Interleukin 2 deficiency is a common feature of autoimmune mice

IL 2 production was studied in autoimmune mice to assess the role of this lymphokine in the pathogenesis of murine lupus. Spleen and lymph node cells from autoimmune-susceptible mice show an age-dependent loss in the ability to produce functional IL 2. This defect correlates with disease expression and is most severe in MLR/Mp-Ipr/Ipr mice. MLR/Mp-Ipr/Ipr thymocytes gradually lose responsiveness to IL 2 with age. These results suggest that the immunoregulatory abnormalities of autoimmune mice may be due in part to IL 2 deficiency.     

CD8+ T lymphocytes in double alpha beta TCR transgenic mice. II. Competitive fitness of dual alpha beta TCR CD8+ T lymphocytes in the peripheral pools.

We studied Rag2-deficient mice bearing two rearranged alphabeta TCR transgenes, both restricted to the MHC H-2D(b) class I molecule. We have previously shown that, in these DTg mice, most peripheral CD8 T cells express one TCRbeta chain associated with two TCRalpha chains, as in one-third of the mature T cells from normal mice. We examined the functional behavior of the dual-receptor CD8 T cells developing either in the absence or in the presence of self-Ag. The dual-receptor CD8 T cells, which develop in absence of self-Ag, show efficient responses to immunization and remain sensitive to induction of peripheral tolerance. In contrast to single TCR T cells, the dual-TCR cells, when tolerized upon exposure to high levels of self-Ag, are not deleted and therefore may exert important regulatory functions. When developing in the presence of self-Ag, the dual-receptor-expressing CD8 T cells escape central deletion, but are not fully competent to respond to cognate stimuli. Overall, we found that the dual-TCR CD8 T cells show a poor competitive value and can be out-competed by single-TCR cells, both in the course of immune responses and in reconstitution experiments. The decreased fitness of the dual-receptor cells may contribute to diminishing the autoimmune hazard that they could represent.     

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.     

Clonal deletion and autoreactivity in extrathymic CD4-CD8-(double negative) T cell receptor-alpha/beta T cells.

Peripheral CD4-CD8- (double negative) T cells (DNT cells) that express TCR-alpha/beta (DNT-alpha/beta cells) are expanded in some autoimmunity-prone mice, but in normal mice these cells have not been extensively studied. In this study, we isolated splenic DNT-alpha/beta cells that are Thy-1+, Ly-1+, MAC-1-, J11d-, and Ia-. Only 5% of these cells were B220+. Freshly isolated DNT-alpha/beta cells did not proliferate in MLC; however, these cells responded strongly to stimulation with matrix-bound anti-TCR-alpha/beta antibodies or Con A. After activation the cells became CD4+CD8-, acquired high reactivity in both syngeneic and allogeneic MLC, but lacked cytotoxicity. After activation the cells gradually reverted to a double-negative phenotype in culture. Surprisingly, despite high autoreactivity the analysis of TCR V beta expression revealed a near normal pattern of Mls-1a- and I-E-induced clonal deletions. These findings reveal that DNT-alpha/beta cells are subject to negative selection and that autoreactivity cannot be attributed to a general failure of clonal deletion in this T cell subpopulation. DNT-alpha/beta cells may normally remain tolerant by down-regulating the CD4 molecule.     

Tyrosine phosphorylation of a c-Src-like protein is increased in membranes of CD4- CD8- T lymphocytes from lpr/lpr mice.

Mice homozygous for the autosomal recessive lpr gene have a disorder that results in autoimmunity and massive accumulation of T lymphocytes lacking CD4 and CD8 surface markers. These abnormal T cells exhibit constitutive tyrosine phosphorylation of a component of the CD3-T-cell receptor complex. We compared membrane tyrosine phosphorylation in lpr/lpr CD4- CD8- T cells and control T cells, lpr membranes exhibited a 7.3-fold increase (n = 16) in tyrosine phosphorylation of a 60-kilodalton protein. The increase was correlated with the Lpr but not the CD4- CD8- phenotype in that p60 phosphorylation was not increased in membranes from normal CD4- CD8- thymocytes. To identify the p60 in lpr cells, we examined the activity of several T-cell tyrosine-specific protein kinases. p56lck phosphorylation was only slightly increased in lpr membranes (2.2-fold; n = 16). Phorbol ester treatment of intact T cells before membrane isolation caused p56lck to migrate as pp60lck; however, pp60lck could be clearly distinguished from the pp60 in lpr cells by two-dimensional gel electrophoresis. The pp60 from lpr cells exhibited several isoforms at pH approximately 6.3 to 6.5. Although on two-dimensional gels pp60c-src had a pI (6.4 to 6.8) within a similar region, p60c-src mRNA, protein, and kinase activities were not increased in lpr cells. In addition, staphylococcal V8 proteolytic cleavage of the lpr pp60 isolated on two-dimensional gels yielded two major fragments, a pattern distinct from that of pp60c-src. However, by using an antiserum against the C-terminal sequence of c-Src and other related kinases, including p59fyn, the pp60 could be immunoprecipitated in greater amounts from lpr than from control T cells. When pp59(fyn) was selectively immunoprecipitated from T-cell membranes with specific antisera, its molecular weight, proteolytic cleavage pattern, and behavior on two-dimensional gels were identical to those of the pp60 from lpr cells. We conclude that p59(fyn) phosphorylation is increased in membranes from lpr/lpr CD4(-) CD8(-) T cells and that the increase is correlated with constitutive tyrosine phosphorylation and perhaps with the expansion of this unusual T-cell population.     

Studies of CD4- CD8- alpha beta bone marrow T cells with suppressor activity.

The predominant T cell subset in the bone marrow of specific pathogen-free C57BL/Ka and BALB/c mice expressed the alpha beta+ TCR CD4- CD8- surface phenotype. Purified C57BL/Ka alpha beta+ TCR CD4- CD8- marrow cells obtained by cell sorting suppressed the MLR of C57BL/Ka responder and BALB/c stimulator spleen cells. Although the percentage of typical T cells in the spleen was markedly reduced in adult nude mice or normal neonatal mice as compared to the normal adult, the percentage of alpha beta+ TCR CD4- CD8- cells in the spleen and marrow was not. The percentage of "self-reactive" V beta 5+ T cells in the BALB/c spleen was markedly reduced as compared to that in the C57BL/Ka spleen. However, the percentages in the bone marrow were similar. The results indicate that the predominant subset of marrow T cells in these pathogen-free mice differ with regard to surface marker phenotype, function, dependence on the adult thymus, and deletion of certain self-reactive V beta receptors as compared to typical spleen T cells. The marrow T cells appear to develop directly from marrow precursors without rearranged beta chain genes during a 48 hour in vitro culture.     

Interleukin 4 induces CD4+/CD8- to CD8+/CD4- transformation of human neonatal T cells by way of a double positive intermediate

We have determined that IL-4 induces the generation of CD4+/CD8+ T cells in cultures of neonatal lymphocytes. Sorting, positive, and negative selection experiments indicate that these cells arise from a subpopulation of CD4+/CD8- cells present in the neonate but not in the adult. We have further determined that these IL-4 generated "double positive" cells further differentiate to express only the CD8 marker. Our findings suggest an undescribed and dramatic role for IL-4 in T cell differentiation.     

Signaling lymphocyte activation molecule-associated protein is a negative regulator of the CD8 T cell response in mice

The primary manifestation of X-linked lymphoproliferative syndrome, caused by a dysfunctional adapter protein, signaling lymphocyte activation molecule-associated protein (SAP), is an excessive T cell response upon EBV infection. Using the SAP-/- mouse as a model system for the human disease, we compared the response of CD8+ T cells from wild-type (wt) and mutant mice to various stimuli. First, we observed that CD8+ T cells from SAP-/- mice proliferate more vigorously than those from wt mice upon CD3/CD28 cross-linking in vitro. Second, we analyzed the consequence of SAP deficiency on CTL effector function and homeostasis. For this purpose, SAP-/- and wt mice were infected with the murine gamma-herpesvirus 68 (MHV-68). At 2 wk postinfection, the level of viral-specific CTL was much higher in mutant than in wt mice, measured both ex vivo and in vivo. In addition, we established that throughout 45 days of MHV-68 infection the frequency of virus-specific CD8+ T cells producing IFN-gamma was significantly higher in SAP-/- mice. Consequently, the level of latent infection by MHV-68 was considerably lower in SAP-/- mice, which indicates that SAP-/- CTL control this infection more efficiently than wt CTL. Finally, we found that the Vbeta4-specific CD8+ T cell expansion triggered by MHV-68 infection is also enhanced and prolonged in SAP-/- mice. Taken together, our data indicate that SAP functions as a negative regulator of CD8+ T cell activation.     

Defective clonogenic potential of CD8+ T lymphocytes in patients with AIDS. Expansion in vivo of a nonclonogenic CD3+CD8+DR+CD25- T cell population

This study examines the potential mechanism(s) responsible for the defective clonability of CD8+ T lymphocytes in patients with AIDS. By the combined use of one- and two-color fluorescence cytofluorometry we have shown an increase in the number of circulating DR+ cells due to the expression of DR on a relatively large proportion of T lymphocytes (one-third of CD3+ cells), the majority of them belonging to the CD8+ subset. In addition, the majority of CD8+DR+ cells in AIDS patients did not express CD25 Ag (the receptor for IL-2), a surface marker generally expressed on normal activated T lymphocytes. Sorted CD8+DR+ and CD8+DR- cell populations were analyzed comparatively for their ability to proliferate in response to different stimuli, including anti-CD3, anti-CD2, alone or in combination with anti-CD28 mAb and mitogens such as PHA, alone or in combination with PMA. We have demonstrated that CD8+DR+ cells were severely defective in their proliferative response to triggering via these major pathways of T cell activation even when an exogenous source of IL-2 or IL-4 was added to the microcultures 24 h after initiating the cultures. In contrast, CD8+DR- cells showed a significant proliferation in response to the different stimuli and the proliferative response was strongly enhanced by the addition of IL-2 or IL-4. At the end of the stimulation period CD8+DR+ and CD8+DR- proliferating populations were analyzed for CD25 Ag expression. Only 1 to 10% of CD8+DR+ cells expressed CD25 antigen compared with 40 to 50% of CD8+DR- cells. The proliferative defect of CD8+DR+ cells was further confirmed in experiments performed at the clonal level. The analysis of the frequency of proliferating T lymphocyte-precursors in both CD8+DR+ and CD8+DR- subsets showed that the defective clonogenic potential of CD8+ cells in AIDS patients could be in large part ascribed to CD8+DR+ cells. Five percent of CD8+DR+ cells showed a clonogenic potential compared to the 25% of CD8+DR- cells. Finally, we analyzed the surface expression of VLA-2 Ag, a marker of a chronic state of T cell activation, on circulating T lymphocytes. We have shown that a large proportion of CD3+DR+CD25- cells (50 to 80% in the different patients with AIDS analyzed) expressed VLA-2 Ag.(ABSTRACT TRUNCATED AT 400 WORDS)     

Functional characterization of MHC class II-restricted CD8+CD4- and CD8-CD4- T cell responses to infection in CD4-/- mice

Classical CD4(+) and CD8(+) T cells recognize Ag presented by MHC class II (MHCII) and MHC class I (MHCI), respectively. However, our results show that CD4(-/-) mice mount a strong, readily detectable CD8(+) T cell response to MHCII-restricted epitopes after a primary bacterial or viral infection. These MHCII-restricted CD8(+)CD4(-) T cells are more similar to classical CD8(+) T cells than to CD4(+) T cells in their expression of effector functions during a primary infection, yet they also differ from MHCI-restricted CD8(+) T cells by their inability to produce high levels of the cytolytic molecule granzyme B. After resolution of a primary infection, epitope-specific MHCII-restricted T cells in CD4(-/-) mice persist for a long period of time as memory T cells. Surprisingly, upon reinfection the secondary MHCII-restricted response in CD4(-/-) mice consists mainly of CD8(-)CD4(-) T cells. In contrast to CD8(+) T cells, MHCII-restricted CD8(-)CD4(-) T cells are capable of producing IL-2 in addition to IFN-gamma and thus appear to have attributes characteristic of CD4(+) T cells rather than CD8(+) T cells. Therefore, MHCII-restricted T cells in CD4(-/-) mice do not share all phenotypic and functional characteristics with MHCI-restricted CD8(+) T cells or with MHCII-restricted CD4(+) T cells, but, rather, adopt attributes from each of these subsets. These results have implications for understanding thymic T cell selection and for elucidating the mechanisms regulating the peripheral immune response and memory differentiation.     

Human CD4- CD8- alpha beta+ T cells express a functional T cell receptor and can be activated by superantigens.

The CD4 and CD8 molecules play an important role in the stimulation of T cells and in the process of thymic education. Most mature T cells express the alpha beta TCR and either CD4 or CD8; however, there is a small population of alpha beta+ TCR T cells that lack both CD4 and CD8. Little is known of the biology of the CD4- CD8- (double-negative) alpha beta+ TCR T cells or the nature of the Ag to which they may respond. These cells not only represent a novel population of T cells but also provide useful biologic tools to study the roles that CD4 and CD8 play in T cell activation. In this study we have addressed two questions. Firstly, whether CD4- CD8- alpha beta+ TCR T cells have functionally active TCR and, secondly, whether CD4 or CD8 is required for the activation of T cells by bacterial enterotoxins. Six double-negative alpha beta+ TCR T cell clones, propagated from two healthy donors, were challenged with a panel of nine bacterial enterotoxins. The V alpha and V beta usage of their TCR was determined by polymerase chain reaction. All of the CD4-CD8- clones proliferated in response to at least one of the enterotoxins, in a V beta-specific manner. The proliferative response of the CD4-CD8- alpha beta+ TCR T cell clones was similar in magnitude to that exhibited by CD4+ T cell clones of known V beta expression. These data clearly show that the CD4 and CD8 molecules are not required for the activation of untransformed human T cells by bacterial enterotoxins. Furthermore, these results indicate that CD4-CD8- alpha beta+ TCR T cells, normally present in all individuals, are not functionally silent, because they can be stimulated via their TCR. Their physiologic role, like that of gamma delta T cells, remains to be elucidated.     

Identification of a novel human thymocyte subset with a phenotype of CD3- CD4+ CD8 alpha + beta-1. Possible progeny of the CD3- CD4- CD8- subset.

We investigated responsiveness to cytokines and differentiating potential of early human T cell precursors in vitro. Human CD3- CD4- CD8- (triple negative) thymocytes were highly purified by using magnetic bead columns and cell sorting. These cells proliferated for the first 3 to 4 days and then remained viable for up to 14 days in the presence of IL-7, IL-2 or IL-4 had only limited growth-promoting activity on these cells and could not maintain the cell viability. We followed the phenotypic change of triple negative thymocytes during culture with IL-7. After 7 to 14 days of culture with IL-7, a considerable proportion became CD4+ CD8+ (double positive). These cells were found to be CD3- CD4+ CD8 alpha+ beta- in contrast to common double positive thymocytes, which express low levels of CD3 and both alpha- and beta-chains of CD8. By using four-color immunofluorescence and multi-parameter cytofluorometric analysis, we could identify this novel subset in fresh thymocytes. These results suggest that the CD3- CD4+ CD8 alpha+ beta- subset exists physiologically in the human thymus and may represent an intermediate stage between triple negative and common double positive thymocytes.     

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.     

Anti-TCR antibody treatment activates a novel population of nonintestinal CD8 alpha alpha+ TCR alpha beta+ regulatory T cells and prevents experimental autoimmune encephalomyelitis

CD8alphaalpha+CD4-TCRalphabeta+ T cells are a special lineage of T cells found predominantly within the intestine as intraepithelial lymphocytes and have been shown to be involved in the maintenance of immune homeostasis. Although these cells are independent of classical MHC class I (class Ia) molecules, their origin and function in peripheral lymphoid tissues are unknown. We have recently identified a novel subset of nonintestinal CD8alphaalpha+CD4-TCRalphabeta+ regulatory T cells (CD8alphaalpha Tregs) that recognize a TCR peptide from the conserved CDR2 region of the TCR Vbeta8.2-chain in the context of a class Ib molecule, Qa-1a, and control- activated Vbeta8.2+ T cells mediating experimental autoimmune encephalomyelitis. Using flow cytometry, spectratyping, and real-time PCR analysis of T cell clones and short-term lines, we have determined the TCR repertoire of the CD8alphaalpha regulatory T cells (Tregs) and found that they predominantly use the TCR Vbeta6 gene segment. In vivo injection of anti-TCR Vbeta6 mAb results in activation of the CD8alphaalpha Tregs, inhibition of the Th1-like pathogenic response to the immunizing Ag, and protection from experimental autoimmune encephalomyelitis. These data suggest that activation of the CD8alphaalpha Tregs present in peripheral lymphoid organs other than the gut can be exploited for the control of T cell-mediated autoimmune diseases.     

Functional similarity and differences between selection-independent CD4-CD8- alphabeta T cells and positively selected CD8 T cells expressing the same TCR and the induction of anergy in CD4-CD8- alphabeta T cells in antigen-expressing mice.

In TCR-alphabeta transgenic mice, CD4-CD8- TCR-alphabeta+ (alphabeta DN) cells arise in the absence of positively selecting MHC molecules and are resistant to clonal deletion in Ag-expressing mice. In this study the activation requirements and functional properties of alphabeta double-negative (DN) cells were compared with those of positively selected CD8+ cells expressing equivalent levels of the same MHC class I-restricted transgenic TCR. We found that positively selected CD8+ cells required a lower density of the antigenic ligand for optimal proliferative responses compared with alphabeta DN cells derived from nonpositively selecting mice. However, when the CD8 coreceptor on CD8+ cells was blocked with an anti-CD8 mAb, both alphabeta DN and CD8+ cells exhibited the same dose-response curve to the antigenic ligand and the same dependence on CD28/B7 costimulation. Positively selected CD8+ cells also differed from alphabeta DN cells in that they differentiated into more efficient killers and IL-2 producers after Ag stimulation, even after CD8 blockade. However, Ag-activated alphabeta DN and CD8+ cells were equally efficient in producing IFN-gamma, suggesting that this functional property is independent of positive selection. We also found that alphabeta DN cells recovered from the lymph nodes of Ag-expressing mice were functionally anergic. This anergic state was associated with defective proliferation and IL-2 production in response to Ag stimulation. These observations indicate that alphabeta DN cells can be anergized in vivo by physiological levels of the antigenic ligand.     

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.     

Defective signal transduction in CD4-CD8- T cells of lpr mice

Mice homozygous for the lpr gene develop a lymphoproliferative disorder due to expansion of a subset of CD4-CD8- T cells. Triggering of the T-cell receptor in these lpr T cells does not lead to translocation of protein kinase C or phosphorylation of CD3, interleukin-2 production, or proliferation, whereas a combination of phorbol ester and calcium ionophore does. Stimulation with concanavalin A or anti-CD3 induces phosphoinositide hydrolysis. The rise in inositol bisphosphate, inositol triphosphate, and inositol tetrakisphosphate, identified by HPLC, is similar in +/+ and lpr T cells. The concentration of cytoplasmic free calcium ([Ca2+]i), however, under basal and stimulated conditions is significantly lower in lpr T cells. The lower basal [Ca2+]i may explain why induction of proliferation with phorbol ester and calcium ionophore requires a higher concentration of ionophore in these cells than in normal T cells. The lower [Ca2+]i obtained on stimulation may contribute to the activation defect of CD4-CD8- lpr T cells.     

T cell-induced Ig allotypic suppression in mice. II. Both CD4+ CD8- and CD4- CD8+ T cell subsets from sensitized Igha mice are required to induce suppression of Igh-1b allotype expression

We established the phenotype of T splenocytes (Ts) from Igha/a BALB/c mice sensitized against B splenocytes from the Ighb/b CB20 congenic mice that induce Igh-1b (IgG2a of the Ighb haplotype) suppression. This was achieved by studying the action of anti-T cell subset mAb on the capacity of Ts to induce this chronic allotypic suppression in Igha/b (BALB/c x CB20)F1 mice. The Ts were treated with cytotoxic anti-mouse CD4 or anti-mouse CD8 rat mAb in vitro before their injection into the Igha/b newborns or in vivo after their injection into the Igha/b newborns. Exposure to either anti-CD8 or anti-CD4 mAb in vitro or in vivo leads to loss of the capacity of Ts to induce Igh-1b allotypic suppression. Mixing CD4+-cell-depleted Ts and CD8+-cell-depleted Ts preparations restored the capacity of the cells to induce Igh-1b suppression. Thus, both CD4+ CD8- Ts and CD4- CD8+ Ts are required for the induction of this allotypic suppression. Bone marrow cells and B splenocytes from Igh-1b-suppressed adult Igha/b mice were shown to be able to durably express Igh-1b when transferred into irradiated Igha/a BALB/c hosts whereas whole spleen cells from such donors failed to do it. Abrogation of Igh-1b suppression by in vivo anti-CD8 mAb treatment was achieved in adult Igha/b heterozygotes but with a lower efficiency than in adult Ighb/b homozygotes, all being chronically Igh-1b suppressed. The CD4- CD8+ cell population essential for maintaining this suppression is resistant to in vivo 600 rad irradiation and seems to be slightly inhibited by in vivo administration of free Igh-1b.     

A viral long terminal repeat expressed in CD4+CD8+ precursors is downregulated in mature peripheral CD4-CD8+ or CD4+CD8- T cells.

The long terminal repeat from a thymotropic mouse mammary tumor virus variant, DMBA-LV, was used to drive the expression of two reporter genes, murine c-myc and human CD4, in transgenic mice. Expression was observed specifically in thymic immature cells. Expression of c-myc in these cells induced oligoclonal CD4+ CD8+ T-cell thymomas. Expression of human CD4 was restricted to thymic progenitor CD4- CD8- and CD4+ CD8+ T cells and was shut off in mature CD4+ CD8- and CD4- CD8+ T cells, known to be derived from the progenitor double-positive T cells. These results suggest the existence of similar and common factors in CD4+ CD8- and CD4- CD8+ T cells and support a model of differentiation of CD4+ CD8+ T cells through common signal(s) involved in turning off the expression of the CD4 or CD8 gene.