Epidermal T lymphocytes and dendritic cells in chronic plaque psoriasis: the effects of PUVA treatment.

The numbers and HLA-DR expression of T cell subsets and dendritic cells in chronic psoriatic plaques were compared to previously reported findings in spontaneously resolving guttate lesions, and the effects of PUVA treatment on these cell populations studied. The chronic lesions showed a similar T helper/T suppressor (TH/TS) ratio (0.66 +/- 0.10) to resolving guttate lesions. However, in contrast to the resolving lesions which do not contain activated epidermal TH cells, a substantial proportion of the TH cells in the persistent plaques were DR+. Moreover, these persistent lesions contained markedly increased numbers of DR+ dendritic cells, approximately 20% of which were T6 negative. PUVA-induced resolution of chronic lesions was associated with depletion of epidermal TH and TS cells, and a subsequent reduction in DR+ dendritic cells. In each patient the rate of disappearance of both cell types correlated with the rate of resolution. Furthermore, the epidermal T cell depletion preceded the onset of clinical improvement. In contrast, significant reduction of the dendritic cells was generally not observed until the lesions were largely resolved. Dendritic cells decreased faster in uninvolved than in lesional skin and to a subnormal level. Dermal T cells also decreased during PUVA therapy but this did not show any obvious correlation with resolution of the lesions. Blood T cell levels were not significantly affected by the treatment. These findings support the concept that the initiation and maintenance of the psoriatic process requires activation of TH cells in the epidermis via interaction with antigen presenting cells. Furthermore PUVA treatment may clear psoriasis by interfering with such a mechanism through its effects on T lymphocytes.     

T lymphocytes targeting native receptors

The adoptive transfer of T cells specific for native tumor antigens (TAs) is an increasingly popular cancer treatment option because of the ability of these cells to discriminate between normal and tumor tissues and the corresponding lack of short or long-term toxicities. Infusions of antigen-specific CD4⁺ and CD8⁺ T cells targeting viral antigens derived from Epstein–Barr virus (EBV) induce sustained complete tumor remissions in patients with highly immunogenic tumors such as post-transplant lymphoproliferative disease, although resistance occurred when the infused T-cell population had restricted antigen specificity. T cells specific for EBV antigens have also produced complete remissions of EBV-positive nasopharyngeal carcinomas and lymphomas developing in immunocompetent individuals, even though in these patients tumor survival is dependent on their ability to evade T-cell immunity. Adapting this strategy to non-viral tumors is more challenging, as the target antigens expressed are less immunogenic and the tumors lack the potent danger signals that are characteristic of viruses. The goals of current studies are to define conditions that promote expansion of antigen-specific T cells ex vivo and to ensure their in vivo persistence and survival by combining with maneuvers such as lymphodepletion, checkpoint inhibition, cytokine infusions, or genetic manipulations. More pragmatic goals are to streamline manufacturing to facilitate the transition of these therapies to late phase trials and to evaluate closely histocompatibility antigen (HLA)-matched banked antigen-specific T cells so that T-cell therapies can be made more broadly available.     

High frequency of memory and effector gag specific cytotoxic T lymphocytes in HIV seropositive individuals

Human immunodeficiency virus type 1 (HIV-1) specific cytotoxic T lymphocytes (CTL) have been detected in most patients following infection. It has also been suggested that the specific CTL response, which may play an important role in delaying disease in infected humans, may decline during the course of disease progression. We have measured HIV peptide specific CTL precursor frequency by limiting dilution analysis in two healthy seropositive patients whose fresh peripheral blood mononuclear cells (PBM) specifically lysed MHC matched target cells (restricted by HLA B27 and B8 respectively). The frequency of HIV peptide specific CTL precursors is high (3 x 10(-3)-10(-4], but lower than estimates of circulating CTL with the same specific cytotoxic activity present directly in peripheral blood using the same sample (10(-2)-10(-3]. We suggest that this difference may result from terminal effector CTL differentiation in the T cell lineage. This implies that only a subset of CTL effectors have growth potential, whereas relatively higher levels of CTL with lytic activity can be detected in PBM of healthy HIV seropositive patients.     

Non-replicating adenovirus vectors expressing avian influenza virus hemagglutinin and nucleocapsid proteins induce chicken specific effector, memory and effector memory CD8 T lymphocytes

Avian influenza virus (AIV) specific CD8⁺ T lymphocyte responses stimulated by intramuscular administration of an adenovirus (Ad) vector expressing either HA or NP were evaluated in chickens following ex vivo stimulation by non-professional antigen presenting cells. The CD8⁺ T lymphocyte responses were AIV specific, MHC-I restricted, and cross-reacted with heterologous H7N2 AIV strain. Specific effector responses, at 10 days post-inoculation (p.i.), were undetectable at 2 weeks p.i., and memory responses were detected from 3 to 8 weeks p.i. Effector memory responses, detected 1 week following a booster inoculation, were significantly greater than the primary responses and, within 7 days, declined to undetectable levels. Inoculation of an Ad-vector expressing human NP resulted in significantly greater MHC restricted, activation of CD8⁺ T cell responses specific for AIV. Decreases in all responses with time were most dramatic with maximum activation of T cells as observed following effector and effector memory responses.     

Inhibition of cell-mediated lysis by xenoantibodies reactive with effector T lymphocytes

The aim of the present study was to determine whether rabbit antisera against various murine tissue antigens contain antibodies that affect the activity of cytotoxic T lymphocytes in the absence of complement. Following heat inactivation, the xenoantisera were absorbed with mouse liver and kidney and tested for their capacity to inhibit cell-mediated lysis (CML). In the presence of complement (C), rabbit anti-brain antiserum (RABr), rabbit anti-thymus antiserum (RAT) and rabbit anti-boiled thymus antiserum (RABT) lysed effector T cells, and CML was abolished. In the absence of C, RAT maintained its strong inhibitory activity on CML, RABr had no inhibitory effect, whereas only some batches of RABT were effective. Monovalent Fab fragments of RAT inhibited CML as effectively as intact antibody molecules. The activity of RAT could be removed by absorption with T and B lymphocytes of various sources. Inhibitory antibodies could be removed by absorption with C3 H B lymphoma cells and upon elution from antibody-coated cells proved again highly effective in inhibiting CML. These results show that RAT contains antibodies which react with determinants shared by T and B lymphocytes and which block the activity of cytotoxic T cells.     

Stronger proliferative response to membrane versus cell-wall Streptococcal proteins by peripheral blood T cells in chronic plaque psoriasis

Proliferative responses of peripheral blood mononuclear cells (PBMC) to group A streptococcal (GAS) antigens have been studied in 24 patients with psoriasis and 15 disease controls. Extracts of cell wall (including M protein) from types M4 and M12 GAS, recombinant M6 protein, and both cell-wall and cell-membrane extracts from type M6 (M6+) GAS and its corresponding M gene deletion mutant (M6-) were tested. PBMC from psoriatic patients proliferated more strongly to cell-wall extracts from M12 versus M4 (P = 0.0348), and to M6+ versus M6- (P = 0.0019) GAS with, in most cases, moderate proliferation to recombinant M6 protein. The psoriatic response to M12 cell wall was significantly increased compared to the controls (P = 0.0032). In psoriatics, M6+ membrane extracts induced a markedly greater proliferation than those of cell wall (P = 0.0002); responses to M6+ (P = 0.0039) and M6- (P = 0.0114) membrane extracts were higher than those of the control PBMC. Both groups showed a decreased response to the M6- versus M6+ membrane extracts (P = 0.0030; P = 0.0181, respectively). This study has demonstrated that patients with psoriasis have a heightened circulating T-cell response to cell wall M protein and to non-M proteins present on the cell wall and membrane of GAS.     

Recruitment of effector lymphocytes by initiator lymphocytes. In vivo migration of in vitro sensitized initiator T lymphocytes

We previously found that mouse T lymphocytes sensitized in vitro against allo- or syngeneic fibroblasts, upon injection into syngeneic recipients, do not themselves differentiate into effector cells, but recruit effector T lymphocytes within the draining lymph nodes. Asaresult of sensitization, these initiator lymphocytes acquire a trypsin-sensitive membrane property which is necessary for recruitment. We now report studies on the in vivo migratory behavior of initiator lymphocytes following sensitization. We injected ⁵¹Cr-labeled initiator lymphocytes into recipient footpads and found significantly increased migration of sensitized cells to the draining popliteal lymph node (PLN) during the first day. By amputation ofthe foot at various times, we showed that migration during the first 12—24 hours was critical for subsequent recruitment. Trypsin treatment of initiator lymphocytes abolished this accelerated migration. Lymphocytes triggered nonspecifically by Con A migrated to the PLN like antigen-sensitized cells. We also compared the migration of injected lymphocytes from the footpad to the PLN in graftversus-host and host-versus-graft reactions, and found these reactions to differ both from each other and from recruitment in terms of lymphocyte migration. These findings are discussed in terms of the physiology of the cell-mediated immune response and the notion of peripheral sensitization.     

Characterization of a subset of antigen-specific human central memory CD4+ T lymphocytes producing effector cytokines

CCR7(+ )central memory (T(CM)) CD4(+) T cells play a central role in long-term immunological memory. Recent reports indicate that a proportion of CD4(+) T(CM) is able to produce effector cytokines. The phenotype and the role of this subset remain unknown. We characterized cytokine-producing human CD4(+) T(CM) specific for cleared protein and persistent viral Ag. Our results demonstrate that the type of Ag stimulation is a major determinant of CD4(+) T(CM) differentiation. CMV-specific T(CM) were significantly more differentiated than protein Ag-specific T(CM) and included higher proportions of IFN-gamma-producing cells. The expression of killer cell lectin-like receptor G1 (KLRG1) by protein Ag- and CMV-specific T(CM) was associated with increased production of effector cytokines. KLRG1(+) T(CM) expressed high levels of CD127, suggesting that they can survive long term under the influence of IL-7. The induction of KLRG1(+) T(CM) may therefore represent an important target of vaccination against pathogens controlled by cellular immune responses.     

Expression of CD8alpha identifies a distinct subset of effector memory CD4+ T lymphocytes

Circulating CD4+ CD8+ T lymphocytes have been described in the peripheral blood of humans and several animal species. However, the origin and functional properties of these cells remain poorly understood. In the present study, we evaluated the frequency, phenotype and function of peripheral CD4+ CD8+ T cells in rhesus macaques. Two distinct populations of CD4+ CD8+ T cells were identified: the dominant one was CD4hi CD8lo and expressed the CD8alphaalpha homodimer, while the minor population was CD4lo CD8hi and expressed the CD8alphabeta heterodimer. The majority of CD4hi CD8alphalo T cells exhibited an activated effector/memory phenotype (CCR5lo CD7- CD28- HLA-DR+) and expressed relatively high levels of granzyme B. Intracellular cytokine staining assays demonstrated that the frequency of cytomegalovirus-specific T cells was enriched five-fold in CD4hi CD8alphalo T cells compared to single-positive CD4+ T cells, whereas no consistent enrichment was observed for simian immunodeficiency virus (SIV)-specific T cells. Cross-sectional studies of SIV-infected animals demonstrated that the frequency of CD4hi CD8alphalo T cells was lower in wild-type SIV-infected animals compared to uninfected controls, although prospective studies of SIV-infected animals demonstrated depletion of CD4hi CD8alphalo lymphocytes only in a subset of animals. Taken together, these data suggest that CD4+ T cells expressing CD8alpha represent an effector/memory subset of CD4+ T cells and that this cell population can be depleted during the course of SIV infection.     

Ultraviolet B suppresses immunity by inhibiting effector and memory T cells

Contact hypersensitivity is a T-cell-mediated response to a hapten. Exposing C57BL/6 mice to UV B radiation systemically suppresses both primary and secondary contact hypersensitivity responses. The effects of UVB on in vivo T-cell responses during UVB-induced immunosuppression are unknown. We show here that UVB exposure, before contact sensitization, inhibits the expansion of effector CD4+ and CD8+ T cells in skin-draining lymph nodes and reduces the number of CD4+ and IFN-gamma+ CD8+ T cells infiltrating challenged ear skin. In the absence of UVB, at 10 weeks after initial hapten exposure, the ear skin of sensitized mice was infiltrated by dermal effector memory CD8+ T cells at the site of challenge. However, if mice were previously exposed to UVB, this cell population was absent, suggesting an impaired development of peripheral memory T cells. This finding occurred in the absence of UVB-induced regulatory CD4+ T cells and did not involve prostaglandin E2, suggesting that the importance of these two factors in mediating or initiating UVB-induced immunosuppression is dependent on UVB dose. Together these data indicate that in vivo T-cell responses are prone to immunoregulation by UVB, including a novel effect on both the activated T-cell pool size and the development of memory T cells in peripheral compartments.     

Recruitment of effector lymphocytes by initiator lymphocytes. In vivo migration of in vitro sensitized initiator T lymphocytes.

We previously found that mouse T lymphocytes sensitized in vitro against allo- or syngeneic fibroblasts, upon injection into syngeneic recipients, do not themselves differentiate into effector cells, but recruit effector T lymphocytes within the draining lymph nodes. As a result of sensitization, these initiator lymphocytes acquire a trypsin-sensitive membrane property which is necessary for recruitment. We now report studies on the in vivo migratory behavior of initiator lymphocytes following sensitization. We injected 51Cr-labeled initiator lymphocytes into recipient footpads and found significantly increased migration of sensitized cells to the draining popliteal lymph node (PLN) during the first day. By amputation of the foot at various times, we showed that migration during the first 12-24 hours was critical for subsequent recruitment. Trypsin treatment of initiator lymphocytes abolished this accelerated migration. Lymphocytes triggered nonspecifically by Con A migrated to the PLN like antigen-sensitized cells. We also compared the migration of injected lymphocytes from the footpad to the PLN in graft-versus-host and host-versus-graft reactions, and found these reactions to differ both from each other and from recruitment in terms of lymphocyte migration. These findings are discussed in terms of the physiology of the cell-mediated immune response and the notion of peripheral sensitization.     

NKT cells: T lymphocytes with innate effector functions

Natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens in the context of the MHC class I-related glycoprotein CD1d. Recent studies have identified multiple ways in which NKT cells can become activated during microbial infection. Mechanisms of CD1d-restricted antigen presentation are being unraveled, and a surprising connection has been made to proteins that control lipid metabolism and atherosclerosis. It appears that several microorganisms have developed strategies to interfere with the CD1d antigen-presentation pathway. New studies have also provided important insight into the mechanisms that control effector cell differentiation of NKT cells and have revealed specialized functions of distinct NKT cell subsets. Finally, there is continued enthusiasm for the development of NKT cell-based therapies of human diseases.     

Local development of effector and memory T helper cells

Clonal evolution underpins all facets of adaptive immunity. In particular, antigen-specific helper T (Th) cell development is central to high-affinity B cell immunity and protective vaccination. Dendritic cell maturation and TCR affinity-based selection mechanisms control the recruitment and effective propagation of preferred antigen-specific Th cell cohorts in local lymphoid tissue. Importantly, follicular B helper T (T(FH)) cells emerge as the specialized local effector Th cells that orchestrate the stepwise development of B cell immunity in these local environments. Recent studies also introduce the role of persistent antigen in the development of effector Th cells with evidence for long-term antigen depots that might contribute to local antigen-specific Th cell memory.     

Altered claudin expression is a feature of chronic plaque psoriasis

Epithelial tight junctions play a central role in cell-cell adhesion and are necessary for the selective paracellular movement of ions. Claudins are key components of tight junctions and their expression is altered in gut epithelia in a variety of inflammatory enteropathies, including ulcerative colitis and Crohn's disease. Psoriasis is a chronic inflammatory skin disease affecting approximately 2% of the western population, with significantly increased occurrence in individuals with Crohn's disease. Initial studies investigated the expression of claudins in skin of healthy volunteers and patients with chronic plaque psoriasis. We report here that claudins-1 and -3 are the major protein species present in the epidermis of healthy skin; they are expressed on the surface of epidermal keratinocytes, consistent with their localization to tight junctions. In plaques of psoriasis, claudin-1 was not identifiable in the epidermis, although typical staining patterns were observed in clinically normal, uninvolved skin of patients with psoriasis. Claudin-3 was present in the epidermal granular cell layer in normal skin, but was only identified within the cytosol of epidermal keratinocytes in both involved and uninvolved skin of psoriasis patients. We examined further whether exposure of keratinocytes in vitro to pro-inflammatory cytokines mimicked the observed changes in claudin expression seen in chronic plaque psoriasis; lipopolysaccharide, interferon-gamma and tumour necrosis factor-alpha had no effect on claudin protein expression or distribution. Addition of interleukin-1beta, however, resulted in down-regulation of claudins-1 and -3. Tumour necrosis factor-alpha and interleukin-1beta were further used in an in vivo model of skin inflammation; interleukin-1beta alone modulated claudin protein expression in this system. These data demonstrate that epidermal claudin expression is altered in chronic plaque psoriasis and that expression is in part modulated by interleukin-1beta.     

Induction of memory and effector suppressor T cells by perinatal exposure to antigen

The development of tolerance and suppression after perinatal exposure to antigen was studied to clarify the role of suppressor cells in self tolerance. Deaggregated human gamma globulin (dHGG) was administered transplacentally to fetal mice by injecting their mothers at various stages of pregnancy. Other mice were exposed to dHGG present in the colostrum of foster mothers previously injected with dHGG. Nonspecific suppression was seen on adoptive transfer of spleen cells from all donors less than six weeks of age. After that time, HGG-specific primary suppression by Ly1^?2,3⁺Ia⁺ T cells was detected in all animals exposed to dHGG either pre- or postnatally and persisted for up to three months. In addition, recall of specific memory suppression by antigen challenge was demonstrable for up to six months. Tolerance, on the other hand, was generated only by higher doses of dHGG in utero and was relatively short-lived when compared to suppression. The short duration of tolerance could not be attributed to the generation of T helper cells, since no significant HGG-specific helper activity was detected after perinatal exposure to HGG; rather it was thought to be due to the failure of small doses of dHGG to generate sufficient effector T suppressor (T_s) cells to inactivate the continually increasing number of HGG-specific B cells being generated during ontogeny. Since perinatal tolerance to HGG is known to be prolonged by repeated exposure to antigen, this model implies that the maintenance of natural self tolerance is T_s cell dependent and requires the continued presence of antigen.