Differential expression of CD40 ligand on T cell subsets. Implications for different roles of CD45RA+ and CD45RO+ cells in IgE production

Physical contact between human T lymphocytes and B lymphocytes is required for the induction of IgE production. In the present study, we examined the abilities of CD45RA+ and CD45RO+ human T cell subsets to provide help for IgE production by human peripheral blood B cells in the presence of IL-4. Purified peripheral CD45RA+ T cells are much better inducers of IgE synthesis than are CD45RO+ T cells. Activation of CD45RA+ T cells, but not CD45RO+ T cells, via the TCR/CD3 complex is sufficient to confer the ability to provide IgE help, suggesting that an inducible T cell surface molecule plays an important role in this system. The CD40 ligand, an inducible T cell surface molecule, is expressed at higher levels on CD45RA+ T cells as compared with CD45RO+ T cells following CD3-stimulation. Blocking of the CD40-CD40 ligand interaction in vitro by the addition of a soluble form of B cell CD40 Ag completely blocks IgE production induced by CD45RA+ T cells. Finally, the in vitro conversion of CD45RA+ T cells to the CD45RO+ phenotype is accompanied by a loss in the ability of these cells to express the CD40 ligand in response to anti-CD3 stimulation as well as a loss in their ability to provide IgE help. These results suggest that both CD45 subsets may play significant and distinct roles in the induction of IgE production under physiologic conditions: CD45RO+ T cells provide IL-4 and the CD45RA+ subset provides the second signal via the CD40 ligand.     

Age-related increase in the fraction of CD27-CD4+ T cells and IL-4 production as a feature of CD4+ T cell differentiation in vivo

The influence of ageing on phenotype and function of CD4+ T cells was studied by comparing young (19-28 years of age) and aged (75-84 years of age) donors that were selected using the SENIEUR protocol to exclude underlying disease. An age-related increase was observed in the relative number of memory cells, not only on the basis of a decreased CD45RA and increased CD45RO expression, but also on the basis of a decrease in the fraction of CD27+CD4+ T cells. Our observation that the absolute number of CD45RO+CD4+ T cells was increased, while absolute numbers of CD27-CD4+ T cells remained unchanged in aged donors, indicates that the latter subset does not merely reflect the size of the CD45RO+CD4+ T cell pool. The increased fraction of memory cells in the aged was functionally reflected in an increased IL-4 production and T cell proliferation, when cells were activated with the combination of anti-CD2 and anti-CD28, whereas IL-2 production was comparable between both groups. No differences were observed with respect to proliferative T cell responses or IL-2 production using plate-bound anti-CD3 or phytohaemagglutinin (PHA). The observation that IL-4 production correlated with the fraction of memory cells in young donors but not in aged donors suggests different functional characteristics of this subset in aged donors.     

Evidence for selective in vivo expansion of synovial tissue-infiltrating CD4+ CD45RO+ T lymphocytes on the basis of CDR3 diversity

In this study we have analyzed the TCR V alpha and V beta regions at the DNA level in the CD4+CD45RO+ memory T cell population of synovial tissue infiltrating T lymphocytes of three rheumatoid arthritis (RA) patients and one patient with chronic arthritis. Cell lines of CD4+CD45RO+, CD4+CD45RO-, CD8+CD45RO+ and CD8+CD45RO- T lymphocyte populations were generated following FACS cell sorting of freshly isolated synovial tissue mononuclear cell infiltrates (STMC) and of freshly isolated peripheral blood mononuclear cells (PBMC) of these patients. The phenotypic and molecular analyses have revealed the following. (i) The TCR repertoires of tissue infiltrating T lymphocytes in the various subsets were extensive on the basis of TCR V gene family usage. (ii) Furthermore, each patient displayed individual specific TCR V gene expression patterns in the various STMC and PBMC derived T cell subsets. However, the majority of these arthritis patients manifested increased expression of multiple TCR V gene families in the synovial tissue derived CD4+CD45RO+ T cell population when compared with the peripheral blood derived CD4+CD45RO+ subset. Of these gene families, we found enhanced expression of the TCR V alpha 7 and V beta 11 gene segments in synovial tissue to be shared by all four patients analyzed. (iii) Nucleotide sequence analysis of the CDR3 regions of a number of TCR V regions in the CD4+CD45RO+ T cell subsets has revealed that the CDR3 regions comprised within synovial tissue derived TCR V regions differed from those found in peripheral blood derived TCR V regions. These differences in CDR3 diversity might be the consequence of a specific interaction with particular MHC-peptide complexes expressed at the site of inflammation. (iv) The CDR3 region analysis also showed individual specific amino acid motifs within the N-D-N regions of all analyzed TCR V beta genes derived from PBMC as well as STMC.     

T cell responses to heat-shock protein 60: differential responses by CD4+ T cell subsets according to their expression of CD45 isotypes

We demonstrate that human T lymphocytes proliferate in vitro to highly purified human heat-shock protein 60 (Hu.hsp60). The response to this self Ag was confined to the CD45RA+ RO- T cell subset, with minimal responses by adult CD45RA- RO+ T cells. Experiments using keyhole limpet hemocyanin as a prototypic novel Ag, or tetanus toxoid as a recall Ag, were consistent with the notion that CD45RA+ RO- and CD45RA- RO+ T cell subsets can be designated as naive and memory cells, respectively; thus, responses to Hu.hsp60 were confined to the putative naive subset. In contrast, both CD45RA+ RO- and CD45RA- RO+ T cell populations proliferated to bacterial hsp60 from Mycobacterium leprae, Escherichia coli, or Chlamydia trachomatis. However, only CD45RA- RO+ (memory) T cells responded to a mycobacterial hsp60-derived peptide previously defined as a major bacteria-specific epitope. Experiments with cord blood T cells, which are CD45RA+ RO- and can be considered truly naive, showed that the peptide could elicit responses from naive T cells in vitro; cord blood cells also responded to Hu.hsp60. Since bacterial hsp60 Ags contain both conserved and nonconserved epitopes, we speculate that in vivo challenge with bacterial hsp60 will activate T cells capable of seeing either type of epitope, but only those that see nonconserved epitopes maintain the CD45RA- RO+ memory phenotype. However, T cells recognizing conserved epitopes, while not apparently being recruited to the memory pool, may nevertheless play a role in immunoregulation, particularly in the context of inflammation, when expression of Hu.hsp60 is increased.     

Increase in adhesion molecules on CD4+ cells and CD4+ cell subsets in synovial fluid from patients with rheumatoid arthritis

OBJECTIVE: To elucidate the role of adhesion molecules in the pathogenesis of rheumatoid arthritis (RA). METHODS: We evaluated their expression and that of an activation marker on CD4+ cell populations and CD4+ cell subsets in specimens of peripheral blood (PB) and synovial fluid (SF) obtained from 10 patients with RA and 7 with osteoarthritis (OA). A 2 or 3-color immunofluorescent method was used for analysis. RESULTS: The SF from both groups of patients showed a greater density of adhesion molecules including LFA-1 alpha, LFA-1 beta, CD2, VLA-4 alpha and VLA-5 alpha on CD4+ cells, and a higher percentage of CD4+HLA-DR+ cells compared with their PB. IN PB-CD4+ cell subsets from the arthritic and healthy subjects, the CD4+CD45RO+ cell population showed an increased expression of adhesion molecules compared with CD4+CD45RA+ cell population. The expression of adhesion molecules on circulating CD4+ cell population and CD4+ cell subsets from the patients with RA and OA was comparable to that from healthy subjects. SF from both groups of patients showed a higher percentage of CD4+CD45RO+ cells and a lower percentage of CD4+CD45RA+ cells. In SF-CD4+ cell subsets from patients with RA, the CD4+CD45RO+ cell population had an increased expression of VLA-4 alpha compared to the CD4+CD45RA+ cell population; however, there was no significant difference in other adhesion molecule expression and the percentage of HLA-DR+ cells between the 2 cell subsets. Furthermore, the expression of VLA-4 alpha on the CD4+CD45RO+ cell population in SF from patients with RA was significantly higher than that in matched PB. In CD4+CD45RA+ cell population from both groups of patients, SF showed an enhanced expression of adhesion molecules and an increased percentage of HLA-DR+ cells compared with matched PB. CONCLUSION: Our results suggest that increased expression of adhesion molecules and increased percentage of HLA-DR+ cells on CD4+ cells in SF may be responsible for cellular interactions between these cells and synovial cells or extracellular matrix.     

Demonstration of identical expanded clones within both CD8+CD28+ and CD8+CD28- T cell subsets in HIV type 1-infected individuals

In HIV-1-infected individuals, the CD8+CD28- T cell subset is considerably expanded and is frequently the largest subset of T cells found in peripheral blood. It has been assumed, but not proven, that CD8+CD28- T cells derive from CD8+CD28+ T cells in vivo. To further study the ontogeny of CD8+CD28- T cells, we have performed analyses of the complementarity determining region 3 (CDR3) of the TCRB of CD8+CD28+ and CD8+CD28- T cells from the peripheral blood of HIV-1-infected individuals. When cells from the same individual were compared, expanded peaks in CDR3 length analysis within a given BV family were frequently observed at the same location in both CD8+ subsets (p < 0.001). Sequencing of cDNA corresponding to dominant peaks revealed the presence of identical expanded CD8+ T cell clones within both the CD28+ and CD28- subsets on eight of nine attempts. Our results show that CD8+CD28+ and CD8+CD28- T cells are phenotypic variants of the same lineage, most likely evolving from CD8+CD28+ to end-stage CD8+CD28- T cells.     

Interleukin-12 primes human CD4 and CD8 T cell clones for high production of both interferon-gamma and interleukin-10

Interleukin-12 (IL-12) induces differentiation of T helper 1 (Th1) cells, primarily through its ability to prime T cells for high interferon-gamma (IFN-gamma) production. We now report that the presence of IL-12 during the first several days of in vitro clonal expansion in limiting dilution cultures of polyclonally stimulated human peripheral blood CD4+ and CD8+ T cells also induces stable priming for high IL-10 production. This effect was demonstrated with T cells from both healthy donors and HIV+ patients. Priming for IL-4 production, which requires IL-4, was maximum in cultures containing both IL-12 and IL-4. IL-4 modestly inhibited the IL-12-induced priming for IFN-gamma, but almost completely suppressed the priming for IL-10 production. A proportion of the clones generated from memory CD45RO+ cells, but not those generated from naive CD45RO- CD4+ T cells, produced some combinations of IFN-gamma, IL-10, and IL-4 even in the absence of IL-12 and IL-4, suggesting in vivo cytokine priming; virtually all CD4+ clones generated from either CD45RO(-) or (+) cells, however, produced high levels of both IFN-gamma and IL-10 when IL-12 was present during expansion. These results indicate that each Th1-type (IFN-gamma) and Th2-type (IL-4 and IL-10) cytokine gene is independently regulated in human T cells and that the dichotomy between T cells with the cytokine production pattern of Th1 and Th2 cells is not due to a direct differentiation-inducing effect of immunoregulatory cytokines, but rather to secondary selective mechanisms. Particular combinations of cytokines induce a predominant generation of T cell clones with anomalous patterns of cytokine production (e.g., IFN-gamma and IL-4 or IFN-gamma and IL-10) that can also be found in a proportion of fresh peripheral blood T cells with "memory" phenotype or clones generated from them and that may identify novel Th subsets with immunoregulatory functions.     

The levels of memory (CD45RA-, RO+) CD4+ and CD8+ peripheral blood T-lymphocytes correlate with IgM rheumatoid factors in rheumatoid arthritis

We investigated whether, in rheumatoid arthritis (RA), the CD45 isoform expression of peripheral blood T-lymphocytes (T-PBL) is related to auto-immune processes (e.g. IgM rheumatoid factors) and to clinical manifestations. By three-colour flow cytometry, we quantified three subsets of CD4+ or CD8+ T-PBL: "naive" CD45RA+,RO-, "transient" CD45RA+,RO+, and "memory" CD45RA-,RO+ cells, in 102 patients with RA and in 41 age- and sex-matched controls. The serum levels of rheumatoid factors (RF) were determined--besides conventional agglutination tests--by ELISA (IgM-RF). Extensive clinical examination was performed at the time of blood sampling. In RA, age, sex and drug therapy did not constitute major influences on the CD45RA/RO patterns. In "healthy" men, higher age significantly' correlated with fewer naive and more memory CD4+ T-PBL (P < 0.01). In RA, distinct correlations between the T-PBL subsets, autoimmune and clinical manifestations became obvious when patients with low and high levels of RF against human IgG Fc fragments, as determined by ELISA, were analysed separately. RA patients with high IgM-RF had elevated proportions of CD45RO+ T-PBL (P < 0.05), that correlated with clinical parameters of disease activity (tender joint count, Ritchie index, P < 0.05) and outcome (Health Assessment Questionnaire, Larsen radiographic scores, P < 0.05). The proportions of memory CD4+ and CD8+ T-PBL correlated strongly (P < 0.001) with the IgM-RF levels. Within 1 year, only three of 34 patients (disease duration of 5-9 years) showed seroconversion from low to high levels of IgM-RF (and positive agglutination tests); this was paralleled by reductions in naive and increases in transient T-PBL (P < 0.02). Thus, in RA, the proportions of memory CD4+ and CD8+ T-PBL correlate with the level of IgM-RF and, together with transient T-PBL, with clinical parameters of disease activity and outcome.     

Regulation of CD27 expression on subsets of mature T-lymphocytes

CD27, a lymphocyte-specific member of the TNF/NGF-R family, is expressed on the majority of peripheral blood T cells. Activation of T cells via TCR/CD3 induces high CD27 surface expression and the release of a soluble extracellular part of the molecule. After prolonged activation in vitro, CD27 becomes gradually switched off. There is evidence that also in vivo, CD4+ cells that have persistently been stimulated by Ag, accumulate within the CD45RA-CD27- subset. In addition, an increase of CD27- T cells has been observed under certain immunopathologic conditions and during aging. This study was undertaken to analyze the regulation of CD27 on different T-cell subsets and to determine whether the loss of CD27 expression is an irreversible event and may thereby mark T-cell differentiation. In agreement with earlier findings, all CD4+CD45RA+CD45RO- T cells were found to express CD27, whereas a small fraction of the CD4+CD45RA-CD45RO+ subset lacks the molecule. In contrast, within the CD8+ compartment CD27- subsets were found both in the CD45RA+ and CD45RA- subpopulations. After stimulation with CD3 mAb, both CD27 membrane expression and release was equally up-regulated in CD4+ and CD8+ subpopulations. This stimulus, however, provoked a strikingly predominant up-regulation of membrane CD27 on CD45RO- cells as compared with CD45RA- cells. On CD4+CD45RA-CD27- T cells and long-term grown CD45RA-CD27- TLC, CD27 expression could not be reinduced after stimulation of the TCR/CD3 complex, neither at the protein nor at the mRNA level. Comparison of CD27 expression with its structural homologue FAS/APO-1 showed that down-regulation after prolonged activation is not a general feature of TNF/NGF-R family members. The CD27 ligand was recently identified and was shown to give a co-stimulatory signal to PHA-activated T cells. The restricted up-regulation of CD27 on CD45RA+ cells after T-cell stimulation may point at a discrete role of CD27-CD27 ligand interaction during transition of CD45RO- to CD45RA- T cells. In addition, the CD27 negative phenotype seems a stable reflection of differentiation rather than of activation.     

Characterization of circulating CD4+ CD8+ lymphocytes in healthy individuals prompted by identification of a blood donor with a markedly elevated level of CD4+ CD8+ lymphocytes

During flow cytometric analysis of lymphocytes from healthy donors, we identified a donor (donor A) with 22% CD4+ CD8+ cells (versus values of < 4% for 65 other controls). To determine if CD4+ CD8+ cells from donor A and other controls were similar, we first defined the phenotypic profile of control CD4+ CD8+ cells. Enriched CD4+ CD8+ cell populations for 10 controls were prepared by a two-step positive selection scheme with anti-CD4-coated magnetic beads and anti-CD8-coated culture flasks; the selected population averaged 69% CD4+ CD8+ cells and 31% CD4+ CD8- cells. For all 10 controls, two subsets of CD4+ CD8+ cells, CD4dim CD8bright and CD4bright CD8dim, were observed. Phenotypic profiles of these two CD4+ CD8+ subsets were defined by pairing anti-CD8 with other monoclonal antibodies, and the profiles were compared with each other and with those of CD4+ CD8-, CD4- CD8bright, and CD4- CD8dim cells. CD8bright and CD4bright CD8dim cells differed in their proportions of CD62-L+ cells and in their levels of CD11a and CD2 expression. Both CD4+ CD8+ subsets resembled CD4+ CD8- cells in CD45RA, CD45RO, and CD25 expression; the comparable CD- CD8+ cells in CD62-L expression; and CD4- CD8bright cells in CD11b, CD11b, CD16/56, and CD28 expression. CD38 expression in both CD4+ CD8+ subsets was decreased compared with those of other cell subsets. Whereas control CD4+ CD8+ cells averaged 33% CD4dim CD8bright, CD4+ CD8+ cells from donor A were > 90% CD4dim CD8bright. Donor A CD4dim CD8bright cells exhibited proportional decreases in CD25 and CD62-L expression and increases in CD11b and CD54 expression compared with those of control CD4dim CD8bright cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Redox regulation of ubiquitin-conjugating enzymes: mechanistic insights using the thiol-specific oxidant diamide

This study explores whether previous failures on antiretroviral drug regimens preclude the possibility of immune restoration. This was assessed by evaluating T cell subset changes in individuals who received a salvage regimen of highly active antiretroviral therapy (HAART) after initially failing protease inhibitor monotherapy. Ten HIV-1-infected asymptomatic patients received a regimen of indinavir, zidovudine, and 3TC after failing saquinavir monotherapy. Changes in absolute numbers of naive, memory, and activated CD4+ and CD8+ T cells expressing a selection of CD45RA, CD62L, CD45RO, HLA-DR, and CD38 markers were monitored prospectively over 6 months. These measurements were correlated with plasma viral load along with alterations in a selected CD8+ V alpha/Vbeta T cell receptor (TCR) repertoire. Over 6 months there was a progressive increase in numbers of CD4+ memory (CD45RA-CD62L+) and naive (CD45RA+CD62L+) T cells, which displayed a modest inverse correlation with viral load. Two phases of CD8+ memory cell changes were identified, consisting of a transient increase in CD45RA+CD62L- numbers after 2 months and thereafter a progressive rise in CD45RA-CD62L+ cells until 6 months. A strong correlation existed between reduced viral load and loss of activated CD8+CD38+HLA-DR+ cell numbers. There was also a temporary broadening of the CD8+ V alpha/Vbeta TCR repertoire at 8 weeks, which became skewed after 6 months in parallel with reduced viral suppression. Closer analysis of naive and memory cell subset proportions in individual patients revealed that enlarged pools of naive subsets were evident in those patients with rebounds in viral load. Overall, drug-experienced patients responding to HAART displayed increased numbers of naive and memory CD4+ subsets, and reduced CD8+ cell activation with a loss of TCR skewing.     

Coexpression of GD3 ganglioside with CD45RO in resting and activated human T lymphocytes

The ganglioside GD3 is preferentially expressed on the surface of malignant T cell lymphoblasts and on resting T cells which express the memory cell phenotype, CD45RA-CD29+. However, GD3 expression in activated T cells and its potential function in proliferating normal and malignant T cells are unclear. Utilizing three-color immunostaining and flow cytometry, we examined changes in the expression of GD3 in conjunction with the RA and RO isoforms of CD45 during in vitro T cell activation. GD3 was equally expressed in resting CD4 and CD8 cells and was specifically found in the CD45RO+RA population. Activation of T cells with PHA resulted in an increased percentage of GD3+ cells. This increase was evident by the first day and was observed in the CD45RO (naive cell) population; by 2 days, GD3 was expressed heterogeneously in a large population of CD45RO+RA+ cells. Further activation of T cells with PHA or anti-CD3 monoclonal antibody (OKT3) resulted in a further increase in GD3-expressing cells, and the increase in GD3 density correlated with increased CD45RO and loss of CD45RA. In contrast, increases in GD3 and interleukin-2 receptor (CD25) expression in response to PHA or OKT3 occurred independently, indicating that the GD3/ CD45RO coexpression observed was not a general consequence of cell activation. The results provide evidence for specific comodulation of GD3 and CD45RO during T cell mitogenesis, and thus suggest that these molecules may colocalize on the T cell surface.     

Dominant clonotypes in the repertoire of peripheral CD4+ T cells in rheumatoid arthritis

Clonal expansion of T cell specificities in the synovial fluid of patients has been taken as evidence for a local stimulation of T cells. By studying the T cell receptor (TCR) repertoire of CD4+ T cells in the synovial and peripheral blood compartments of patients with early rheumatoid arthritis (RA), we have identified clonally expanded CD4+ populations. Expanded clonotypes were present in the peripheral blood and the synovial fluid but were not preferentially accumulated in the joint. Dominant single clonotypes could not be isolated from CD4+ cells of HLA-DRB1*04+ normal individuals. Clonal expansion involved several distinct clonotypes with a preference for V beta 3+, V beta 14+, and V beta 17+CD4+ T cells. A fraction of clonally related T cells expressed IL-2 receptors, indicating recent activation. The frequencies of clonally expanded V beta 17+CD4+ T cells fluctuated widely over a period of one year. Independent variations in the frequencies of two distinct clonotypes in the same patient indicated that different mechanisms, and not stimulation by a single arthritogenic antigen, were involved in clonal proliferation. These data support the concept that RA patients have a grossly imbalanced TCR repertoire. Clonal expansion may result from intrinsic defects in T cell generation and regulation. The dominance of expanded clonotypes in the periphery emphasizes the systemic nature of RA and suggests that T cell proliferation occurs outside of the joint.     

CD45RA(bright)/CD11a(bright) CD8+ T cells: effector T cells

An important aspect of peripheral T cell development is the differentiation from naive into memory cells. To distinguish naive from memory cells, CD45RA and CD11a are commonly used: CD45RA+ or CD11a(dim) T cells are regarded as naive, while CD45RA- or CD11a(bright) T cells are thought to be of memory type. There is, however, a CD8+ T cell subset which is CD45RA+ and at the same time CD11a(bright). It increases with age and in patients with systemic viral infections, though its functional role in the immune response is unknown. In the present study, we give evidence that this subset is related to memory-like T cells as it produces IFN-gamma and tumor necrosis factor-alpha, contains high levels of perforin, and expresses CD95 in the same way as memory-type CD45RA-/CD11a(bright) CD8+ T cells. Since it contains a high percentage of CD28- and CD57+ cells, is increased in size and granularity, and is transiently expressed following in vitro stimulation of naive CD8+ T cells, we speculate that this subset mainly represents recently activated effector T cells that are able to interact with CD80 and CD86 (B7-1 and B7-2 respectively) negative tissue cells.     

Direct visualization of antigen-specific CD8+ T cells during the primary immune response to Epstein-Barr virus In vivo

Primary infection with virus can stimulate a vigorous cytotoxic T cell response. The magnitude of the antigen-specific component versus the bystander component of a primary T cell response remains controversial. In this study, we have used tetrameric major histocompatibility complex-peptide complexes to directly visualize antigen-specific cluster of differentration (CD)8+ T cells during the primary immune response to Epstein-Barr virus (EBV) infection in humans. We show that massive expansion of activated, antigen-specific T cells occurs during the primary response to this virus. In one individual, T cells specific for a single EBV epitope comprised 44% of the total CD8+ T cells within peripheral blood. The majority of the antigen-specific cells had an activated/memory phenotype, with expression of human histocompatibility leukocyte antigen (HLA) DR, CD38, and CD45RO, downregulation of CD62 leukocyte (CD62L), and low levels of expression of CD45RA. After recovery from AIM, the frequency of antigen-specific T cells fell in most donors studied, although populations of antigen-specific cells continued to be easily detectable for at least 3 yr.     

Antigen presentation by epithelial cells induces anergic immunoregulatory CD45RO+ T cells and deletion of CD45RA+ T cells

The immunoregulatory effects of alloantigen presentation by tissue parenchymal cells to resting peripheral blood CD4+ T cells was investigated. Coculture of CD45RO+ (memory) and CD45RA+ (naive) T lymphocytes with primary cultures of MHC class II-expressing epithelial cells rendered both populations of T cells hyporesponsive to a subsequent challenge by the same MHC molecule expressed on EBV-transformed lymphoblastoid B cell lines. However, the mechanisms responsible for the allospecific hyporesponsiveness were distinct. For the CD45RO+ T cells, responsiveness was restored by subsequent culture in the presence of IL-2; the addition of IL-2 had no effect on the reactivity of the CD45RA+ T cells. In contrast, the naive T cells were protected from the induction of nonresponsiveness by the presence of a neutralizing anti-CD95 Ab during the culture with thyroid follicular cells. In addition, the hyporesponsive CD45RO+ T cells effected linked suppression, in that they inhibited proliferation against a third-party DR alloantigen when the third-party alloantigen was coexpressed with the DR Ag against which hyporesponsiveness had been induced. These results suggest that recognition of Ag by T cells on tissue parenchymal cells plays an important role in the maintenance of peripheral T cell tolerance, inducing nonresponsiveness in naive and memory T cells by distinct mechanisms.     

Age-related changes in the absolute number of CD95 positive cells in T cell subsets in the blood

Comparison of the absolute number of cells in distinct T cells subsets expressing CD95 (Fas) was carried out in two populations of healthy female volunteers. In one population, the average age was 30 +/- 5 years, and in the second population the average age was 73 +/- 13 years. No significant difference was noted in the total number of lymphocytes, CD3+, CD4+, or CD8+ cells per microL of blood between the two age groups, but major differences were noted in the number of cells expressing CD95. A significant reduction was seen in the number of cells per microL of blood in both the CD4+ CD45RA+ CD95+ and CD8+ CD45RA+ CD95+ populations in the older group compared with the younger group. Within the memory pool significantly fewer CD8+ CD45RO+ CD95+ cells were found in the older population compared with the younger group. No such difference were found in the number of CD4+ CD45RO+ CD95+ cells between groups. Such a significant decline in the number of CD95+ cells, whose expression is known to be linked with activation, may be implicated as a mechanism by which cells that have reached a stage of replicative senescence remain in the peripheral T cell pool. Anti-CD3-mediated activation of cells from both groups revealed much lower proliferative responses from the older group, supporting the idea that there is an age-associated increase in the number of cells that have reached their replicative limit. These cells may not be lost from the peripheral pool because they fail to express CD95.     

Intestinal lymphangiectasia, a disease characterized by selective loss of naive CD45RA+ lymphocytes into the gastrointestinal tract

Intestinal lymphangiectasia (InL) is a disease characterized by hypoproteinemia and lymphocytopenia resulting from blocked intestinal lymphatics and loss of lymph fluid into the gastrointestinal tract. This leads to immunologic abnormalities including hypogammaglobulinemia, skin anergy and impaired allograft rejection. In the present study, we evaluated whether the above immunologic abnormalities are secondary to a quantitative or qualitative disorder of T cells. In initial studies we demonstrated that adult InL patients' peripheral blood contain strikingly (and significantly) reduced numbers of CD4+/CD45RA+ T cells, whereas the numbers of CD4+/CD45RO+ T cells were only moderately (and not significantly) reduced. In addition, the CD4+/CD45RO+ T cell population contained an increased percentage of highly differentiated and previously sensitized cells, as demonstrated by decreased CD27 and CD31 expression and increased HLA-DR and CD69 expression. In subsequent functional studies, we showed that the InL CD4+/CD45RO+ T cells, when stimulated in vitro, proliferate fivefold less than control CD4+/CD45RO+ T cells and produce fourfold more IL-4 and threefold less IFN-gamma and IL-2. Thus, this cytokine production profile also reflects the highly differentiated nature of the residual cell population. Overall, these studies provide new information on the trafficking of naive/mature and Th1/Th2 T cell populations in this disease model.