN-gamma.

Altered oncoprotein expression and apoptosis in myelodysplastic syndrome marrow cells.

Ineffective hematopoiesis with associated cytopenias and potential evolution to acute myeloid leukemia (AML) characterize patients with myelodysplastic syndrome (MDS). We evaluated levels of apoptosis and of apoptosis-related oncoproteins (c-Myc, which enhances, and Bcl-2, which diminishes apoptosis) expressed within CD34+ and CD34- marrow cell populations of MDS patients (n = 24) to determine their potential roles in the abnormal hematopoiesis of this disorder. Marrow cells were permeabilized and CD34+ and CD34- cells were separately analyzed by FACS to detect: (1) a subdiploid (sub-G1) DNA population, and (2) expression of Bcl-2 and c-Myc oncoproteins. Within the CD34+ subset, a significantly increased percentage of cells demonstrated apoptotic/sub-G1 DNA content in early (ie. refractory anemia) MDS patients compared with normal individuals and AML patients (mean values: 9.1% > 2.1% > 1.2%). Correlated with these findings, the ratio of expression of c-Myc to Bcl-2 oncoproteins among CD34+ cells was significantly increased for MDS patients compared to those from normal and AML individuals (mean values: 1.6 > 1.2 > 0.9). Bcl-2 and c-Myc oncoprotein levels were maturation stage-dependent, with high levels expressed within CD34+ marrow cells, decreasing markedly with myeloid maturation. Treatment of seven MDS patients with the cytokines granulocyte colony-stimulating factor plus erythropoietin was associated with decreased levels of apoptosis within CD34+ marrow cells and may contribute to the enhanced hematopoiesis in vivo that was shown. These findings are consistent with the hypothesis that altered balance between cell-death (eg, c-Myc) and cell-survival (eg, Bcl-2) programs were associated with the increased degrees of apoptosis present in MDS hematopoietic precursors and may contribute to the ineffective hematopoiesis in this disorder, in contrast to decreased apoptosis and enhanced leukemic cell survival in AML.

A fundamental subdivision of circulating lymphocytes defined by adhesion to mucosal addressin cell adhesion molecule-1. Comparison with vascular cell adhesion molecule-1 and correlation with beta 7 integrins and memory differentiation.

The leukocyte integrin alpha 4 beta 7 is a receptor for the vascular mucosal addressin cell adhesion molecule-1 (MAdCAM-1). Most circulating B and T lymphocytes in man are alpha 4+, and on these cells the regulated display of the beta 7 integrin chain determines the expression of alpha 4 beta 7 and, in large part, binding to MAdCAM-1. Among CD4+ T cells, beta 7 high memory cells (including the L-selectin+ subset) bind MAdCAM-1 better than beta 7int naive cells; whereas beta 7- memory cells,including skin homing lymphocytes, interact poorly if at all. Circulating alpha E beta 7+ T cells are alpha 4 beta 7high and also bind MAdCAM-1 well. B cells are also subdivided by beta 7 expression, and beta 7+ B cells bind MAdCAM-1 better than the beta 7low/- subset. The related vascular ligand vascular cell adhesion molecule-1 (VCAM-1), expressed on endothelium primarily in nonmucosal sites of inflammation, interacts with blood lymphocytes (including beta 7high T cells) almost exclusively via alpha 4 beta 1 and binds beta 7low/-(beta 1high) better than beta 7+ B cells and memory cells better than naive CD4+ cells. beta 7-(beta 1high) memory T cells are somewhat enriched over beta 7high memory cells at low (but not at high) VCAM-1 densities. Interestingly, CD56+ NK cells, which express both alpha 4 beta 7 and alpha 4 beta 1, bind well to VCAM-1 but poorly to MAdCAM-1. The findings indicate that the display and function of alpha 4 beta 7 determine integrin-dependent blood lymphocyte interactions with MAdCAM-1, thus delineating discrete mucosal vs nonmucosal lymphocyte populations in vivo; that alpha 4 beta 1 dominates blood lymphocyte interactions with VCAM-1; and that quantitative and qualitative regulation of MAdCAM-1 vs VCAM-1 can critically control the recruitment of specialized lymphocyte subsets during inflammation.

Distribution of alpha 4 beta 7 and alpha E beta 7 integrins on thymocytes, intestinal epithelial lymphocytes and peripheral lymphocytes.

Beta 7 is expressed on subsets of thymocytes, while T and B lymphocytes show heterogeneous expression of beta 7. Here, we examine the phenotype of the thymocyte and lymphocyte subsets which express alpha 4 beta 7 and alpha E beta 7 using mAb against alpha E, beta 7 and mAb DATK32 which recognizes a combinatiorial epitope on alpha 4 beta 7+ thymocytes have a mature phenotype: TcR+, CD11a(hi)CD44(hi)HSA(dull). Small subsets of double-negative CD4-CD8-, single-positive CD4+ and CD8+ thymocytes express beta 7, while double-positive CD4+CD8+ thymocytes are beta 7-. However, two integrins alpha E beta 7 and alpha 4 beta 7 recognized by anti-beta 7 are not expressed on an identical subpopulation of thymocytes, as alpha E beta 7+ alpha 4 beta 7-, alpha E beta 7 + alpha 4 beta 7+ and alpha E beta 7- alpha 4 beta 7+ thymocyte subsets are evident. Similarly, intraepithelial lymphocytes express high levels of alpha E beta 7 but little alpha 4 beta 7. In the spleen, Peyer's patches and lymph nodes, alpha 4 beta 7 is expressed at higher levels on most B lymphocytes than on the majority of T lymphocytes, while a small subset of T lymphocytes, which includes both CD4+ and CD8+ lymphocytes, express high levels of beta 7 in the form of alpha 4 beta 7 and alpha E beta 7, although, as observed with lymphocytes, not all alpha 4 beta 7 hi CD4+ lymphocytes expressed alpha 4 beta 7. The population of alpha 4 beta 7 hi CD4 lymphocytes are enriched in Peyer's patches and form subsets of the memory CD4+ lymphocyte population, which can be further subdivided on the basis of alpha E beta 7, L-selectin and alpha 4 expression. Therefore, memory CD4+ lymphocytes are highly heterogeneous in their expression of adhesion receptors, and presumably these subpopulations will exhibit very different trafficking properties.

A significant soluble keratin fraction in 'simple' epithelial cells. Lack of an apparent phosphorylation and glycosylation role in keratin solubility.

We studied the solubility of keratin polypeptides 8 and 18 (K8/18), which are the predominant intermediate filaments in the human colonic epithelial cell line HT29. We find that asynchronously growing cells (G0/G1 stage of the cell cycle) have a substantial pool of soluble keratin that constitutes approx. 5% of total cellular keratin. This soluble keratin pool was observed after immunoprecipitation of K8/18 from the cytosolic fraction of cells disrupted using three detergent-free methods. Several other cell lines showed a similar significant soluble cytosolic K8/18 pool. Arrest of HT29 cells in G2/M stage of the cell cycle was associated with a concurrent increase in keratin solubility. Comparison of K8/18 obtained from the soluble cytosolic fraction and the insoluble high-speed pellet fraction showed similar levels of phosphorylation and glycosylation and similar tryptic radiolabeled phospho- and glycopeptide patterns. Soluble K8/18 can form characteristic 10 nm filaments in vitro as determined by electron microscopy. Cross-linking of soluble K8/18 followed by immunoprecipitation resulted in dimeric and tetrameric forms, based on migration in SDS-polyacrylamide gels. In addition, cross-linked and native soluble K8/18 showed similar migration on nondenaturing gels and similar sedimentation after sucrose density gradient centrifugation. Our results indicate that simple epithelial keratins are appreciably more soluble than previously recognized. The soluble keratin form is assembly competent and appears to be primarily tetrameric. Although K8/18 solubility was found to increase during mitotic arrest, glycosylation and phosphorylation did not play an obvious role in generating the soluble fraction, suggesting an alternate mechanism for keratin solubility.

The cutaneous lymphocyte antigen is a skin lymphocyte homing receptor for the vascular lectin endothelial cell-leukocyte adhesion molecule 1.

A skin-associated population of memory T lymphocytes, defined by expression of the cutaneous lymphocyte antigen (CLA), binds selectively and avidly to the vascular lectin endothelial cell-leukocyte adhesion molecule 1 (ELAM-1), an interaction that may be involved in targeting of CLA+ T cells to cutaneous sites of chronic inflammation. Here we present evidence that CLA itself is the (or a) lymphocyte homing receptor for ELAM-1. Antigen isolated with anti-CLA monoclonal antibody HECA-452 from human tonsillar lysates avidly binds ELAM-1 transfected mouse cells. Anti-CLA antibody blocks T lymphocyte binding to ELAM-1 transfectants. HECA-452 and ELAM-1 binding to lymphocytes or to isolated tonsillar HECA-452 antigen is abrogated by neuraminidase treatment implying a prominent role for sialic acid in CLA structure and function. The dominant form of CLA on T cells is immunologically distinct from the major neutrophil ELAM-1 ligand, the sialyl Lewis x (sLex) antigen (NeuAc alpha 2-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc), which is absent, weakly expressed, or masked on T cells. However, neuraminidase treatment of CLA+ T cells, but not of CLA- T cells, reveals Lewis x (CD15) structures. In combination with the known requirement for terminal NeuAc alpha 2-3Gal and fucose residues attached to N-acetylglucosamine for ELAM-1 and HECA-452 binding, this finding suggests that CLA may comprise an additionally sialylated or otherwise modified form of sLex. The identification of a lymphocyte homing receptor for skin may permit novel approaches to the diagnosis and therapy of cutaneous and inflammatory disorders.

Differential expression of homing-associated adhesion molecules by T cell subsets in man.

The ability of lymphocyte populations to recognize and bind high endothelial venules during homing into lymphoid tissues and sites of chronic inflammation is critically dependent on their expression of certain homing-associated adhesion molecules known as homing receptors (HR). In animal models, certain lymphocyte populations, particularly subsets of memory or previously activated lymphocytes, demonstrate tissue-selective homing behavior, and it has been hypothesized that differential expression of HR accounts for this selective migration. In this study, we analyzed expression of human HR--the Dreg 56/Leu 8-defined peripheral lymph node (PLN) HR (also known as LECAM-1), H-CAM (CD44), and alpha 4-integrins (CD49d; VLA-4)--among subsets of thymocytes and peripheral blood T cells to identify populations with differential homing potential. In the thymus, these three HR classes are differentially regulated relative to phenotypically defined maturational stages, but are all expressed on the mature, surface CD3high subset. In the peripheral blood, virgin T cells (LFA-3/CD58low) show uniform high expression of the PLN HR, uniform relatively low expression of H-CAM and alpha 4-integrin, and lack markers of tissue association--the mucosal and cutaneous lymphocyte associated Ag (MLA and CLA Ags) defined by mAb Ber ACT8 and HECA-452, respectively. In contrast, circulating memory T cells (LFA-3/CD58high) are bimodal with respect to PLN HR expression, show uniform high expression of H-CAM and alpha 4-integrin, and contain essentially all the CLA and MLA Ag-bearing T cells. The circulating skin-associated T cell subset (CLA Ag+; 10 to 15% of total T cells) is predominantly PLN HR+, and shows high levels of both the alpha 4- and beta 1-integrin chains. The distinct mucosa-associated T cell subset (MLA Ag+; 1 to 3% of peripheral blood T cells) is predominantly PLN HR-; and is alpha 4high, but beta 1low. These findings indicate the independent regulation of homing-associated adhesion molecules among populations of memory/previously activated T cells, and suggest that the expression patterns of these molecules contribute to, or perhaps determine, the tissue distribution of these subsets.

A unique phenotype of skin-associated lymphocytes in humans. Preferential expression of the HECA-452 epitope by benign and malignant T cells at cutaneous sites.

It has been proposed that the skin is a functionally unique compartment of the immune system, although little direct evidence supporting this hypothesis has been presented. Here we show that lymphocyte populations at cutaneous sites can be differentiated from otherwise similar populations at noncutaneous sites by their preferential expression of an epitope defined by the MAb HECA-452. This MAb recognizes a predominantly 200-kd cell-surface glycoprotein present on about 16% of peripheral blood T cells, including both CD4+ and CD8+ T cells (17% and 11% HECA-452+, respectively), as well as TCR-delta-bearing T cells (32%+). Most thymocytes (99%) lacked HECA-452 antigen expression, and essentially all the HECA-452+ peripheral blood T cells were found in the adhesion molecule high, CD45R low putative memory cell subset, findings suggesting that HECA-452 expression develops peripherally as a consequence of antigenic stimulation. However, the HECA-452 antigen is not a conventional activation antigen because it was not upregulated with mitogen stimulation of peripheral blood T cells. Most significantly, among 54 diverse specimens of normal/reactive lymphoid tissues and sites of chronic inflammation, there was a clear association of lymphocyte HECA-452 expression and cutaneous location. In extracutaneous sites (n = 38) only about 5% of lymphocytes within the T-cell areas of these tissues expressed this antigen, whereas in inflammatory skin lesions (n = 16), 85% were HECA-452+. The association of HECA-452 expression and cutaneous location was also seen in a series of T-cell lymphomas. The malignant cells of 16 of 18 cases of epidermotropic (patch/plaque) stage mycosis fungoides were HECA-452+, as well as 2 of 7 nonmycosis fungoides peripheral T-cell lymphomas in skin. In contrast, this antigen was not expressed in thymic (lymphoblastic) lymphomas (n = 14), nonepidermotropic (tumor) stage mycosis fungoides (n = 5), and noncutaneous peripheral T-cell lymphomas (n = 15). Among lymphocytes, the preferential expression of the HECA-452 determinant by cutaneous T cells supports the hypothesis that the skin constitutes a immunologically unique lymphoid tissue and suggests that this molecule may play a role in either lymphocyte homing to skin or in lymphocyte interactions with the epidermis.