Identification of functional subsets by flow cytometry: intracellular detection of cytokine expression

Methods for analysis of T cell function have traditionally relied upon measurements of proliferation or cytokine expression in bulk cultures of PBMC in long term incubations with polyclonal mitogens or putative antigen. These techniques suffer from the drawback that they do not enable analysis of single cell responses in the context of unselected cellular backgrounds. In addition these methods are not sensitive enough to rapidly assess rare event responses characteristic of cognate memory T cell responses. This review discusses recently developed flow cytometric methods designed to rapidly assess leukocyte subset cytokine responses to polyclonal activators and specific antigen in PBMC and whole blood samples. These procedures determine the percentages of activated cells and the identification of leucocyte subsets capable of expressing various cytokines and cell surface antigens. The ability to assess key intracellular functional markers by multiparameter flow cytometry offers some unique advantages in a number of clinical applications. The technical simplicity and rapidity of the flow cytometric intracellular cytokine detection techniques described in this report, as well as the widespread availability of appropriate flow cytometers and cell surface directed antibodies in clinical laboratories, suggests the possibility that this technique could be broadly applicable to the clinical evaluation of immune status. Since any cell type can be identified with this approach, responses to a variety of clinically relevant stimuli in virtually any leukocyte subset can be evaluated including monocyte responses to LPS, and T cell responses to mitogens and a variety of bacterial and viral antigens. The significance of measuring low frequency antigen-specific responses with respect to clinical significance in assessing immune status in a variety of clinical conditions and determining efficacy or immunotoxicity of drugs and vaccine antigens is discussed.

Detection of antigen-specific T cell cytokine expression in whole blood by flow cytometry

We have recently described a highly sensitive flow cytometric technique, based on the ability to detect single cell expression of cytokines, to simultaneously quantitate and phenotypically characterize antigen-specific memory/effector T cells in PBMC cultures. In this report, we describe a simplified procedural modification which enables the rapid detection of low frequency memory CD4+ and CD8+ T cells expressing cytokines in response to soluble antigen in whole blood. When compared with T cell responses in PBMC cultures, whole blood cultures demonstrated similar but slightly higher percentages of T cells responsive to specific antigen. In addition, T cell responses to cytomegalovirus in whole blood were observed only in sensitized (seropositive) individuals, and CD4+ T cell responses could be blocked by anti-class II MHC antibodies. This procedure may provide a means to examine direct effects of pharmacological drug concentrations on T cell immunity in clinical samples.

Independent regulation of cutaneous lymphocyte-associated antigen expression and cytokine synthesis phenotype during human CD4+ memory T cell differentiation

Although considerable attention has been paid to the development of cytokine synthesis heterogeneity during memory T cell differentiation, little information is available on how this function is coregulated with homing receptor expression. The development of skin-homing, CD4+ memory T cells in the human provides an excellent model for such investigation, since 1) the skin supports both Th1- and Th2-predominant responses in different settings, and 2) the skin-homing capability of human memory T cells correlates with and appears to depend on expression of the skin-selective homing receptor cutaneous lymphocyte-associated Ag (CLA). In this study, we used multiparameter FACS analysis to examine expression of CLA vs IFN-gamma, IL-4, and IL-2 synthesis capabilities among fresh peripheral blood CD4+ memory T cells, and Th1 vs Th2 memory T cells generated in vitro from purified CD4+ naive precursors by cyclic activation in polarizing culture conditions. Among normal peripheral blood T cells, CLA expression was essentially identical among the IFN-gamma- vs IL-4-producing CD4+ memory subsets, clearly indicating the existence of in vivo mechanisms capable of producing both Th1 vs Th2 skin-homing T cells. In vitro differentiation of naive CD4+ T cells confirmed the independent regulation of CLA and all three cytokines examined, regulation that allowed differential production of IFN-gamma-, IL-4-, and IL-2-producing, CLA+ memory subsets. These studies also 1) demonstrated differences in regulatory factor activity depending on the differentiation status of the responding cell, and 2) revealed CLA expression to be much more rapidly reversible on established memory cells than cytokine synthesis capabilities.

Independent regulation of cutaneous lymphocyte-associated antigen expression and cytokine synthesis phenotype during human CD4+ memory T cell differentiation

Although considerable attention has been paid to the development of cytokine synthesis heterogeneity during memory T cell differentiation, little information is available on how this function is coregulated with homing receptor expression. The development of skin-homing, CD4+ memory T cells in the human provides an excellent model for such investigation, since 1) the skin supports both Th1- and Th2-predominant responses in different settings, and 2) the skin-homing capability of human memory T cells correlates with and appears to depend on expression of the skin-selective homing receptor cutaneous lymphocyte-associated Ag (CLA). In this study, we used multiparameter FACS analysis to examine expression of CLA vs IFN-gamma, IL-4, and IL-2 synthesis capabilities among fresh peripheral blood CD4+ memory T cells, and Th1 vs Th2 memory T cells generated in vitro from purified CD4+ naive precursors by cyclic activation in polarizing culture conditions. Among normal peripheral blood T cells, CLA expression was essentially identical among the IFN-gamma- vs IL-4-producing CD4+ memory subsets, clearly indicating the existence of in vivo mechanisms capable of producing both Th1 vs Th2 skin-homing T cells. In vitro differentiation of naive CD4+ T cells confirmed the independent regulation of CLA and all three cytokines examined, regulation that allowed differential production of IFN-gamma-, IL-4-, and IL-2-producing, CLA+ memory subsets. These studies also 1) demonstrated differences in regulatory factor activity depending on the differentiation status of the responding cell, and 2) revealed CLA expression to be much more rapidly reversible on established memory cells than cytokine synthesis capabilities.

Dendritic cell ontogeny: a human dendritic cell lineage of myeloid origin

Dendritic cells (DC) have been thought to represent a family of closely related cells with similar functions and developmental pathways. The best-characterized precursors are the epidermal Langerhans cells, which migrate to lymphoid organs and become activated DC in response to inflammatory stimuli. Here, we demonstrate that a large subset of DC in the T cell-dependent areas of human lymphoid organs are nonactivated cells and belong to a separate lineage that can be identified by high levels of the interleukin 3 receptor alpha chain (IL-3Ralphahi). The CD34+IL-3Ralphahi DC progenitors are of myeloid origin and are distinct from those that give rise to Langerhans cells in vitro. The IL-3Ralphahi DC furthermore appear to migrate to lymphoid organs independently of inflammatory stimuli or foreign antigens. Thus, DC are heterogeneous with regard to function and ontogeny.

Human recombinant interferon-beta influences T helper subset differentiation by regulating cytokine secretion pattern and expression of homing receptors

Type I interferons (IFN) are important regulators of both innate and acquired immunity. We have used an in vitro system of human CD4+ T cell differentiation to determine how IFN-beta influences development of T helper (Th) subsets and homing receptor expression. IFN-beta promoted differentiation of CD4+ T cells that produce low levels of both IFN-gamma and lymphotoxin compared to interleukin (IL)-12-derived Th1 CD4+ T cells. IFN-beta inhibited production of Th2 cytokines (IL-5 and IL-13) and augmented IL-12-mediated IL-10 secretion. In addition, IFN-beta significantly enhanced L-selection expression on CD4+ T cells and synergized with IL-12 to induce expression of cutaneous lymphocyte-associated antigen (CLA). This Th1 L-selectin+, CLA+ phenotype is characteristic of T cells found in normal human skin and suggests a role for type I IFN in the regulation of Th subset differentiation and tissue-specific homing receptors.

Determination of antigen-specific memory/effector CD4+ T cell frequencies by flow cytometry: evidence for a novel, antigen-specific homeostatic mechanism in HIV-associated immunodeficiency

The highly regulated secretion of effector cytokines by CD4+ T cells plays a critical role in immune protection against pathogens such as cytomegalovirus. Here, we directly compare the frequency and functional characteristics of cytomegalovirus-specific CD4+ memory/effector T cells in normal and HIV+ subjects using a novel, highly efficient multiparameter flow cytometric assay that detects the rapid intracellular accumulation of cytokine(s) after short-term (6 h) in vitro antigen stimulation. Responses in this assay correlate precisely with independent measures of sensitization history (e.g., seroreactivity), and allow the simultaneous assessment of multiple cytokines in single effector T cells. Healthy HIV- individuals manifested an average of 0.71, 0.72, 0.38, and 0.06% CD4+ T cells responding to cytomegalovirus with gamma-IFN, TNF-alpha, IL-2, and IL-4 production, respectively, with the simultaneous production of gamma-IFN, TNF-alpha, and IL-2 being the most common effector phenotype. Significantly, overall cytomegalovirus-specific CD4+ effector frequencies were markedly higher among 40% of HIV+ subjects (2.7-8.0%), and demonstrated a predominately polarized gamma-IFN+/TNF-alpha+/IL-2-/IL-4- phenotype. In contrast, CD4+ effector frequencies for heterologous, nonubiquitous viruses such as the mumps virus were low or absent in the HIV+ group. These data suggest the existence of homeostatic mechanisms in HIV disease that selectively preserve memory T cell populations reactive with ubiquitous pathogens such as cytomegalovirus-likely at the expense of T cell memory to more sporadically encountered infectious agents.

Immune reconstitution with donor-derived memory/effector T cells after orthotopic liver transplantation

Therapeutic hematopoietic stem cell transplantation has made great strides in recent years, providing curative therapy for many previously untreatable diseases. Nevertheless, the applicability and effectiveness of this procedure continues to be restricted by adverse immunoregulatory states, including graft rejection, graft vs. host disease (GvHD), and/or persistent immunodeficiency. Here, we provide evidence that long-term hematopoietic stem cell transplantation across major histocompatibility complex (MHC) barriers is possible in the human with limited adverse sequelae. We observed the rapid, complete, and stable replacement of recipient hematopoiesis and B lymphopoiesis with donor-derived cells approximately 6 weeks following orthotopic liver transplantation for hemochromatosis. Long-term T lineage reconstitution also occurred, but most intriguingly, derived almost exclusively from expansion of mature, memory/effector T cells from the transplanted liver. Although demonstrating both functional and molecular evidence of a simplified T cell receptor (TCR) repertoire and unable to become sensitized to "new" antigens (Ag), this patient demonstrated long-term clinical immunocompetence. Moreover, the transplanted T cells were effectively tolerant to host tissues as the patient did not manifest clinically significant GvHD off immunosuppressive therapy. These observations suggest that isolated memory/effector T cell populations have the potential of promoting stem cell engraftment in an allogeneic host without persistent GvHD, and to provide sufficient immune reconstitution to provide the recipient with long-term immune homeostasis.

Immunodetection of histone epitopes correlates with early stages of apoptosis in activated human peripheral T lymphocytes

By coupling intracellular staining with terminal deoxynucleotidyl transferase (TdT)-mediated labeling of internucleosomal DNA strand breaks in a flow cytometric assay, we observed a strong correlation between apoptosis-associated DNA strand breaks and immunoreactivity with the monoclonal antibody (MAb) B-F6 in activated human peripheral blood T lymphocytes (PBTs). Although MAb B-F6 has been reported to be specific for the cytokine interleukin-6, Western blot analysis of activated PBT lysates revealed that the predominant protein band detected by this MAb was 17 kd (p17), distinct from the 23-kd core protein and 26- to 30-kd mature glycosylated forms of interleukin-6. Immunoaffinity isolation and amino-terminal amino acid sequence analysis of p17 revealed identity with the histone H2B, a finding confirmed by Western blot analysis of purified histones and by similar staining of activated PBTs with an unrelated anti-histone MAb. Neither histone staining nor DNA strand breakage was observed in freshly isolated PBTs; however, after T cell activation, histone immunoreactivity appeared to precede the appearance of DNA strand breaks, with both increasing to a maximal level by day 3 after activation. Two-parameter confocal immunofluorescence microscopy of histone and DNA staining confirmed a lack of histone immunoreactivity in viable cells and demonstrated co-localization of histone epitopes with abnormally clumped chromatin in apoptotic cells. These data indicate that alteration of histone epitope accessibility is a marker of early apoptosis and suggest that multiparameter flow cytometric analysis of intracellular epitopes may be a powerful tool in the elucidation of intracellular mechanisms of apoptosis.

Neutrophil adhesion to 24-hour IL-1-stimulated endothelial cells under flow conditions

In this study, we examine neutrophil adhesion under flow conditions to cultured HUVEC stimulated for 4 or 24 h with IL-1. Interactions are measured using videomicroscopy and a parallel-plate flow system which is capable of distinguishing primary adhesion and rolling from secondary (firm) adhesion. We find that after 24 h, E-selectin does not contribute to primary adhesion, in contrast to a significant contribution after 4 h. Endothelial cell P-selectin does not contribute at either time point. Blocking or removing L-selectin from the neutrophil surface decreases adhesion 50 to 70% at either time point, and neuraminidase treatment of neutrophils decreases adhesion by 85%. These results suggest that after a 24-h stimulation, primary adhesion depends on a distinct selectin-like interaction in which a HUVEC receptor binds carbohydrates on neutrophil glycoproteins, including L-selectin. We also find that secondary adhesion in this system can be inhibited 90% with Ab blockade of CD18/ICAM-1 interactions after a 24-h stimulation, and that a combination of IL-1 and IL-4 selectively down-regulates the pathway for primary adhesion at 24 h. These results demonstrate that neutrophils adhere using different receptor pathways following 4- and 24-h stimulations, and provide experimental data characterizing some properties of the receptors involved. One of the pathways that is evident at 24 h appears to be a novel selectin-like interaction.

Neutrophil adhesion to 24-hour IL-1-stimulated endothelial cells under flow conditions

In this study, we examine neutrophil adhesion under flow conditions to cultured HUVEC stimulated for 4 or 24 h with IL-1. Interactions are measured using videomicroscopy and a parallel-plate flow system which is capable of distinguishing primary adhesion and rolling from secondary (firm) adhesion. We find that after 24 h, E-selectin does not contribute to primary adhesion, in contrast to a significant contribution after 4 h. Endothelial cell P-selectin does not contribute at either time point. Blocking or removing L-selectin from the neutrophil surface decreases adhesion 50 to 70% at either time point, and neuraminidase treatment of neutrophils decreases adhesion by 85%. These results suggest that after a 24-h stimulation, primary adhesion depends on a distinct selectin-like interaction in which a HUVEC receptor binds carbohydrates on neutrophil glycoproteins, including L-selectin. We also find that secondary adhesion in this system can be inhibited 90% with Ab blockade of CD18/ICAM-1 interactions after a 24-h stimulation, and that a combination of IL-1 and IL-4 selectively down-regulates the pathway for primary adhesion at 24 h. These results demonstrate that neutrophils adhere using different receptor pathways following 4- and 24-h stimulations, and provide experimental data characterizing some properties of the receptors involved. One of the pathways that is evident at 24 h appears to be a novel selectin-like interaction.

Lymphocyte homing and homeostasis

The integration and control of systemic immune responses depends on the regulated trafficking of lymphocytes. This lymphocyte "homing" process disperses the immunologic repertoire, directs lymphocyte subsets to the specialized microenvironments that control their differentiation and regulate their survival, and targets immune effector cells to sites of antigenic or microbial invasion. Recent advances reveal that the exquisite specificity of lymphocyte homing is determined by combinatorial "decision processes" involving multistep sequential engagement of adhesion and signaling receptors. These homing-related interactions are seamlessly integrated into the overall interaction of the lymphocyte with its environment and participate directly in the control of lymphocyte function, life-span, and population dynamics. In this article a review of the molecular basis of lymphocyte homing is presented, and mechanisms by which homing physiology regulated the homeostasis of immunologic resources are proposed.

CD44 and its ligand hyaluronate mediate rolling under physiologic flow: a novel lymphocyte-endothelial cell primary adhesion pathway

The extravasation of leukocytes from the blood into tissues occurs as a multistep process: an initial transient interaction ("rolling"), generally thought to be mediated by the selectin family of adhesion molecules, followed by firm adhesion, usually mediated by integrins. Using a parallel plate flow chamber designed to approximate physiologic flow in postcapillary venules, we have characterized a rolling interaction between lymphoid cells and adherent primary and cultured endothelial cells that is not selectin mediated. Studies using blocking monoclonal antibodies indicate that this novel interaction is mediated by CD44. Abrogation of the rolling interaction could be specifically achieved using both soluble hyaluronate (HA) and treatment of the adherent cells with HA-reactive substances, indicating that HA is the ligand supporting this rolling interaction. Some B and T cell lines, as well as normal lymphocytes, either constitutively exhibit rolling or can be induced to do so by phorbol ester or in vivo antigen activation. These studies indicate that CD44 and its principal ligand hyaluronate represent another receptor/carbohydrate ligand pair mediating a novel activation-dependent pathway of lymphocyte/endothelial cell adhesion.

Direct demonstration of cytokine synthesis heterogeneity among human memory/effector T cells by flow cytometry

The array of cytokines produced by T cells in effector sites is a primary means by which these cells mediate host defense. It is well recognized that cloned T cells are heterogeneous with regard to cytokine synthesis and, thus, in their ability to mediate specific immune responses, but the extent to which the patterns of cytokine secretion observed in cloned cells reflect actual populations of memory/effector T cells existing in vivo is largely unknown. Here, we report our findings using a multiparameter flow cytometric assay that allows simultaneous determination of an individual T-cell's ability to produce multiple cytokines and its phenotype after only short (4 to 8 hours) in vitro incubation with an activating stimulus and the secretion inhibitor Brefeldin A. This assay shows a rapid accumulation of interleukin-2 (IL-2), IL-4, and gamma-interferon (gamma-IFN) in the cytoplasm of CD4+ cells after stimulation with either accessory cell-independent (phorbol 12-myristate 13-acetate [PMA] + ionomycin [I]) or accessory cell-dependent (staphylococcal enterotoxins [SE] A and B) T-cell-activating stimuli. Further analysis showed that production of gamma-IFN and IL-4 is predominantly, if not exclusively, restricted to the CD45ROhigh memory/effector T-cell subset, whereas IL-2 may be produced by both the CD45ROhigh and CD45ROlow subsets. Simultaneous determination of IL-2 and gamma-IFN production among CD45ROhigh/CD4+ T cells showed distinct subsets that produce each of these cytokines alone (an average of 30% for IL-2 alone, 8% for gamma-IFN alone), both (16%), or neither (46%). Similar analyses with the small IL-4-producing memory/effector T-cell subset (only 4.3% of total CD4+/CD45ROhigh T cells) showed that an average of 51% of these IL-4-producing cells also synthesize average of 51% of these IL-4-producing cells also synthesize IL-2, 23% synthesize only IL-4, 16% synthesize all three cytokines, and 9.6% synthesize IL-4 and gamma-IFN. These patterns of cytokine synthesis were found to be similar with both PMA + I and SEA/SEB stimulation and were observed in both peripheral blood memory/effector CD4+ T cells and in T cells of similar phenotype obtained from cutaneous delayed-type hypersensitivity sites. Taken together, these data strongly support the in vivo existence of human memory/effector T-cell subsets with "preprogrammed" cytokine synthesis potential, although they suggest that these subsets may be more complex than originally proposed in the TH1/TH2 hypothesis.

Expression of CD45RB and CD27 identifies subsets of CD4+ memory T cells with different capacities to induce B cell differentiation

The capacity of four subsets of CD4+ memory T cells, defined by expression of CD45RB and CD27, to provide help for B cells was examined. Larger amounts of Ig were induced by CD45RBdimCD27- cells compared with the CD45RBdimCD27+ population, whereas CD45RBbrightCD27+ or CD27- cells were poor inducers of Ig synthesis. Mitomycin C treatment, which prevents suppressive activity, markedly enhanced Ig production supported by each subset except for CD45RBbrightCD27- cells. Mitomycin C-treated CD45RBdim cells remained the most efficient inducers of Ig production, but no difference was detected between CD27+ and CD27- cells. The subsets also differed in their ability to proliferate and secrete cytokines, but these differences did not explain variations in the capacity to provide help for B cells. Both CD27- subsets exhibited decreased proliferation and uniquely secreted IL-4, with the CD45RBdimCD27- subset producing the greatest quantities of IL-4. No differences in IL-2 and IFN-gamma production were found. IL-10 secretion increased with the acquisition of the CD45RBdim phenotype and, within the CD45RBdim cells, with the loss of CD27. Staining for cytoplasmic cytokines indicated that individual populations of CD27-CD4+ helper T cells produced either IL-4 or IFN-gamma, whereas more than half of the IL-4 producers also synthesized IL-2. Finally, the different abilities of CD4+ memory T cell subsets to support B cell differentiation did not relate to variations in the expression of CD40 ligand. These results indicate that within the CD4+ memory T cell population an increase of helper activity associates with the shift from a CD45RBbright to a CD45RBdim phenotype. Within the CD45RBdim subset, the loss of CD27 is associated with a reduction of suppressive activity.

Expression of CD45RB and CD27 identifies subsets of CD4+ memory T cells with different capacities to induce B cell differentiation

The capacity of four subsets of CD4+ memory T cells, defined by expression of CD45RB and CD27, to provide help for B cells was examined. Larger amounts of Ig were induced by CD45RBdimCD27- cells compared with the CD45RBdimCD27+ population, whereas CD45RBbrightCD27+ or CD27- cells were poor inducers of Ig synthesis. Mitomycin C treatment, which prevents suppressive activity, markedly enhanced Ig production supported by each subset except for CD45RBbrightCD27- cells. Mitomycin C-treated CD45RBdim cells remained the most efficient inducers of Ig production, but no difference was detected between CD27+ and CD27- cells. The subsets also differed in their ability to proliferate and secrete cytokines, but these differences did not explain variations in the capacity to provide help for B cells. Both CD27- subsets exhibited decreased proliferation and uniquely secreted IL-4, with the CD45RBdimCD27- subset producing the greatest quantities of IL-4. No differences in IL-2 and IFN-gamma production were found. IL-10 secretion increased with the acquisition of the CD45RBdim phenotype and, within the CD45RBdim cells, with the loss of CD27. Staining for cytoplasmic cytokines indicated that individual populations of CD27-CD4+ helper T cells produced either IL-4 or IFN-gamma, whereas more than half of the IL-4 producers also synthesized IL-2. Finally, the different abilities of CD4+ memory T cell subsets to support B cell differentiation did not relate to variations in the expression of CD40 ligand. These results indicate that within the CD4+ memory T cell population an increase of helper activity associates with the shift from a CD45RBbright to a CD45RBdim phenotype. Within the CD45RBdim subset, the loss of CD27 is associated with a reduction of suppressive activity.

Circulating allergen-reactive T cells from patients with atopic dermatitis and allergic contact dermatitis express the skin-selective homing receptor, the cutaneous lymphocyte-associated antigen

The cutaneous lymphocyte-associated antigen (CLA) is the major T cell ligand for the vascular adhesion molecule E-selectin, and it has been proposed to be involved in the selective targeting of memory T cells reactive with skin-associated Ag to cutaneous inflammatory sites. To further investigate the relation of CLA and cutaneous T cell responses, we analyzed the CLA phenotype of circulating memory T cells in patients with allergic contact dermatitis and atopic dermatitis (AD) alone vs in patients manifesting bronchopulmonary atopy (asthma with or without AD) and nonallergic individuals. Significant T cell proliferative responses to Ni, a contact allergen, and to the house dust mite (HDM), an allergen to which sensitization is often observed in AD and/or asthma, was noted only in allergic and atopic individuals, respectively. When the minor circulating CLA+CD3+CD45RO+ subset was separated from the major CLA-CD3+CD45RO+ subpopulation in Ni-sensitive subjects, the Ni-dependent memory T cell response was largely confined to the CLA+ subset. A similar restriction of the T cell proliferative response to the CLA+ memory subset was observed for HDM in patients with AD alone. In HDM-sensitive patients with asthma with or without AD, however, the CLA- subset exhibited a strong antigen-dependent proliferation, in contrast to patients with AD alone, whose CLA- subset proliferated very weakly to HDM. In asthma with or without AD, the HDM-dependent proliferation slightly predominated in the CLA- when compared to the CLA+ subset. The functional linkage between CLA expression and disease-associated T cell effector function in AD was also demonstrated by the finding that the circulating CLA+ T cell subset in AD patients, but not nonatopic controls, selectively showed both evidence of prior activation (human histocompatibility antigen-DR expression) and spontaneous production of interleukin 4 but not interferon-gamma. Taken together, these observations demonstrate the correlation of CLA expression on circulating memory T cells and disease-associated memory T cell responses in cutaneous hypersensitivity, and they suggest the existence of mechanisms capable of sorting particular T cell Ag specificities and lymphokine patterns into homing receptor-defined memory subsets.

Tumor dormancy and cell signaling. II. Antibody as an agonist in inducing dormancy of a B cell lymphoma in SCID mice

Tumor dormancy can be induced in a murine B cell lymphoma (BCL1) by immunizing BALB/c mice with the tumor immunoglobulin (Ig) before tumor cell challenge. In this report, we have investigated the immunological and cellular mechanisms underlying the induction of dormancy. BCL1 tumor cells were injected into SCID mice passively immunized with antibody against different epitopes on IgM or IgD with or without idiotype (Id)-immune T lymphocytes. Results indicate that antibody to IgM is sufficient to induce a state of dormancy. Antibodies against other cell surface molecules including IgD and CD44 (Pgp1) had no effect on tumor growth. Id-immune T cells by themselves also had no effect on tumor growth in SCID mice. However, simultaneous transfer of anti-Id and Id-immune T cells enhanced both the induction and duration of the dormant state. In vitro studies indicated that antibody to IgM induced apoptosis within several hours and cell cycle arrest by 24 h. Hyper cross-linking increased apoptosis. The Fc gamma RII receptor played little or no role in the negative signaling. Antibodies that did not negatively signal in vitro did not induce dormancy in vivo. The results suggest that anti-IgM plays a decisive role in inducing tumor dormancy to BCL1 by acting as an agonist of IgM-mediated signal transduction pathways.

Migration of skin-homing T cells across cytokine-activated human endothelial cell layers involves interaction of the cutaneous lymphocyte-associated antigen (CLA), the very late antigen-4 (VLA-4), and the lymphocyte function-associated antigen-1 (LFA-1)

The cutaneous lymphocyte-associated Ag (CLA) is expressed by a subset of circulating memory/effector T cells and by the vast majority of skin-infiltrating T cells. CLA is thought to target skin-associated T cells to inflammatory skin sites by interacting with endothelial cell ligand E-selectin (CD62E). We have examined adhesion molecules involved in the migration of human CLA+ and CLA- memory/effector T lymphocytes through IL-1- and TNF-alpha-activated and nonactivated HUVEC layers under static (nonflow) conditions. CLA-enriched memory/effector T lymphocytes migrated more actively across cytokine-activated HUVEC than CLA-depleted memory/effector T cells. This enhanced migration is dependent on the CLA/E-selectin interaction. mAb to very late Ag-4 (VLA-4) and vascular cell adhesion molecule-1 (VCAM-1) blocked the migration of CLA-enriched, but not of CLA-depleted, T cells across activated HUVEC. The observation that anti-VLA-4 and anti-CLA mAb did not show additional inhibition supports the concept that CLA and VLA-4 are sequentially involved in the extravasation. The fact that only CLA+ T cells were inhibited by the anti-VLA-4 mAb suggests that, in this system, CLA engagement is required for using the VLA-4/VCAM-1 pathway. Our studies demonstrate that CLA+ T cells use LFA-1/intercellular leukocyte adhesion molecule-1 (ICAM-1) for transmigration but that CLA expression is not required for the LFA-1/ICAM-1-dependent transmigration because anti-CD18/CD11a mAbs and anti-ICAM-1 mAbs were able to block T cell migration regardless of the activation state of HUVEC or the CLA expression by T cells. Taken together, our results suggest that CLA has a homing function in conducting the T cell to interact with LFA-1/ICAM-1 and/or VLA-4/VCAM-1; this results in enhanced adhesion and migration across cytokine-activated endothelial cells.

Migration of skin-homing T cells across cytokine-activated human endothelial cell layers involves interaction of the cutaneous lymphocyte-associated antigen (CLA), the very late antigen-4 (VLA-4), and the lymphocyte function-associated antigen-1 (LFA-1)

The cutaneous lymphocyte-associated Ag (CLA) is expressed by a subset of circulating memory/effector T cells and by the vast majority of skin-infiltrating T cells. CLA is thought to target skin-associated T cells to inflammatory skin sites by interacting with endothelial cell ligand E-selectin (CD62E). We have examined adhesion molecules involved in the migration of human CLA+ and CLA- memory/effector T lymphocytes through IL-1- and TNF-alpha-activated and nonactivated HUVEC layers under static (nonflow) conditions. CLA-enriched memory/effector T lymphocytes migrated more actively across cytokine-activated HUVEC than CLA-depleted memory/effector T cells. This enhanced migration is dependent on the CLA/E-selectin interaction. mAb to very late Ag-4 (VLA-4) and vascular cell adhesion molecule-1 (VCAM-1) blocked the migration of CLA-enriched, but not of CLA-depleted, T cells across activated HUVEC. The observation that anti-VLA-4 and anti-CLA mAb did not show additional inhibition supports the concept that CLA and VLA-4 are sequentially involved in the extravasation. The fact that only CLA+ T cells were inhibited by the anti-VLA-4 mAb suggests that, in this system, CLA engagement is required for using the VLA-4/VCAM-1 pathway. Our studies demonstrate that CLA+ T cells use LFA-1/intercellular leukocyte adhesion molecule-1 (ICAM-1) for transmigration but that CLA expression is not required for the LFA-1/ICAM-1-dependent transmigration because anti-CD18/CD11a mAbs and anti-ICAM-1 mAbs were able to block T cell migration regardless of the activation state of HUVEC or the CLA expression by T cells. Taken together, our results suggest that CLA has a homing function in conducting the T cell to interact with LFA-1/ICAM-1 and/or VLA-4/VCAM-1; this results in enhanced adhesion and migration across cytokine-activated endothelial cells.

Milk-induced eczema is associated with the expansion of T cells expressing cutaneous lymphocyte antigen

The extravasation of T cells at sites of inflammation is critically dependent on the activity of homing receptors (HR) involved in endothelial cell recognition and binding. Two such HR (the cutaneous lymphocyte antigen [CLA] and L-selectin) have been shown to be selectively involved in T cell migration to skin and peripheral lymph nodes, respectively. This study was designed to assess the relationship between the organ specificity of an allergic reaction to food and the expression of HR on T cells activated in vitro by the relevant food allergen. Peripheral blood mononuclear cells were isolated from seven milk allergic children with a history of eczema when exposed to milk. All patients had a positive prick skin test and double-blind placebo-controlled food challenge to milk. 10 children with either allergic eosinophilic gastroenteritis or milk-induced enterocolitis and 8 nonatopic adults served as controls. Five-parameter flow cytometry using monoclonal antibodies was used for detection of the specific HR on freshly isolated T cells versus T cell blasts induced by a 6-d incubation with casein, as compared with Candida albicans. After in vitro stimulation with casein, but not C. albicans, patients with milk allergy and atopic dermatitis had a significantly greater percentage of CLA+ T cells (P < 0.01) than controls with milk-induced enterocolitis, allergic eosinophilic gastroenteritis, or nonatopic healthy controls. In contrast, the percentage of L-selectin-expressing T cells did not differ significantly between these groups. These data suggest that after casein stimulation allergic patients with milk-induced skin disease have an expanded population of CLA+ T cells, as compared with nonatopics or allergic patients without skin involvement. We postulate that heterogeneity in the regulation of HR expression on antigen-specific T cells may play a role in determining sites of involvement in tissue-directed allergic responses.

Bacterial superantigens induce T cell expression of the skin-selective homing receptor, the cutaneous lymphocyte-associated antigen, via stimulation of interleukin 12 production

T lymphocyte infiltration is a prominent feature of the skin inflammation associated with infections by toxin (superantigen)-secreting Staphylococcus aureus or Streptococcus bacteria. The cutaneous lymphocyte-associated antigen (CLA) has been hypothesized to be a homing receptor (HR) involved in selective migration of memory/effector T cells to the skin. Since the expression of this putative skin-selective HR is known to be under strict microenvironmental control, we sought to determine the effect of staphylococcal and streptococcal toxins on T cell expression of CLA. After in vitro stimulation of peripheral blood mononuclear cells with staphylococcal enterotoxin B, toxic shock syndrome toxin-1, and streptococcal pyrogenic exotoxins A and C, there was a significant increase in the numbers of CLA+ T cell blasts (p < 0.01), but not blasts bearing the mucosa-associated adhesion molecule alpha e beta 7-integrin, compared with T cells stimulated with phytohemaglutinin (PHA) or anti-CD3. Bacterial toxins were also found to specifically induce interleukin (IL) 12 production. More importantly, induction of toxin-induced CLA expression was blocked by anti-IL-12, and the addition of IL-12 to PHA-stimulated T cells induced CLA, but not alpha e beta 7-integrin, expression. These data suggest that bacterial toxins induce the expansion of skin-homing CLA+ T cells in an IL-12-dependent manner, and thus may contribute to the development of skin rashes in superantigen-mediated diseases.

A two-step adhesion cascade for T cell/endothelial cell interactions under flow conditions

Neutrophil adherence to endothelial cells (ECs) under conditions of flow occurs in successive steps, including selectin-dependent primary adhesion and CD18-dependent secondary adhesion. We used a parallel-plate flow chamber to assess the steps in T cell adherence in vitro. On monolayers of L cells transfected with the EC adhesion molecules E-selectin, vascular cell adhesion molecule-1 (VCAM-1), or intercellular adhesion molecule-1 (ICAM-1), E-selectin was capable of mediating only primary adhesion, ICAM-1 was capable of mediating only secondary adhesion, and VCAM-1 was capable of mediating both primary and secondary adhesion. Studies using human umbilical vein EC monolayers stimulated for 24 h with IL-1 also revealed distinct primary and secondary steps in T cell adhesion under flow, and the secondary adhesion was inhibited > 90% by blocking both VCAM-1/alpha 4 beta 1 integrin and ICAM-1/CD18 integrin pathways. However, the primary adhesion under conditions of flow could not be attributed to any of the mechanisms known to support adhesion of leukocytes to ECs. Alone, this pathway was shown to mediate T cell rolling and was a necessary prerequisite for engagement of the two integrin pathways in this system. Thus, T cell adherence to 24-h IL-1-stimulated human umbilical vein ECs at venular wall shear stresses involves at least two successive steps, with clear molecular distinctions from the mechanisms accounting for neutrophil/EC adhesion.

Control of lymphocyte homing

The expression of immunity, both protective and pathologic, is critically dependent on the appropriate distribution of 'lymphoid resources' among the tissues of the body. The 'homing' mechanisms mediating this distribution have proven to have an astounding plasticity--directing, under strict microenvironmental control, the selective recruitment of specific lymphocyte subsets to the various secondary lymphoid tissues and extralymphoid immune effector sites. The past year has seen significant progress in our understanding in three areas: the molecular basis of lymphocyte interactions with endothelium, providing new insight into the complex multistep process of lymphocyte extravasation; the role of extravascular matrix and cells in retaining lymphocytes within tissues; and the mechanisms by which local microenvironments differentially regulate adhesion molecule expression and function so as to provide for site-selective lymphocyte homing.