TCR Alpha Beta Research Articles

Natural T cell immunity to intracellular pathogens and nonpeptidic immunoregulatory drugs.

Natural T (NT) lymphocytes recognize infected cells or microbial compounds without the classical genetic restriction of polymorphic major histocompatibility complex (MHC) molecules. This innate recognition pathway results in a broad and rapid antimicrobial response that may be critical for controlling the spread of intracellular pathogens, requiring the elimination of the infecting agent from both extracellular spaces and host cells. NT cells are mainly composed of alphabeta and gammadelta T lymphocytes that express natural killer (NK) receptors and recognize preferentially various nonpeptidic antigens. Similar to NK cells, NT lymphocytes can 'see' and kill target cells deficient in the expression of one or more MHC class I molecules. NT cells expressing the alphabeta TCR can recognize lipid and lipoglycan antigens presented in the context of nonpolymorphic CD1 molecules, whereas phosphocarbohydrates and akilamines induce constitutive responses in most Vgamma9Vdelta2 NT lymphocytes. The remaining fraction of gammadelta NT cells express the Vdelta1 chain associated with different Vgamma-chains and may directly recognize self-antigens such as MICA, MICB or CD1 molecules. It is possible that NT lymphocytes may play two opposite roles during intracellular infections. First, in the acute phase, they may be critical for the initiation of pathogen elimination. Second, in the chronic phase, NT cells may be dangerous, if their potential autoreactivity is not well controlled. It is conceivable that novel strategies of immune intervention against emerging and re-emerging intracellular pathogens, such as human immundeficiency virus (HIV), hepatitis-C virus (HCV) and Mycobacterium tuberculosis (MTB) may involve the control of NT cell activation/anergy by (nonpeptidic) immunoregulatory drugs.

P59fyn (Fyn) promotes the survival of anergic CD4-CD8- alpha beta TCR+ cells but negatively regulates their proliferative response to antigen stimulation.

T cell anergy is characterized by alterations in TCR signaling that may play a role in controlling the unresponsiveness of the anergic cell. We have addressed questions regarding the importance of the Src kinase p59(fyn) (Fyn) in this process by using Fyn null mice. We demonstrate that a mature population of CD4(-)CD8(-) alphabeta TCR(+) anergic T cells lacking Fyn have a substantial recovery of their proliferation defect in response to Ag stimulation. This recovery cannot be explained by ameliorated production of IL-2, and the improved proliferation correlates with an enhanced ability of the Fyn(-/-) anergic T cells to up-regulate the high affinity IL-2 receptor. We also observe that anergic CD4(-)CD8(-) alphabeta TCR(+) T cells have a heightened survival ability that is partially dependent on the elevated levels of Fyn and IL-2 receptor beta-chain expressed by these cells. The enhanced survival correlates with an increased capacity of the anergic cells to respond to IL-15. We conclude that Fyn plays an important role in aspects of T cell anergy pertaining to TCR signaling and to cell survival.

Immune potential of lymph node-derived lymphocytes in uncontrolled hemorrhagic shock.

The state of T cell immunity was evaluated in rats in early (1-4 h) hemorrhagic shock induced by a massive splenic injury. T cell subpopulations from treated and untreated shocked animals were tested by flow cytometry and the results were compared with healthy controls. A fall in CD4+ T lymphocyte and natural killer (NKR-P1+) cell number, marked decline in the T helper (CD4+) to T suppressor (CD8+) ratio, and decrease of interleukin-2 receptor (IL-2R) bearing cells in peripheral blood, mesenteric, and popliteal lymph nodes of rats was found in the early stages of hemorrhagic shock. The same phenotype profile was also revealed in lymphocytes of rats in hemorrhagic shock following massive splenic injury treated with Ringer's lactate. The number of TCRalpha beta and TCR-gamma delta positive cells, as well as the percentage of CD4 and CD8 positive cells in the thymus, was similar in all groups of rats. Culture of lymph node cells taken from rats following hemorrhage in the presence of 100 U/mL hrIL-2 resulted in a marked increase in the number of NKR-PI+ positive cells from 4.2% to 30.5% (P < 0.001). Magnet separated NKR-P1+ fractions lysed the allogeneic fibroblasts in the same manner as IL-2-activated NKR-P1 cells from the control rats. Popliteal lymph node (PLNi) CD8b+ lymphocytes from rats in hemorrhagic shock preinfected into the footpad with cytomegalovirus (CMV) 6 days prior to injury lost their ability to lyse the CMV-infected fibroblasts and protect the monolayer from CMV infection when compared with PLNi cells from control infected rats. The possible mechanisms for the observed cellular dysfunction following hemorrhage are discussed.

Major sites for the differentiation of V alpha 14(+) NKT cells inferred from the V-J junctional sequences of the invariant T-cell receptor alpha chain.

CD1d-restricted mouse NK1.1(+) TCR alpha beta(+) natural killer T (NKT) cells predominantly use an invariant TCR alpha chain encoded by V alpha 14 and J alpha 281 gene segments with a one-nucleotide N region. We found that NKT cells generated in the culture of fetal liver precursors possessed V alpha 14-J alpha 281 junctions that could be produced without the action of terminal deoxyribonucleotidyl transferase (TdT), indicating that NKT cells derived from fetal liver precursors are distinguishable from those from adult precursors with TdT expression. In fact, the frequency of the fetal-form sequences decreased with ageing. Surprisingly, the fetal-type sequences were predominantly observed in the lymphoid organs of athymic mice with the exception of bone marrow, where a sequence peculiar to the organ, with TdT-involved conversion from the invariant junction, was frequently present. These findings suggest that there are two independent sites of V alpha 14(+) NKT cell development, the hematopoietic organs throughout life (the developing liver and adult bone marrow) and, principally, the mature thymus.

Interleukin-2 signaling and the maintenance of self-tolerance.

IL-2 plays an important and complex role in the immune system, serving as a growth factor, a differentiation factor, and a regulator of cell death. It shares many of these functions with other cytokines such as IL-15, which complicates the interpretation of the IL-2-deficient phenotype. Nonetheless, it is clear that a major indispensable role of IL-2 signaling, at least in mice, is to limit the number of activated T cells in the periphery after exposure to self- or environmental antigens. Although we still do not understand the mechanism by which this occurs, there emerge several general conclusions that provide a foundation for future work on this issue. The autoimmune phenotype associated with IL-2 deficiency results from the dysregulated activity of thymus-derived TCR alpha beta CD4+ and/or CD8+ T cells. The process requires an initial antigenic stimulus (e.g., from intestinal flora or self-antigens), but can then spread to naive bystander T cells by an undefined mechanism. A key observation is that neighboring T cells with intact IL-2 signaling can suppress the dysregulated activity of IL-2- or IL-2R-deficient T cells in a dominant manner, indicating that IL-2-based immune regulation is a systemic rather than cell autonomous property. The IL-2R signal responsible for maintaining homeostasis is not dependent on either the Shc or Stat5 pathways, therefore AICD, which is Stat5-dependent in vitro, cannot be the critical mechanism. Finally, expression of the IL-2R in the thymus and not the periphery appears sufficient to suppress the autoimmune phenotype, suggesting that IL-2 signaling may be required for some aspect of thymocyte selection and/or differentiation that has so far gone undetected. These observations can be combined into a unified model wherein IL-2 signaling is required for the development of a regulatory T-cell subset that serves to terminate antigen-induced responses of TCR alpha beta T cells. On the other hand, the role of IL-2 in the maintenance of self-tolerance could be multifaceted, with no single model accounting for all experimental findings. Of note, most of our knowledge regarding IL-2 signaling and tolerance has come from studies of knockout mice. Conceptually, it is important to remember that the function of a molecule such as IL-2 is not simply the inverse of the phenotype seen when that molecule is absent, since necessity and sufficiency are not always coupled in physiological processes. In this regard, perhaps new insights into this important issue can be gained by better defining when and where IL-2 signaling normally occurs in wild-type animals and the functional status of the T cells involved.

Lymphokine-Dependent Proliferation of T-Lymphoid Cells: Regulated Responsiveness and Role In Vivo

The discovery of lymphokines stemmed from their ability to promote T-lymphocyte proliferation in vitro. Even after 20 years of intensive investigation, crucial aspects remain to be clarified about the role of specific lymphokines in T-cell proliferation and the biochemical mechanisms by which they play these roles, particularly in vivo. The present review focuses on conventional populations of TCR(alpha)beta T cells. Older findings and new insights into the function of specific lymphokines in T-lymphocyte proliferation in vivo are summarized along with unanswered questions raised by these observations. Vital contributions of lymphokines to clonal proliferation arise from two processes: the protection of cells against apoptosis and the activation of cell cycling. Findings are underscored indicating that the activity of a particular lymphokine depends on the subset of T cells (CD4 vs. CD8; naive vs. memory) to which it binds, and that point to potential pitfalls of extrapolating from tissue culture-adapted models to the regulation of T cells in vivo. After summaries of signaling mechanisms related to the proliferative activity of lymphokines, recent findings are highlighted suggesting that such signaling is a regulated and plastic process rather than one fixed schema of action.

Characterization of CD1d in mucosal immune function: an immunotherapeutic target for inflammatory bowel disease.

In addition to the classical MHC class I and class II molecules, human intestinal epithelial cells also express nonclassical MHC class I-like molecules on their cell surface. CD1d is a non-polymorphic MHC-like molecule whose expression is mainly localized to the epithelial cells of the gastrointestinal tract. The biochemical structure of CD1d on intestinal epithelial cells (IECs) exists in two forms: a 37-kD nonglycosylated, beta 2-microglobulin (beta 2M) independent and a 48-kD glycosylated, beta 2M dependent form. Immunolocalization studies suggest that the 37-kD nonglycosylated form of CD1d is limited to the apical cell surface whereas the 48-50-kD glycosylated, beta 2M dependent form of CD1d is expressed both on the apical and the basolateral surfaces. The beta 2M association with CD1d seems to be important in regulating the pattern of glycosylation and the localization of CD1d within the cell based upon studies of the structure of CD1d in a transfected model cell line and in polarized epithelial cell monolayers. The functional role of intestinal CD1d remains unknown. However, based upon in vitro studies of the antigens presented by human CD1d and mouse CD1d, CD1d expressed on IECs likely presents a very hydrophobic glycolipid molecule possibly from the cell wall of bacteria or host cells. The processed-lipid antigen presented by CD1d may then involve a yet-to-be-identified subpopulation of the resident, oligoclonal alpha beta TCR CD8+ intestinal intraepithelial lymphocyte (iIEL) T cells. Subsequently, these T cells would be very important in regulating the local immune response by producing cytokines and recruiting other immune modulating cells to destroy infected cells, regenerate normal IECs, and possibly downregulate activated T cells to maintain mucosal integrity.

Acute primary infection with cytomegalovirus (CMV) in kidney transplant recipients results in the appearance of a phenotypically aberrant CD8+ T cell population.

Human cytomegalovirus (CMV) is a beta-herpesvirus that causes a chronic subclinical infection in healthy man. The immune system is unable to eliminate the virus completely, allowing virus to persist in a latent state. In the immunocompromised host, this equilibrium is disturbed, resulting in a clinical infection. In immunocompromised rats, clinical CMV infection is associated with an increase in NK cells and CD8+ T cells, including a phenotypically aberrant CD8+ T cell population. Using flow cytometry, we examined the effect of acute CMV infection on the composition of leukocyte subsets in immunocompromised patients. Therefore, we used peripheral blood of CMV seronegative patients receiving a kidney from a seronegative (control group) or a seropositive donor. Of the patients receiving a seropositive kidney, only the patients undergoing acute CMV infection were included (experimental group). Special attention was paid to the phenotype of the cytotoxic T cells. The development of acute CMV infection resulted in an increased NK cell number and an activation of both CD4+ and CD8+ T cells, as determined by HLA-DR expression. An aberrant CD8+ T cell subset with decreased expression of CD8 and TCR alphabeta appeared in the infected patients. Furthermore, the size of this subpopulation of CD8+ T cells is positively correlated with the viral load.

Adhesion mediated by LFA-1 is required for efficient IL-12-induced NK and NKT cell cytotoxicity.

Interleukin 12 (IL-12)-activated NK1.1+TCRalpha beta+ (NKT2) and NK1.1+TCRalpha beta- (NK) cells exhibit cytotoxic activity against a wide variety of tumor cells in the absence of prior sensitization. Here we demonstrate that the integrin adhesion receptor LFA-1 (CD11a/CD18) regulates the cytotoxic activity of IL-12-activated NKT and NK cells against YAC-1 and EL-4 tumor cells. Differentiation in vivo and the expression of the cytolytic effector molecules perforin and Fas-L were comparable in both IL-12-activated NKT and NK cells from LFA-1-/ - and LFA-1+/+ mice. However, LFA-1-/-IL-12-activated NKT and NK cells showed impaired conjugate formation with target cells. These results provide the first genetic evidence for a role for an adhesion receptor in killing by IL-12-activated NK cells.

Early T cell development can be traced in rat fetal liver.

The degree of T cell commitment reached by cell precursors present in the fetal liver is a controversial issue. In the present work, the occurrence of fully T cell-committed progenitors among CD45+Thy-1+CD44+ 13-day-old rat fetal liver cells was demonstrated when limiting numbers of these cells in vitro reconstituted SCID mouse fetal thymic lobes providing single lineage-containing lobes for T, natural killer or dendritic cells. In addition, expression of rat pre-TCRalpha chain mRNA was detected in the CD45+ but not in the CD45- fetal liver cells and fully rearranged TCR VBeta8-Cbeta mRNA transcripts were specifically detected in the former population, demonstrating early transcription of some rearranged TCRVBeta genes in the rat fetal liver of 13 days of gestation. Finally, fetal liver organ cultures provided low numbers of TCR gamma delta T cells and CD2+CD8+NKR-P1A- intracytoplasmic CD3+ immature T cells, which intracellularly reacted with a mAb specific to the TCRalpha Beta molecule. These results prove T, NK and DC cell lineage determination at a prethymic stage in the fetal liver.

NF-kappa B is required for the positive selection of CD8+ thymocytes.

To examine the role of NF-kappaB in T cell development, we analyzed thymocyte ontogeny in transgenic (mutant I-kappaBalpha (mI-kappaBalpha)) mice that express a superinhibitory form of the NF-kappaB inhibitory protein, I-kappaBalpha (I-kappaBalpha(A32/36)), under the control of the T cell-specific CD2 promoter and enhancer. Thymi from mI-kappaBalpha mice contained increased numbers of double-positive (DP) and decreased numbers of both CD4(+) and CD8(+) single-positive cells, consistent with a block in DP thymocyte maturation. In addition, expression of CD69, a marker of positive selection, was decreased on DP thymocytes from the mI-kappaBalpha mice. To test directly whether NF-kappaB was required for positive or negative selection, we generated mI-kappaBalpha mice expressing the H-Y or 2C alphabeta TCR transgenes. Expression of the I-kappaBalpha(A32/36) transgene caused a block in the positive selection of CD8(+) single-positive cells in both strains of TCR transgenic animals. In contrast, negative selection was unaffected by expression of the I-kappaBalpha(A32/36) transgene. Taken together, these results identified a NF-kappaB-dependent transcriptional pathway that is selectively required for the positive selection of CD8(+) thymocytes.

Microenvironmental regulation of T cell development in the thymus

T cell development in the thymus occurs through a series of events beginning with thymic colonization by migrant precursors and ending with the emigration of functionally competent CD4+and CD8+T cells to the periphery. It is well accepted that signals through the pre-T cell receptor (pre-TCR) and alpha-beta TCR (αβ TCR) complex play pivotal roles in the maturation of CD4−8−and CD4+8+thymocytes, respectively. It is clear that stromal cells constituting the thymic microenvironment provide non-TCR-mediated interactions which are essential for several developmental events. Examples of such will be discussed here in relation to early and late events in T cell development.

Local challenge on oral mucosa with an alpha-gliadin related synthetic peptide in patients with celiac disease.

Gluten-derived peptides (e.g., amino-acids 31-49 of alpha-gliadin) have been shown to cause changes typical of celiac disease in the gut. Gluten-derived peptides have mostly been used in in vitro studies. The easiest access to the gastrointestinal system may be the mouth. In the present study we were interested to see whether a synthetic peptide corresponding to amino-acids 31-49 of alpha-gliadin could induce inflammatory changes in the oral mucosa after a local challenge in celiac disease patients. The challenge was made by injecting the peptide solution at a concentration of 10 microg/ml submucosally into the oral mucosa of 10 celiac disease patients after a gluten-free diet (GFD) and 12 healthy control subjects. B and CD45RO+ T cells, mast cells, CD3+, CD4+, CD8+ lymphocytes, and alphabeta and gammadelta T-cell receptor-bearing (TcR alphabeta, TcR gammadelta) lymphocytes were counted and HLA DR expression was determined. The expression of CD25 and Ki-67 antigen was also examined. The peptide significantly increased the total number of T cells in the lamina propria of the celiac disease patients. The expression of T-cell activation marker CD25 (IL-2 receptor), but not that of cell proliferation marker Ki-67, was also significantly increased in the lamina propria after peptide challenge. Such a reaction was not observed in the controls. The numbers of CD3+ and CD4+ T cells in the lamina propria were also increased in celiac disease patients after the challenge. The count of TcR gammadelta+ cells was very small in the oral mucosa in celiac disease and showed no increase when the oral mucosa was challenged with the peptide. The expression of HLA DR staining was enhanced after the submucosal peptide challenge in celiac disease; however, the difference was not statistically significant. The results show that in the celiac disease patients after the peptide challenge the oral mucosal lamina propria responds with a nonproliferative increase of lymphocytes. Thus, submucosal challenge with the peptide 31-49 can be used as an aid in the diagnosis of celiac disease. However, further studies with optimized methodology, including various concentrations of the peptide, adjuvants, other peptides, etc., are warranted, especially because the oral mucosa provides the easiest access to an in vivo peptide challenge in celiac disease.

Limited CD4 T-cell diversity associated with colitis in T-cell receptor α mutant mice requires a T helper 2 environment

T-cell receptor alpha mutant (TCRalpha(-/-)) mice spontaneously develop chronic colitis mediated by CD4(+) TCRalpha(-)beta(+) T cells. The aim of this study was to analyze the mechanisms of expansion of these cells by characterization of the TCRbeta repertoire. TCRbeta repertoire was analyzed by reverse-transcription polymerase chain reaction/Southern blot and DNA sequencing. Clonality of T cells was examined in the lymphoid tissues and colons of TCRalpha(-/-) mice and interleukin 4-deficient TCRalpha(-/-) mice. In addition, an in vitro culture system using syngeneic colonic epithelial cells as antigens was used. The clonal expansion of a restricted subset of Vbeta8.2(+) T cells was characterized by conservation of a single negatively charged amino acid residue in the second position of the complementarity-determining region 3 (CDR3). These T cells were observed in the diseased colon and appendix (cecal patch) of TCRalpha(-/-) mice, but not germfree TCRalpha(-/-) mice. Culture of polyclonal T cells from young TCRalpha(-/-) mice with colonic epithelial cells under T helper 2 conditions resulted in the survival of Vbeta8.2(+) T cells characterized by the same CDR3 pattern. In addition, the transfer of the cultivated T cells induced mild colitis in recombination-activating gene 1 mutant mice. In the TCRalpha(-/-) mice, the development of colitis is associated with the presence of a restricted diversity of Vbeta8. 2(+) T-cell subsets characterized by a specific TCR motif. The limited diversity of lamina propria T cells that are derived from naive T cells expanded by reacting with luminal bacterial antigens is likely caused by the survival of these T cells after stimulation with self-antigens in the presence of a T helper 2 environment.

Expression of Ly49A on T cells alters the threshold for T cell responses.

In this study we investigated the balance between activating and inhibitory signals during T cell activation. We have used transgenic mice in which CD8+ T cells expressed an inhibitory receptor, Ly49A, and a specific activating alphabeta TCR. This TCR recognizes an lymphocytic choriomeningitis virus peptide in combination with H-2Db. We observed a quantitative influence on cellular responses that depended upon the activating signals received through the TCR and the inhibitory signals received through Ly49A. By varying the peptide concentration given to stimulating cells or target cells, we could adjust the amount of ligand available to trigger the TCR. At low doses of peptide, Ly49A-expressing T cells were unresponsive on target cells that expressed H-2Dd, but responded against target cells without H-2Dd. However, this inhibition could be overcome by increasing the peptide concentration or by addition of anti-Ly49A F(ab')2 fragments. Thus, rather than behaving as simple "off" switches, our data indicate that Ly49 receptors modulate T cell signaling so that higher amounts of activating signals are required for effector-cell responses.

The epitope detected by cytotoxic T lymphocytes against thymus leukemia (TL) antigen is TAP independent.

Thymus leukemia (TL) antigens belong to the family of MHC class Ib antigens. We have shown in our previous studies that they serve as transplantation antigens, and can be recognized by both TCR alpha beta and TCR gamma delta cytotoxic T lymphocytes (CTL) with TL but not H-2 restriction. Although TL are known to be expressed TAP independently, it is unclear whether peptide loading on TL molecules is necessary for the formation of CTL epitopes. In the present study, we first showed that TL expression is beta(2)-microglobulin (beta(2)m)-dependent but TAP1 independent by flow cytometric analysis of thymocytes from beta(2)m- or TAP1-deficient mice crossed with TL transgenic mice expressing Tla(a)-3-TL on their thymocytes. Subsequently, we investigated the epitope recognized by CTL derived from C3H mice immunized with skin from a transgenic mouse expressing T3(b)-TL ubiquitously. Bulk CTL lines against TL from primary mixed lymphocyte cultures showed comparable cytotoxicity against T3(b)-TL transfectants of TAP2-deficient murine RMA-S grown at 37 degrees C to that against those grown at 25 degrees C. Furthermore, TCR alpha beta and TCR gamma delta CTL clones against TL recognized TL expressed on T3(b)-TL transfectants of RMA-S and Drosophila melanogaster cells having broad defects in peptide loading of MHC, and lysed these target cells. These results together indicate that TL-specific CTL populations primarily recognize epitopes expressed TAP independently.

A cytofluorimetric study of T lymphocyte subsets in rat lymphoid tissues (thymus, lymph nodes) and peripheral blood: a continuous remodelling during the first year of life

We previously demonstrated that the rat thymus undergoes a progressive remodelling long before the appearance of typical signs of involution [Quaglino, D., Capri, M., Bergamini, G., Euclidi, E., Zecca, L., Franceschi, C., Pasquali Ronchetti, I., 1998. Age-dependent remodelling of rat thymus. Morphological and cytofluorimetric analysis from birth up to one year of age. Eur. J. Cell. Biol. 76, 156-166]. To focus better on the complex remodelling that occurs in the rat immune system during the first year of life, we analysed the phenotype profile of thymocytes, and T lymphocytes from mesenteric lymph nodes and peripheral blood of the same animals by flow cytometry. Two experimental sets were performed simultaneously using the same animal strain, but starting and ending the study at different ages (15 days up to 300 days in the first experimental set, and 90 days up to 360 days of life in the second). In the rat these ages appear to be crucial not only for developmental, maturative and early involutional processes of the thymus, but also of the entire immune system. The main findings were the following: (1) in the thymus, CD8(-)CD4(-) cells increased, CD5(+)alphabeta TCR(-) and CD8(+)CD4(+) thymocytes decreased, while the most mature cell subset appeared well preserved with ageing; (2) in the lymph nodes, T helper and T cytotoxic lymphocytes decreased in the most aged animals. Memory/activated CD4(+)CD45RC(-) T cells decreased, while naive/resting CD4(+)CD45RC(+) cells increased in the youngest animals and decreased in the oldest. CD8(+)CD45RC(-) and CD8(+)CD45RC(+) lymphocytes showed a complex age-dependent trend, and (3) in peripheral blood, minor modifications were evident, such as an age-dependent increase in the alphabeta TCR(+)CD25(+) cell subset. Some of these changes were related to the developmental process, while others could likely be interpreted as early signs of immunosenescence. The role of these modifications in immune system is discussed within the framework of the remodelling hypothesis of immunosenescence. The age-dependent changes in these three lymphoid compartments, however, appear to be different and only partially overlapping, thus suggesting that the maturational, developmental and ageing processes have distinct characteristics in the central and peripheral lymphoid organs.

Requirement of residual thymus to restore normal T-cell subsets after human allogeneic bone marrow transplantation.

To determine the effect of residual thymic activity in reconstituting the T-cell system after T cell-depleting therapy, we monitored T-cell subsets of a unique thymectomized cancer patient in comparison to thymus-bearing patients after allogeneic bone marrow transplantation (BMT). T cells and T-cell subsets previously shown in murine studies to be regulated by the thymus were analyzed by FACS from 6 to >48 months after BMT. The investigation of thymus-bearing patients included 32 examinations of 9 children and 14 adults. None of the investigated cases had severe graft-versus-host disease or severe infections when examined. In the thymectomized host, T-cell regeneration occurred by donor cell expansion and was characterized by two prominent features: (i) a persistent failure to regenerate naive (CD45RA+) T-helper cells (14%, median), consistent with the recently developed concept of a thymus-dependency; and (ii) persistently elevated proportions of CD3+CD4-CD8- cells (double-negative cells, median 29%), which were identified in T cell receptor (TCR)gamma delta+ (22%, median of CD3+ cells, 88% double negatives) but also TCRalpha beta+ T-cell populations (78%, median of CD3+ cells, 17% double negatives). In thymus-bearing patients, 10 of 12 and 6 of 14 examinations of children and adults, respectively, performed later than 12 months after BMT showed the proportion of CD4+CD45RA+ cells appropriate for age (>52% and >28% in children and adults, respectively). Elevated double-negative cells (>10%) were found in only three patients, but none had elevated double-negative cells with a TCRalpha beta+ phenotype. Residual thymic activity might, in addition to its well-established role for regenerating naive T-helper (CD4+CD45RA+) cells, control the expansion of double-negative cells. A normal T-cell subset regeneration in a proportion of thymus-bearing adult hosts indicates the potential of an effective residual thymic activity even beyond childhood.

High frequency of circulating gamma delta T cells with dominance of the v(delta)1 subset in a healthy population.

TCR gamma delta(+) cells constitute <5% of all circulating T cells in healthy, adult Caucasians, and V(delta)1(+) cells constitute a minority of these cells. In contrast to TCR alpha beta(+) cells, their repertoire is selected extrathymically by environmental antigens. Although increased frequencies of V(delta)1(+) cells are found in several diseases, their function remains obscure. Here we show that the frequency of peripheral blood gamma delta T cells in healthy West Africans is about twice that of Caucasians, mainly due to a 5-fold increase in V(delta)1(+) cells, which is consequently the dominant subset. No age dependency of V(delta)1 frequencies was identified and the V(delta)1(+) cells in the African donors did not show preferential V(gamma) chain usage. Analysis of the CDR3 region size did not reveal any particular skewing of the V(delta)1 repertoire, although oligoclonality was more pronounced in adults compared to children. The proportions of CD8(+), CD38(+) and CD45RA(hi)CD45RO(-) cells within the V(delta)1(+) subset were higher in the African than in the European donors, without obvious differences in expression of activation markers. No significant correlations between levels of V(delta)1(+) cells and environmental antigens or immunological parameters were identified. Taken together, the evidence argues against a CDR3-restricted, antigen-driven expansion of V(delta)1(+) cells in the African study population. Our study shows that high frequencies of TCR gamma delta(+) cells with dominance of the V(delta)1(+) subset can occur at the population level in healthy people, raising questions about the physiological role of V(delta)1(+) T cells in the function and regulation of the immune system.

Regulatory role of mature B cells in a murine model of inflammatory bowel disease.

The spontaneous chronic colitis in TCR alpha mutant (TCRalpha(-/-)) mice mediated by CD4(+) TCRalpha(-)beta(+) T cells is more severe in the absence of mature B cells, suggesting a suppressive role of B cells and Ig in the development of chronic colitis. To investigate the direct role of B cells in the suppression of this colitis, cell transfer studies were performed in TCRalpha(-/-) x Igmu(-/-) (alphamu(-/-)) double-knockout mice. The chronic colitis was markedly attenuated in alphamu(-/-) mice after the adoptive transfer of peripheral B cells from TCRalpha(-/-) mice into 3- to 4-week-old alphamu(-/-) mice prior to the development of colitis. Furthermore, transfer of mature B cells from TCRalpha(-/-) mice markedly decreased the number of pathogenic colonic CD4(+) TCRalpha(-)beta(+) T cells in alphamu(-/-) mice with established colitis. This B cell effect required the presence of functional co-stimulatory molecules CD40 and B7-2 (CD86) but not B7-1 (CD80). These results indicate that mature B cells play an important role in the development of chronic colitis in TCRalpha(-/-) mice by directly regulating the pathogenic T cells (CD4(+) TCRalpha(-)beta(+) T cells).