Human T cell clones with gamma/delta and alpha/beta receptors are differently stimulated by monoclonal antibodies to CD2

Requirements for stimulating autocrine proliferation of human T cell clones expressing either alpha/beta or gamma/delta antigen receptors via the "alternative" CD2 pathway have been examined using a large set of monoclonal antibodies (mAb). In the presence of autologous accessory cells (AC, B-lymphoblastoid cell lines) 2 of 13 single CD2 mAb (CLB-T11.1/1 and 6F10.3) stimulated proliferation of gamma/delta but not alpha/beta cells. Interleukin (IL) 1 or IL 6 did not substitute for AC in stimulating gamma/delta clones. Addition of CD28 mAb YTH 913.12 with the CD2 mAb did not result in stimulation of any alpha/beta clones. In the absence of AC, none of the CD2 mAb singly could stimulate any T cell clones, but pairs of mAb directed to different epitopes of CD2 (CLB-T11.1/1 + CLB- T11.2/1 or 6F10.3 + 39C1.5) stimulated both alpha/beta and gamma/delta clones. In both cases, stimulation was reduced by the presence of CD3 mAb. These results confirm that the established AC-independent alternative pathway of T cell activation, which requires binding of two separate epitopes of CD2, operates in both gamma/delta and alpha/beta T cells, and further suggest that an additional pathway initiated by binding of a single CD2 epitope in the presence of AC is exclusively operational in gamma/delta cells.     

TCRαβ^＋CD^＋4CD^—8胸腺髓质细胞的表型分析

Phenotypic analysis of the medullary-type CD4+CD8- (CD4SP) thymocytes have revealed phenotypic heterogeneity within these cells. The phenotype of mature peripheral T cells is Qa-2+ HSA- CD69-, whereas in the medullary-type CD4SP thymocytes, the expression pattern of many markers were quite different, suggesting that the medullary-type CD4SP thymocytes may undergo phenotypic maturation. According to the results of two-color cytometry, seven discrete phenotypes were defined by the relative expression of Qa-2, HSA, CD69, 3G11 and 6C10: 3G11-6C10+CD69+HSAhi-->3G11+6C10+CD69+ HSAhi-->3G11+6C10-CD69+HSAint-->3G11+6C10- CD69-HSAint Qa-2(-)-->3G11+HSAlo/-Qa-2lo, at the same time, 3G11+6C10-CD69-HSAint Qa-2(-)-->3G11-HSAlo Qa-2(-)-->3G11-HSAlo/- Qa-2hi, the last two Qa-2 positive subsets could exit the thymus and home into periphery.     

Developmental potential of CD4-8- thymocytes. Peripheral progeny include mature CD4-8- T cells bearing alpha beta T cell receptor

We have used the intra-thymic transfer system to investigate the population dynamics of thymocyte and mature T cell subsets in the absence of continuing precursor input from the bone marrow. We have followed the development and life span of CD4+ and CD8+ thymocyte subsets and mature peripheral T cells from intra-thymically injected adult or fetal CD4-8- thymic precursors. Both precursor types proliferated, differentiated, and exported to peripheral lymphoid tissues alpha beta-TCR+CD4+8- and CD4-8+ progeny which formed a stable, long-lived component of the peripheral T cell pool. The production of phenotypically mature thymocytes and peripheral T cells occurred more rapidly from fetal CD4-8- precursors. CD4+8-:CD4-8+ ratios among peripheral progeny of intra-thymically-injected CD4-8- precursors were initially normal, but they steadily declined among progeny of the fetal precursors. Thus, there appear to be differences in the life span and/or proliferative capacity of mature T cells derived from embryonic vs adult progenitors. In addition to the predominant CD4+8- and CD4-8+ subsets of peripheral T cells, a minor (1 to 20%) population of Thy-1+CD3+4-8- T cells was identified among peripheral progeny of intra-thymically-injected CD4-8- thymocytes, as well as in lymph nodes of unmanipulated animals. A total of 20 to 34% of this subset expressed V beta 8+ TCR and the majority were CD5hi, Pgp-1+, and J11d-. The function and specificity of this newly identified population of thymically derived peripheral T cells remains to be investigated.     

Gads-/- mice reveal functionally distinct subsets of TCRbeta+ CD4-CD8- double-negative thymocytes

TCRbeta expression in CD4(-)CD8(-) double-negative (DN) thymocytes induces signaling pathways that promote survival and proliferation, as well as differentiation into CD4(+)CD8(+) double-positive thymocytes. The signaling pathways that regulate survival, proliferation, and differentiation remain unclear. We used Gads-deficient mice to investigate the signaling pathways that regulate these cell fates. During this investigation, we focused on TCRbeta(+) DN thymocytes and found that there are at least three functionally distinct subsets of TCRbeta(+) DN thymocytes: TCRbeta(+) DN3E, TCRbeta(+) DN3L, and TCRbeta(+) DN4. Survival and proliferation of TCRbeta(+) DN3E were independent of Gads, but survival and proliferation of TCRbeta(+) DN3L cells were Gads dependent. Likewise, expression of Bcl-2 in TCRbeta(+) DN3E cells was Gads independent, but Gads was necessary for Bcl-2 expression in TCRbeta(+) DN3L cells. Bcl-2 expression was not dependent on Gads in TCRbeta(+) DN4 cells, but proliferation of TCRbeta(+) DN4 cells was Gads dependent. Gads was not required for the differentiation of DN thymocytes into DP thymocytes. In fact, Gads(-/-) DN3E cells differentiated into DP thymocytes more readily than wild-type cells. We conclude that signaling pathways required to initiate TCRbeta-induced survival and proliferation are distinct from the pathways that maintain survival and proliferation. Furthermore, signaling pathways that promote survival and proliferation may slow differentiation.     

CD2 expression correlates with proliferative capacity of alpha beta + or gamma delta + CD4-CD8- T cells in lpr mice.

The T lymphocytes that accumulate in vast numbers in the lymphoid tissues of lpr/lpr (lpr) mice express a TCR-alpha beta that is polyclonally rearranged, and yet is devoid of surface CD4 or CD8 (CD4-8-) as well as CD2. lpr CD2- alpha beta + CD4-8- T cells exhibit an apparent block in signal transduction, in that when activated they produce little or no IL-2 and proliferate minimally in the absence of exogenous IL-2. In contrast to the predominant hyporesponsive alpha beta + CD4-8- T cells, we observe that a minor subset (1 to 2%) of lpr lymph node CD4-8- cells expresses a TCR-gamma delta and can proliferate upon activation with PMA and ionomycin in the absence of exogenous IL-2. Furthermore, these responsive gamma delta T cells express surface CD2. The functional and phenotypic distinctions of lpr gamma delta T cells led us to identify an analogous minor (4 to 10%) subset of alpha beta + CD4-8- cells in lpr thymus and lymph nodes that does express CD2. Similar to the gamma delta subset, these CD2+ alpha beta + CD4-8- cells are also capable of proliferation and IL-2 production. Thus the capacity for IL-2 production and proliferation by a small proportion of lpr CD4-8- T cells, either alpha beta + or gamma delta +, correlates with their expression of surface CD2. This correlation is supported by the observation that the lpr liver contains actively cycling alpha beta + CD4-8- lymphocytes that are strikingly enriched for CD2 expression. Consequently, unlike the vast proportion of abnormal lpr CD2- CD3+ CD4-8- cells, the CD2+ CD3+ CD4-8- T cells may not express the basic lpr defect, or else are not affected by its presence. These studies suggest that expression of the lpr abnormality may be restricted to a particular T cell lineage. This functional correlation with CD2 expression may be more broadly applicable to phenotypically similar subsets of normal thymocytes, and possibly peripheral tolerized T lymphocytes.     

CD8+ alpha/beta or gamma/delta T cell receptor-bearing T cells from athymic nude mice are cytolytically active in vivo.

Phenotypic analysis of lymphocytes that mature extrathymically in congenitally athymic nude mice has revealed a large population of CD3+ CD8+ T cells that express gamma/delta-TCR. In euthymic mice, significant numbers of cells with this phenotype are found only in the intestinal epithelium. Intestinal intraepithelial lymphocytes have been shown to be cytolytically active in vivo, as measured by the redirected lysis assay. In this communication, freshly harvested T cell subsets obtained from pooled nude mouse spleen and lymph nodes and separated by flow cytometric cell sorting were assayed for their ability to lyse FcR+ P815 targets in the presence of mAb to the epsilon-chain of the CD3 complex. CD8+, but not CD4+ or CD4- CD8-, T cells in nude mice were cytolytically active. CD8+ alpha/beta- and gamma/delta-TCR-bearing T cells from the spleen and lymph nodes of nude mice demonstrated similar cytolytic activity. No cytolytic activity of purified cell subsets was apparent in the absence of anti-CD3 mAb, even when NK-susceptible target cells were used. These data indicate that, in contrast to euthymic mice, a large proportion of CD8+ cells from the spleen and lymph nodes of nude mice are cytolytically active in vivo. In addition, these results suggest that the intestinal epithelium is not the only anatomical location where constitutively cytolytic CD8+ alpha/beta- or gamma/delta TCR-bearing T cells may be found.     

Peripheral murine CD3+, CD4-, CD8- T lymphocytes express novel T cell receptor gamma delta structures

A mAb directed against the CD3 molecule was used to identify a subset of CD3+, CD4-, CD8- T cells previously undefined in the peripheral lymphoid organs of the mouse. Biochemical analysis of CD3+, CD4-, CD8- splenocytes revealed that the vast majority of these cells express one of at least two distinct CD3-associated TCR gamma delta heterodimeric structures, but no detectable TCR alpha beta. One disulfide-linked heterodimer (77 kDa) is composed of two chains of 45 to 46 and 32 kDa. The latter chain was immunoprecipitated with an anti-TCR C gamma 1/C gamma 2 antiserum and was not glycosylated. An antiserum produced against a peptide corresponding to the C-terminal region of the predicted C gamma 4 gene product immunoprecipitated additional heterodimers (80 to 90 kDa). One heterodimer, composed of disulfide-linked 41- to 45-kDa protein (including a V gamma/C gamma 4 component), is expressed on a T cell hybridoma, DN-1.21, which was derived from fused splenic CD3+, CD4-, CD8- T cells. Another V gamma/C gamma 4-containing heterodimer is composed of disulfide-linked 46- to 47-kDa glycoproteins. These findings demonstrate that CD3+, CD4-, CD8- T cells present in the peripheral lymphoid organs express a variety of paired TCR gamma delta proteins. Unlike CD3+, CD4-, CD8- thymocytes, these cells express high levels of C gamma 4, but little, if any TCR alpha beta.     

Agonist-dependent single channel current and gating in alpha4beta2delta and alpha1beta2gamma2S GABAA receptors

The family of gamma-aminobutyric acid type A receptors (GABA(A)Rs) mediates two types of inhibition in the mammalian brain. Phasic inhibition is mediated by synaptic GABA(A)Rs that are mainly comprised of alpha(1), beta(2), and gamma(2) subunits, whereas tonic inhibition is mediated by extrasynaptic GABA(A)Rs comprised of alpha(4/6), beta(2), and delta subunits. We investigated the activation properties of recombinant alpha(4)beta(2)delta and alpha(1)beta(2)gamma(2S) GABA(A)Rs in response to GABA and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3(2H)-one (THIP) using electrophysiological recordings from outside-out membrane patches. Rapid agonist application experiments indicated that THIP produced faster opening rates at alpha(4)beta(2)delta GABA(A)Rs (beta approximately 1600 s(-1)) than at alpha(1)beta(2)gamma(2S) GABA(A)Rs (beta approximately 460 s(-1)), whereas GABA activated alpha(1)beta(2)gamma(2S) GABA(A)Rs more rapidly (beta approximately 1800 s(-1)) than alpha(4)beta(2)delta GABA(A)Rs (beta < 440 s(-1)). Single channel recordings of alpha(1)beta(2)gamma(2S) and alpha(4)beta(2)delta GABA(A)Rs showed that both channels open to a main conductance state of approximately 25 pS at -70 mV when activated by GABA and low concentrations of THIP, whereas saturating concentrations of THIP elicited approximately 36 pS openings at both channels. Saturating concentrations of GABA elicited brief (<10 ms) openings with low intraburst open probability (P(O) approximately 0.3) at alpha(4)beta(2)delta GABA(A)Rs and at least two "modes" of single channel bursting activity, lasting approximately 100 ms at alpha(1)beta(2)gamma(2S) GABA(A)Rs. The most prevalent bursting mode had a P(O) of approximately 0.7 and was described by a reaction scheme with three open and three shut states, whereas the "high" P(O) mode ( approximately 0.9) was characterized by two shut and three open states. Single channel activity elicited by THIP in alpha(4)beta(2)delta and alpha(1)beta(2)gamma(2S) GABA(A)Rs occurred as a single population of bursts (P(O) approximately 0.4-0.5) of moderate duration (approximately 33 ms) that could be described by schemes containing two shut and two open states for both GABA(A)Rs. Our data identify kinetic properties that are receptor-subtype specific and others that are agonist specific, including unitary conductance.     

The majority of CD4+8- thymocytes are functionally immature.

The thymus is the major site of T cell development and repertoire selection. During these processes, T cells segregate into two subsets that express either CD4 or CD8 accessory molecules, the phenotype of peripheral T cells. Analysis of CD4+8- thymocytes revealed that the majority of these cells express the heat-stable Ag (HSA) but not the nonclassical class I Ag, Qa-2. This HSA+, Qa-2- phenotype is similar to that of the less mature, CD4+8+ thymocytes. The remaining CD4+8- thymocytes possess the HSA-, Qa-2+ phenotype of peripheral T cells. To determine whether the Qa-2-, CD4+8- thymic subset is fully mature, we have analyzed the functional status of these CD4+8- subpopulations. The results indicate that only those thymocytes which express Qa-2 are fully responsive to anti-TCR stimulation in a manner analogous to peripheral T cells. The Qa-2- subset is nonresponsive to stimulation by anti-TCR antibodies that have been immobilized to plastic, even in the presence of lymphokines or syngeneic APC. This subset is, however, capable of proliferating to allogeneic cells or to anti-TCR on the surface of syngeneic APC, although not to the levels achieved by Qa-2+ thymocytes. Thus, the Qa-2- subset appears to require additional interactions which are not necessary for peripheral T cells or Qa-2+ thymocytes. Relevant to this issue, the Qa-2+ thymocyte subset does not appear until relatively late in development, and does not reach adult frequencies until several weeks after birth. These results would suggest that there is a progression from HSA+, Qa-2- to HSA-, Qa-2+ which parallels the maturation of functional responsiveness. These findings are important to understanding T cell selection since thymocytes with such a decreased responsiveness may have a differential capacity for tolerance induction. The results presented suggest that the bulk of CD4+8- thymocytes are not fully mature and that Qa-2 may serve as a marker for T cells with a more complete functional competence.     

CD3 delta deficiency arrests development of the alpha beta but not the gamma delta T cell lineage.

The CD3 complex found associated with the T cell receptor (TCR) is essential for signal transduction following TCR engagement. During T cell development, TCR-mediated signalling promotes the transition from one developmental stage to the next and controls whether a thymocyte undergoes positive or negative selection. The roles of particular CD3 components in these events remain unclear. Indeed, it is unknown whether they have specialized or overlapping roles. However, the multiplicity of CD3 components and their evolutionary conservation suggest that they serve distinct functions. Here the developmental requirement for the CD3 delta chain is analyzed by generating a mouse line specifically lacking this component (delta-/- mice). Strikingly, CD3 delta is shown to be differentially required during development. In particular, CD3 delta is not needed for steps in development mediated by pre-TCR or gamma delta TCR, but is required for further development of thymocytes expressing alpha beta TCR. Absence of CD3 delta specifically blocks the thymic selection processes that mediate the transition from the double-positive to single-positive stages of development.     

Functional status of interleukin 2 receptors expressed by immature (Lyt-2-/L3T4-) thymocytes

A subpopulation of phenotypically immature (Lyt-2-/L3T4-) thymocytes express receptors for the polypeptide hormone interleukin 2 (IL 2); however, these cells do not proliferate in vitro in response to IL 2. In investigating this phenomenon in greater detail, we observed that the IL 2 receptors (IL 2-R) on freshly isolated immature thymocytes bound IL 2 with about fivefold lower affinity (Kd approximately 100 pM) than IL 2-R on activated mature T cells and T cell lines (Kd approximately 20 pM). Furthermore, in contrast to activated T cells, Lyt-2-/L3T4- thymocytes did not endocytose bound IL 2. When stimulated in short-term culture with a combination of phorbol ester (PMA) and calcium ionophore, Lyt-2-/L3T4- thymocytes proliferated in a largely IL 2-dependent fashion. IL 2-R expression on these activated cells initially disappeared (at 24 hr) and subsequently reappeared (at 48 to 72 hr). Reexpressed IL 2-R on activated thymocytes resembled those on mature T lymphocytes in that they bound IL 2 with high affinity (Kd = 15 to 25 pM) and were capable of endocytosing IL 2. Taken together, these data place certain constraints on the putative physiologic role of IL 2 in intrathymic growth regulation.     

Intestinal CD8 alpha alpha and CD8 alpha beta intraepithelial lymphocytes are thymus derived and exhibit subtle differences in TCR beta repertoires

Intraepithelial lymphocytes (IEL) of the small intestine are anatomically positioned to be in the first line of cellular defense against enteric pathogens. Therefore, determining the origin of these cells has important implications for the mechanisms of T cell maturation and repertoire selection. Recent evidence suggests that murine CD8 alpha alpha intestinal IELs (iIELs) can mature and undergo selection in the absence of a thymus. We analyzed IEL origin by cell transfer, using two congenic chicken strains. Embryonic day 14 and adult thymocytes did not contain any detectable CD8 alpha alpha T cells. However, when TCR(+) thymocytes were injected into congenic animals, they migrated to the gut and developed into CD8alphaalpha iIELs, while TCR(-) T cell progenitors did not. The TCR V beta 1 repertoire of CD8 alpha alpha(+) TCR V beta 1(+) iIELs contained only part of the TCR V beta 1 repertoire of total iIELs, and it exhibited no new members compared with CD8(+) T cells in the thymus. This indicated that these T cells emigrated from the thymus at an early stage in their developmental process. In conclusion, we show that while CD8 alpha alpha iIELs originate in the thymus, T cells acquire the expression of CD8 alpha alpha homodimers in the gut microenvironment.     

Molecular characterization of the WC1 antigen expressed specifically on bovine CD4-CD8- gamma delta T lymphocytes.

Although gamma delta T lymphocytes were identified several years ago, the functional importance of these cells remains to be established. gamma delta T cells of ruminants are unique in two respects. First, they are present at much higher levels compared to man and rodents. Second, ruminant CD4-CD8- gamma delta T cells uniquely express a 220 kD surface Ag recognized by a panel of mAb, recently clustered as WC1. WC1 has been most extensively studied in sheep with the use of the mAb T19. Here, we report on the isolation of a full length cDNA clone, encoding the WC1 Ag, from a COS cell cDNA expression library prepared from a bovine gamma delta T cell line. The protein encoded by the pWC1 cDNA clone was reactive with the bovine mAb CC15 and IL.A29, and with T19. The cDNA clone consisted of 4475 bp and contained a single long open reading frame of 1436 amino acids. The pWC1 cDNA clone encoded a type 1 integral membrane protein with an extracellular domain consisting of 11 scavenger receptor cysteine-rich-repeats with homology to CD5 and CD6. Southern blotting suggested that the bovine genome contained multiple sequences highly related to the isolated WC1 cDNA. Furthermore, WC1-like sequences were present in the genomes of all mammals tested including mouse and man. The molecular characterization of the WC1 Ag as reported here provides a starting point for the definition of its role in gamma delta T cell biology.     

NK1.1+ thymocytes. Adult murine CD4-, CD8- thymocytes contain an NK1.1+, CD3+, CD5hi, CD44hi, TCR-V beta 8+ subset.

CD4-, CD8- thymocytes were purified from thymi obtained from normal C57BL/6 mice. By flow cytometry analysis, 5 to 10% of these double negative (DN) thymocytes were found to express NK1.1 on their surface. The NK1.1+ DN thymocytes were demonstrated, by two-color fluorescence, to be CD3lo, CD5hi, CD44hi, J11d-, B220-, MEL 14-, IL2R- with 60% expressing TCR-V beta 8 as determined by the mAb F23.1. In contrast, splenic and peripheral blood NK cells were NK1.1+, CD3-, CD5-, TCR-V beta 8- with 40 to 60% being MEL 14+. Unlike peripheral NK cells, fresh DN thymocytes enriched for NK1.1+ cells were unable to kill YAC-1, the classical murine NK cell target. However, these cells were able to mediate anti-CD3 redirected lysis even when they were assayed immediately after purification, i.e., with no culture or stimulation. These data demonstrate that adult murine thymocytes contain NK1.1+ cells which are distinct, both by function and phenotype, from peripheral NK cells. These data also raise the issue of a possible NK/T bipotential progenitor cell.     

A murine thymic stromal cell line which may support the differentiation of CD4-8- thymocytes into CD4+8- alpha beta T cell receptor positive T cells.

A fibroblastoid cell line TSt-4 was established from fetal thymus tissue of C57BL/6 mice. When fetal thymus (FT) cells or CD4-8- (DN) cells of adult thymuses were cultured on the monolayer of TSt-4, a considerable proportion of lymphocytes expressed CD4 or both CD4 and CD8 within 1 day, and the CD4+CD8- cells were maintained further while the CD4+8+ cells disappeared by Day 5. A large proportion of cells generated from DN cells but not FT cells was shown to express CD3 and T cell receptor alpha beta. Addition of recombinant interleukin (IL)-7 into the cultures resulted in a marked increase of cell recovery without virtual change in differentiation process of alpha beta lineage. The present work strongly suggests that thymic fibroblasts play an important role in T cell differentiation and IL-7 contributes to supporting proliferation of differentiated cells.     

Mice lacking alpha/beta and gamma interferon receptors are susceptible to junin virus infection

Junin virus (JUNV) causes a highly lethal human disease, Argentine hemorrhagic fever. Previous work has demonstrated the requirement for human transferrin receptor 1 for virus entry, and the absence of the receptor was proposed to be a major cause for the resistance of laboratory mice to JUNV infection. In this study, we present for the first time in vivo evidence that the disruption of interferon signaling is sufficient to generate a disease-susceptible mouse model for JUNV infection. After peripheral inoculation with virulent JUNV, adult mice lacking alpha/beta and gamma interferon receptors developed disseminated infection and severe disease.     

Human CD8 beta, but not mouse CD8 beta, can be expressed in the absence of CD8 alpha as a beta beta homodimer

The T cell coreceptor CD8 exists on mature T cells as disulfide-linked homodimers of CD8 alpha polypeptide chains and heterodimers of CD8 alpha- and CD8 beta-chains. The function of the CD8 alpha-chain for binding to MHC class I and associating with the tyrosine kinase p56lck was demonstrated with CD8 alpha alpha homodimers. CD8 alpha beta functions as a better coreceptor, but the actual function of CD8 beta is less clear. Addressing this issue has been hampered by the apparent inability of CD8 beta to be expressed without CD8 alpha. This study demonstrates that human, but not mouse, CD8 beta can be expressed on the cell surface without CD8 alpha in both transfected COS-7 cells and murine lymphocytes. By creating chimeric proteins, we show that the murine Ig domain of CD8 beta is responsible for the lack of expression of murine CD8 beta beta dimers. In contrast to CD8 alpha alpha, CD8 beta beta is unable to bind MHC class I in a cell-cell adhesion assay. Detection of this form of CD8 should facilitate studies on the function of the CD8 beta-chain and indicates that caution should be used when interpreting studies on CD8 function using chimeric protein with the murine CD8 beta beta Ig domain. In addition, we demonstrate that the Ig domains of CD8 alpha are also involved in controlling the ability of CD8 to be expressed. Mutation of B- and F-strand cysteine residues in CD8 alpha reduced the ability of the protein to fold properly and, therefore, to be expressed.