Characterization of the murine antigenic determinant, designated L3T4a, recognized by monoclonal antibody GK1.5: expression of L3T4a by functional T cell clones appears to correlate primarily with class II MHC antigen-reactivity

MRL/lpr CD4- CD8- and CD8+ T cells, respectively, mediate Fas-dependent and perforin cytotoxic pathways

Autoimmune-prone MRL/lpr mice, homozygous for the lpr mutation, exhibit defective apoptosis and develop generalized lymphoproliferation with the accumulation of a double-negative (DN: CD4- CD8-) T cell population. The capacity of lpr T lymphocytes to effectuate Fas- and perforin-mediated cytotoxicity was investigated. Spleen and lymph nodes cells spontaneously lyse Fas- targets (thymocytes) through a Fas-mediated mechanism as a consequence of their overexpression of Fas ligand (FasL) confirmed by semiquantitative reverse transcription (RT)-PCR and immunoprecipitation analysis. This cytotoxicity was greatly increased after stimulation of the effectors by phorbol myristate acetate (PMA) + ionomycin. Under these conditions, MRL/lpr spleen and LN cells exhibited strong Fas-mediated Ca2+-independent cytotoxic activity against wild-type Fas+ (H-2 compatible or incompatible) thymocytes or lipopolysaccharide (LPS)-transformed blast cells. Such Fas-mediated cytotoxic activity was also observed with C57BL/6-lpr, but never with wild-type C57BL/6 or MLR+/+ effectors. Depletion experiments showed that the effector cells of this Fas-mediated cytotoxicity were DN T cells. This subset, which represent in vivo activated T cells, can spontaneously lyse Fas+ targets by a mechanism that does not need the interaction of the T cell receptor (TCR) with major histocompatibility complex molecule plus antigen. This lytic potential is increased by PMA + ionomycin, which sends a second activation signal to these primed T cells. Therefore, the small amounts of Fas receptor expressed on MRL/lpr tissues may account for their nonspecific autoimmune attack by DN cells. In Con A-containing medium, which allows detection of the perforin-mediated pathway against Fas targets, cytotoxic CD8+ effectors were detected that are able to kill lpr thymocytes via a Ca2+-dependent pathway. Thus, in MRL/lpr mice, these CD8+ cells could constitute potent cytotoxic effectors against cells presenting antigen to their TCR.

Role of bcl-2 in the Development of Lymphoid Cells From the Hematopoietic Stem Cell

To investigate the role of bcl-2 in lymphohematopoiesis, a long-term bone marrow reconstitution system was established. Transplantation of 1,000 c-Kit+ Sca-1+ and lineage markers negative cells from bcl-2−/− mouse bone marrow resulted in long-term reconstitution of nonlymphoid cells. However, T cells were totally absent and B-lymphocyte development was severely impaired at a very early stage of differentiation in the chimeric mouse. On the other hand, transplantation of day 14 fetal liver cells from bcl-2−/− mice resulted in generation of both T and B cells in the recipient, albeit transiently. These data suggest that bcl-2 plays a critical role in the development of lymphoid progenitor cells from the hematopoietic stem cell (HSC), but is not essential for the development of nonlymphoid cells and the self-renewal of HSC. In addition, lymphopoiesis from fetal liver HSC appears to be less dependent on bcl-2 than adult bone marrow HSC.

CD8 T cells from major histocompatibility complex class II-deficient mice respond vigorously to class II molecules in a primary mixed lymphocyte reaction

Mature CD4+ and CD8+ T cells are restricted by major histocompatibility complex (MHC) class II and class I molecules, respectively. In a primary mixed lymphocyte reaction (MLR), CD8+ T cells from C57BL/6 (B6) mice can respond to allo-class I molecules, but not allo-class II molecules. However, a significant fraction of CD8+ T cells from C57BL/6 class II-deficient (B6Aalpha-) mice violate this rule by responding vigorously in a MLR to class II molecules. The frequency of responding cells is approximately 50% of that of B6 CD8+ T cells responding to B6bm1 allo-class I molecules. This response requires neither appropriate co-receptor, i.e. CD4, nor exogenous lymphokines, indicating that interactions between the T cell receptors (TCR) and class II molecules are remarkably efficient. Since these CD8+ T cells are positively selected by class I molecules in the thymus of class II-deficient mice, these CD8+ T cells should interact with both classes of MHC molecules. The absence of thymic negative selection by class II molecules may result in the production of these CD8+ T cells. The data imply that a substantial fraction of CD4+CD8+ double-positive thymocytes in wild-type mice interacts with both classes of MHC molecules prior to thymic selection.

Interactions Between c-kit and Stem Cell Factor Are Not Required for B-Cell Development In Vivo

The receptor-type tyrosine kinase, c-kit is expressed in hematopoietic stem cells (HSC), myeloid, and lymphoid precursors. In c-kit ligand-deficient mice, absolute numbers of HSC are mildly reduced suggesting that c-kit is not essential for HSC development. However, c-kit− HSC cannot form spleen colonies or reconstitute hematopoietic functions in lethally irradiated recipient mice. Based on in in vitro experiments, a critical role of c-kit in B-cell development was suggested. Here we have investigated the B-cell development of c-kitnull mutant (W/W ) mice in vivo. Furthermore, day 13 fetal liver cells from wild type or W/W mice were transferred into immunodeficient RAG-2−/− mice. Surprisingly, transferred c-kit− cells gave rise to all stages of immature B cells in the bone marrow and subsequently to mature conventional B2, as well as B1, type B cells in the recipients to the same extent as transferred wild type cells. Hence, in contrast to important roles of c-kit in the expansion of HSC and the generation of erythroid and myeloid lineages and T-cell precursors, c-kit− HSC can colonize the recipient bone marrow and differentiate into B cells in the absence of c-kit.

Developmental regulation of VDJ recombination by the core fragment of the T cell receptor alpha enhancer

The role of T cell receptor alpha enhancer (E alpha) cis-acting elements in the developmental regulation of VDJ recombination at the TCR alpha/delta locus was examined in transgenic mice containing variants of a minilocus VDJ recombination substrate. We demonstrate that the 116-bp T alpha 1,2 core enhancer fragment of the 1.4-kb E alpha is sufficient to activate the enhancer-dependent step of minilocus rearrangement, and that within T alpha 1,2, intact binding sites for TCF/LEF and Ets family transcription factors are essential. Although minilocus rearrangement under the control of the 1.4-kb E alpha initiates at fetal day 16.5 and is strictly limited to alpha beta T cells, we find that rearrangement under the control of T alpha 1,2 initiates slightly earlier during ontogeny and occurs in both gamma delta and alpha beta T cells. We conclude that the core fragment of E alpha can establish accessibility to the recombinase in developing thymocytes in vivo in a fashion that is dependent on the binding of TCF/LEF and Ets family transcription factors, but that these and other factors that bind to the E alpha core cannot account for the precise developmental onset of accessibility that is provided by the intact E alpha. Rather, our data suggests a critical role for factors that bind E alpha outside of the core T alpha 1,2 region in establishing the precise developmental onset of TCR alpha rearrangement in vivo.

Co-receptor-independent signal transduction in a mismatched CD8+ major histocompatibility complex class II-specific allogeneic cytotoxic T lymphocyte

The contribution of co-receptors in signal transduction upon T cell receptor (TCR)-mediated recognition of major histocompatibility complex (MHC) class II antigen by mature T lymphocytes expressing TCR derived from the apparently co-receptor-independent, I-Ak-specific allogeneic CD8+ CTL clone QM11 has been examined. Mature double-negative, CD8+ and CD4+ bulk T cell lines and clones expressing TCR(QM11) were developed from TCR(QM11) transgenic mice. All these T cells, irrespective of co-receptor expression, showed specific lytic activity on cells expressing I-Ak. Furthermore, co-receptorless mutants were obtained from a CD4+ and CD8+ clone. The responses of these co-receptorless mutants upon specific recognition of the alloantigen, as judged by cytolytic activity, granule exocytosis, lymphokine production, proliferation, and tyrosine phosphorylation of the zeta chain, were comparable to those of the original clones. Thus, the results proved the co-receptor independence of the recognition of I-Ak by TCR(QM11) and further indicated there is no indispensable unique signal transduced by co-receptors. However, when the amount of the available antigen was limited by anti-I-Ak antibody, the CD4+ T cell clone showed a remarkable resistance to the inhibition whereas the mismatched CD8+ clone was readily inhibitable. The anti-I-Ak-resistant component of the CD4+ clone showed dependency on the CD4 molecule. Taken collectively, the results indicate that the role played by a co-receptor molecule in mature T cells is purely quantitative amplification of the signal through the formation of a TCR/MHC/co-receptor ternary complex, and also indicate that the role of co-receptor molecules as TCR-independent adhesion molecules is at best minimal.

Blockade of CD28/B7 co-stimulation by mCTLA4-Hgamma1 inhibits antigen-induced lung eosinophilia but not Th2 cell development or recruitment in the lung

We have studied the role of the CD28/B7 co-stimulatory pathway in the development of a Th2-type lung immune response. Mice injected two or three times intraperitoneally with ovalbumin in alum adjuvant and then re-exposed to the same antigen by intranasal (i.n.) inoculation show infiltration of the lung tissue and appearance in the broncho-alveolar lavage (BAL) fluid of significant numbers of eosinophils and lymphocytes, in a pattern which is reminiscent of asthmatic inflammation. The accumulation of eosinophils in the airways is completely dependent on interleukin (IL)-5 secretion by CD4+ T cells. We have used mice transgenic for a soluble form of murine CTLA-4 (mCTLA4-Hgamma1) which binds to B7 molecules on antigen-presenting cells, thereby preventing their interaction with T cell-expressed CD28. mCTLA4-Hgamma1-transgenic mice immunized intraperitoneally and challenged i.n. with ovalbumin failed to generate any eosinophil infiltration, suggesting that little or no IL-5 was secreted in the lungs of these mice. In contrast with the complete lack of eosinophils, the numbers and phenotypes of infiltrating lymphocytes were comparable in the lungs of mCTLA4-Hgamma1-transgenic and normal mice. Also, lung lymphocytes from immunized mCTLA4-Hgamma1-transgenic and normal mice could be shown to secrete comparable amounts of IL-4 and IL-5 when stimulated in culture in the absence of mCTLA4-Hgamma1. We conclude that mCTLA4-Hgamma1 can efficiently block the production of IL-5 during in vivo responses and inhibit eosinophil recruitment, but that it does not block the development of CD4+ T cells into Th2 cells with the potential to secrete IL-5.

Loss of the beta 1 subunit of the sodium pump during lymphocyte differentiation

The Na,K-ATPase, or sodium pump, is responsible for maintaining cellular volume and is involved in receptor-mediated endocytosis; it is a ubiquitous transmembrane enzyme in higher eukaryotes and consists of an alpha and a beta subunit. In the mouse, two isotypes of beta with no known function have been identified: beta 1 and beta 2. We have studied the expression of beta 1 and beta 2 in lymphocytes from bone marrow, spleen, peripheral blood, and thymus. The beta 2 subunit is not expressed in any of the lymphocytes tested. Pre-B lymphocytes and the majority of mature, resting B cells in the bone marrow express the beta 1 subunit, as do all pre-T cells and mature thymocytes. In the spleen and in blood, beta 1 expression defines subsets of T and B lymphocytes. Mitogen-stimulated T and B cells lose beta 1 expression and do not express beta 2. While there is no indication that there is a change in alpha subunit isoform expression as a result of lymphocyte activation or that it is expressed in smaller amounts, there is a switch in the expression of the beta isoform.

Role of CD8+ lymphocytes in host defense against Pneumocystis carinii in mice

An improved understanding of host defense against Pneumocystis carinii could provide novel therapeutic modalities directed against this opportunistic pathogen. Immunodeficient mouse models confirm the role of CD4+ lymphocytes in defense against P. carinii, but the role of CD8+ lymphocytes is controversial. BALB/c mice specifically depleted of CD4+ lymphocytes are susceptible to P. carinii, recruiting large numbers of CD8+ lymphocytes to their lungs during infection. Because of this recruitment, we hypothesized that CD8+ lymphocytes could participate in host defense against P. carinii. BALB/c mice were depleted of CD4+ lymphocytes, CD8+ lymphocytes, or both CD4+ and CD8+ lymphocytes. All mice were then inoculated intratracheally with P. carinii. Mice depleted of CD4+ lymphocytes became moderately infected with P. carinii. Mice depleted of CD8+ lymphocytes cleared the inoculum, indicating that CD8+ lymphocytes are unnecessary for defense when CD4+ lymphocytes are available. However, mice depleted of both CD4+ and CD8+ lymphocytes became significantly more intensely infected than mice depleted of CD4+ lymphocytes alone. Therefore, CD8+ lymphocytes participate in defense against P. carinii in vivo during depletion of CD4+ lymphocytes. To determine the mechanisms of this protection, CD8+ lymphocytes were purified from the lungs of CD4-depleted mice during infection. Lung CD8+ lymphocytes proliferated in response to P. carinii antigen and elaborated interferon-gamma in vitro. Thus CD8+ lymphocytes provide defense against P. carinii in vivo, and the elaboration of interferon-gamma likely represents one important mechanism of defense. During states of CD4+ lymphocyte depletion, the modulation of CD8+ lymphocyte function may provide alternative approaches to the host defense against opportunistic pathogens.

CD4+ but not CD8+ cells are essential for allorejection

The generation of knockout mice with targeted gene disruption has provided a valuable tool for studying the immune response. Here we describe the use of CD4 and CD8 knockout mice to examine the role of CD4+ and CD8+ cells in initiating allotransplantation rejection. Pretreatment with a brief course of depletive anti-CD4 monoclonal antibody therapy allowed permanent survival of heart, but not skin, allografts transplanted across a major histocompatibility barrier. However, skin as well as heart grafts were permanently accepted in the CD4 knockout mice. Transfer of CD4+ cells into CD4 knockout recipient mice 1 d before skin engraftment reconstituted rejection, demonstrating that CD4+ cells are necessary for initiating rejection of allogeneic transplants. Major histocompatibility complex disparate heart and skin allografts transplanted into CD8 knockout recipients were rejected within 10 d. This study demonstrates that CD4+ but not CD8+ T cells are absolutely required to initiate allograft rejection.

A developmental switch in lymphocyte homing receptor and endothelial vascular addressin expression regulates lymphocyte homing and permits CD4+ CD3- cells to colonize lymph nodes

IN adult mice, the dominant adhesion molecules involved in homing to lymph nodes are L-selectin homing receptors on lymphocytes and the peripheral lymph node addressins on specialized high endothelial venules. Here we show that, from fetal life through the first 24 hr of life, the dominant adhesion molecules are the mucosal addressin MAdCAM-1 on lymph node high endothelial venules and its counterreceptor, the Peyer's patch homing receptor, integrin alpha 4 beta 7 on circulating cells. Before birth, 40-70% of peripheral blood leukocytes are L-selectin-positive, while only 1-2% expresses alpha 4 beta 7. However, the fetal lymph nodes preferentially attract alpha 4 beta 7-expressing cells, and this can be blocked by fetal administration of anti-MAdCAM-1 antibodies. During fetal and early neonatal life, when only MAdCAM-1 is expressed on high endothelial venules, an unusual subset of CD4 + CD3- cells, exclusively expressing alpha 4 beta 7 as homing receptors, enters the lymph nodes. Beginning 24 hr after birth a developmental switch occurs, and the peripheral node addressins are upregulated on high endothelial venules in peripheral and mesenteric lymph nodes. This switch in addressin expression facilitates tissue-selective lymphocyte migration and mediates a sequential entry of different cell populations into the lymph nodes.

MHC class II molecules are not required for survival of newly generated CD4+ T cells, but affect their long-term life span

We grafted fetal thymi from wild-type mice into immunodeficient RAG-2-/- or class II-/-RAG-2-/- (class II MHC-) recipients and followed the fate of naive CD4+ T cells derived from the grafts. In both types of recipients, newly generated CD4+ T cells proliferated to the same extent in the periphery and rapidly filled the empty T cell compartment. However, CD4+ T cells in class II- recipients gradually decreased in number over 6 months. These results show that interactions between the TCR and class II molecules are not required for newly generated CD4+ T cells to survive and proliferate, but are necessary to maintain the size of the peripheral T cell pool for extended periods.

Induction of sensitivity to activation-induced death in primary CD4+ cells: a role for interleukin-2 in the negative regulation of responses by mature CD4+ T cells

We examine the requirements for converting naive, mature CD4+ cells from an activation-induced death (AID)-resistant to a -sensitive phenotype. Priming for sensitivity to AID can be divided into two steps. The first is a mitogen/CD3-dependent, cyclosporin-sensitive signal and the second a cytokine-dependent, cyclosporin-insensitive one. Under these conditions, interleukin (IL)-2, but not IL-4, IL-7 or IL-15, the receptors of which share a common receptor gamma chain, is capable of providing the cytokine signal for inducing sensitivity to AID. Increased expression of the low-affinity IL-2R alpha chain (CD25) is associated with acquisition of AID sensitivity and antibodies to CD25 block acquisition of AID sensitivity in the presence of IL-2. As with T cell hybridomas, AID is dependent on both CD95 and CD95 ligand (CD95L) expression, but unlike hybridomas, the sensitive and resistant phenotypes of primary CD4+ cells cannot be distinguished by levels of CD95 expression, functional CD95L nor the fraction of cells in cycle. The results suggest that the unique function of IL-2 is to regulate proteins, either not important or constitutively regulated in T cell hybridomas, that are essential for cell-autonomous suicide of activated CD4+ cells. These experiments provide a mechanism for the recent observations of chronic lymphoproliferation and autoimmune disease in mice with null mutations in IL-2 or CD25.

Altered T cell receptor ligands trigger a subset of early T cell signals

TCR ligands are complexes of peptides and MHC proteins on the surfaces of APCs. Some of these ligands cause T cell proliferation (agonists), while others block it (antagonists). We compared the acid release, calcium flux, and proliferation response of helper T cells to a variety of ligands. We found that all agonist ligands but not most antagonist ligands trigger acid release, a general indicator of early cellular activation. Only a subset of ligands triggering acid release cause sustained calcium flux, and only a subset of these ligands cause T cell proliferation. Antagonist ligands and anti-CD4 antibodies both effectively block T cell proliferation. However, significantly greater antagonist ligand or antibody concentrations are required to block acid release and initial calcium influx. These data demonstrate a hierarchy of early T cell signaling steps and show that altered TCR ligands can initiate some steps while blocking the completion of others.

CD4+ cytolytic effectors are inefficient in the clearance of Listeria monocytogenes

Cytotoxic T lymphocytes (CTL) recognize and lyse target cells through the interaction of the T-cell receptor complex with the class I or class II major histocompatibility complex (MHC). The production of class I-restricted CTL has been shown to be critical to the elimination of specific pathogens including Listeria monocytogenes. However, the function of class II-restricted CTL in the clearance of intracellular pathogens is poorly understood. H-2b beta 2-microglobulin-deficient mice (beta 2M-/-) are not able to produce CD8+ CTL in response to infection with L. monocytogenes. We used this model to evaluate the efficacy of class II-restricted CTL, in the absence of a class I-restricted response, during a primary infection with L. monocytogenes. We demonstrate that, despite their effectiveness in adoptive transfer of protection, Listeria-specific CD4+ class II-restricted cytotoxic lymphocytes are ineffective in decreasing titres of L. monocytogenes in the spleen was found established infection. In beta 2M-/- mice, persistence of L. monocytogenes in the spleen was found preferentially in class II-negative cells. Surprisingly, class I-restricted CTL from C57BL/6 mice were capable of decreasing bacterial titres during an established infection even in the absence of detectable class I on the surface of cells from beta 2M-/- mice. These data strongly suggest that, in the absence of a class I-restricted response, pathogens that elicit a class II-restricted cytotoxic response may escape prompt eradication by the immune system.

T lymphocyte development in the absence of Fc epsilon receptor I gamma subunit: analysis of thymic-dependent and independent alpha beta and gamma delta pathways

During fetal development, early thymocyte progenitors transiently express low affinity Fc receptors for IgG (Fc gamma R) of both Fc gamma RII and III isoforms. Only the Fc gamma RIII isoform requires association of an Fc gamma RIII (CD16) alpha subunit with an Fc epsilon RI gamma homodimer for surface expression. To address the role of Fc gamma R in ontogeny, we studied thymic development in Fc epsilon RI gamma-/- mice. We fine that day 14.5 CD4-CD8- double-negative (DN) fetal thymocytes of Fc epsilon RI gamma-/- mice express mRNA of both Fc gamma RIIb1 and Fc gamma RIII. Surface expression of Fc gamma RII/III is readily detected on these cells. It appears that Fc gamma RIIb1, whose surface expression is Fc epsilon RI gamma independent, replaces Fc gamma RIII during thymic development in these animals. Moreover, subsequent development into CD4+CD8+ double-positive and CD4+CD8- and CD4-CD8+ single-positive subsets appears normal even in the absence of Fc epsilon RI gamma. However, alterations were noted in adult animals among the DN alpha beta TCR+ thymocytes and peripheral splenic DN T cells as well as CD8 alpha alpha + intestinal intraepithelial lymphocytes (iIEL). In contrast to conventional T lymphocytes, which do not express either Fc gamma RIII or Fc epsilon RI gamma, DN alpha beta TCR+ thymocytes and extrathymically derived alpha beta TCR+ and gamma delta TCR+ CD8 alpha alpha + beta- iIEL express TCR which incorporate Fc epsilon RI gamma as one of their subunits. Consistent with this, the TCR levels of these cells are lower than the TCR levels on cells from wild-type C57BL/6 mice. Despite the reduction in the level of surface TCR, the development of these cells was unaltered by the absence of Fc epsilon RI gamma. Thus, we observed alterations in adult DN alpha beta TCR+ thymocytes, splenic DN alpha beta TCR+ and DN gamma delta TCR+ large granular lymphocytes (LGL), and alpha beta TCR+ and gamma delta TCR+ CD8 alpha alpha+beta- iIEL, but no detectable changes in their major fetal thymic developmental pathways. Cultivation of peripheral DN alpha beta TCR+ and DN gamma delta TCR+ cells from Fc epsilon RI gamma-/- mice with interleukin-2 generates LGL which mediate natural killer activity. Unlike LGL from wild-type C57BL/6 mice, LGL from Fc epsilon RI gamma-/- mice lack Fc gamma RIII expression and could not mediate antibody-dependent cellular cytotoxicity through Fc gamma RIII.

Semisynthetic echinocandins affect cell wall deposition of Pneumocystis carinii in vitro and in vivo

Cyclic lipodepsipeptide compounds of the echinocandin class exhibit broad-spectrum antifungal activity and have been shown to be effective in the treatment of Pneumocystis carinii pneumonia in laboratory animal models. Previous studies have led investigators to propose that these compounds, active against fungal cell walls, are selectively active against the cyst forms of P. carinii. We demonstrate that a semisynthetic, water-soluble echinocandin analog, LY307853, is effective in reducing the number of all life cycle forms of P. carinii and is more effective in mice immunosuppressed with monoclonal antibody to L3T4+ cells than in mice immunosuppressed with dexamethasone. Treatment of P. carinii isolates with LY307853 in a short-term in vitro culture model resulted in cytoarchitectural alterations suggesting that this echinocandin may interfere with the export of surface glycoprotein and the formation of the tubular elements normally found on the surfaces of trophic forms. The cytoarchitectural changes in trophic forms treated in vitro with LY307853 were also observed in trophic forms in the lung tissue of rats treated with a closely related echinocandin analog, LY303366.

Activation mediated by RP105 but not CD40 makes normal B cells susceptible to anti-IgM-induced apoptosis: a role for Fc receptor coligation

Signals through the B cell antigen receptor lead to a variety of cellular events such as activation, anergy, and apoptosis. B cells select these outcomes to establish and maintain self-tolerance, and to mount adequate antibody responses. However, it is not fully understood how one and the same signal causes such different consequences. In the present study, we have studied the effect of activation signals on the outcome of responses to antigen receptor ligation. Two distinct growth-promoting signals were used to activate B cells. Ligation of either RP105, a newly discovered B cell surface molecule, or the CD40 molecule, drove B cells to proliferate. Resultant blastic cells were then exposed to anti-immunoglobulin M (IgM). Blast cells that had been stimulated with anti-RP105 ceased growing and underwent apoptosis after cross-linking of surface IgM. Coligation of the Fc gamma receptor IIB with surface IgM augmented, rather than aborted, this response. In contrast to RP105-activated B cells, blast cells that had been activated by CD40 ligation were unaltered by anti-IgM. On the other hand, CD40-activated B cells became extremely susceptible to Fas-mediated apoptosis, whereas RP105-activated B cells were much less sensitive. Anti-IgM-induced apoptosis in RP105 blasts was independent of Fas, because it was demonstrable with Fas-deficient MRL-lpr/lpr mice. These results demonstrate that the nature of an initial activation signal has a great influence on the fate of activated B cells after (re)engagement of the antigen receptor. RP105, as well as CD40, may be important in this life/death decision.

Duration of TCR stimulation determines costimulatory requirement of T cells

Current models suggest that T cells that receive only signal-1 through antigenic stimulation of the T cell receptor (TCR) become anergic, but will mount an immune response when a costimulatory signal-2 is provided. Using mice deficient for an important costimulatory molecule, CD28, we show that a transient signal-1 alone, either through infection with an abortively replicating virus, or through injection of viral peptide, anergizes CD8+ T cells, demonstrating the biological relevance of T cell anergy in vivo. However, in the absence of CD28, continued presence of signal-1 alone, either through prolonged viral replication or repeated injection of peptide, prevents the induction of anergy and generates a functional T cell response in vivo.

CD4-dependent and -independent association of protein tyrosine kinases to the T cell receptor/CD3 complex of CD4+ mouse T lymphocytes

Tyrosine phosphorylation of different substrates is the earliest intracellular signal detected after T cell receptor (TcR) ligation. Several tyrosine kinases have been detected associated to the CD3-TcR complex in stimulated or unstimulated cells, including p56lck, p59fyn and ZAP-70. We have observed, in one mouse T helper CD4 T cell line, that most TcR- or CD3-associated tyrosine kinase activity comes from CD4:p56lck (Diez-Orejas, R., Ballester, S., Feito, M. J., Ronda, M., Ojeda, G., Criado, G., Portolés, P. and Rojo, J. M., EMBO J. 1994. 13: 90). To analyze whether this is a major way of tyrosine kinase association to the TcR in normal CD4+ T cells, we examined the nature and mode of association of tyrosine kinases to the TcR complex in normal spleen CD4+ T lymphocytes. Our results show that, in normal CD4+ T lymphocytes, as in CD4+ T cell lines, there is a stable and readily detectable association between CD4:p56lck and the TcR/CD3 complex, as determined by in vitro kinase activity in immunoprecipitates from cell lysates. However, TcR/CD3 complexes from nature CD4+ lymphocytes have detectable amounts of p56lck associated in a CD4-independent manner, as shown by immunodepletion of the lysates with anti-CD4 antibodies. In addition, TcR/CD3 also bind p59fyn regardless of the presence of CD4. Conversely, we have observed that CD4 co-precipitates small quantities of p56fyn in a TcR/CD3-independent manner. Overall, our data suggest the existence of different possible molecular complexes between TcR/CD3, CD4 and their attending kinases, as well as some quantitative and qualitative differences between CD4+ T cells and CD4+ T cell lines in kinase association to the TcR/CD3 complex.

The two membrane proximal domains of CD4 interact with the T cell receptor

During T cell activation, CD4 is intimately involved in colocalizing the T cell receptor (TCR) with its specific peptide ligand bound to class II molecules of the major histocompatibility complex (MHC). Previously, the COOH-terminal residues, Trp62/63, which flank the immunodominant epitope of hen egg lysozyme (HEL 52-61), were shown to have a profound effect on TCR recognition. CD4 maintains the fidelity of this interaction when short peptides are used. To determine which portion of CD4 was responsible for this effect, a series of CD4 mutants were made and transfected into CD4 loss variants of two HEL 52-61-specific T cell hybridomas. Surprisingly, some CD4 mutants that failed to interact with MHC class II molecules (D2 domain mutant) or with p56kk (cytoplasmic-tailless mutant) restored responsiveness. Nevertheless, a significant reduction in association between cytoplasmic-tailless CD4 and the TCR, as determined by fluorescence resonance energy transfer, was observed. Thus, neither colocalization of CD4 and the TCR nor signal transduction via CD4 was solely responsible for the functional restoration of these T cell hybridomas by wild-type CD4. However, substitution of the two membrane proximal domains of murine CD4 (D3 and D4) with domains from human CD4 or intercellular adhesion molecule 1 not only abrogated its ability to restore function, but also substantially reduced its ability to associate with the TCR. Furthermore, the mouse/human CD4 chimera had a potent dominant negative effect on T cell function in the presence of equimolar concentrations of wild-type CD4. These data suggest that the D3/D4 domains of CD4 may interact directly or indirectly with the TCR-CD3 complex and influence the signal transduction processes. Given the striking structural differences between CD4 and CD8 in this region, these data define a novel and unique function for CD4.

TCR activation of ZAP70 is impaired in CD4+CD8+ thymocytes as a consequence of intrathymic interactions that diminish available p56lck

The fate of developing CD4+CD8+ thymocytes is determined by signals transduced through surface TCR complexes. Here, we report that cross-linking of TCR on CD4+ CD8+ thymocytes fails to activate ZAP70 protein tyrosine kinase and fails to initiate downstream signaling events, unless the TCR are coaggregated with surface coreceptor molecules. TCR signaling in CD4+CD8+ thymocytes is impaired because the number of available p56lck molecules is diminished by intrathymic CD4-Ia interactions that initially activate p56lck molecules, which are subsequently degraded. As a consequence of intrathymic CD4-Ia interactions, TCR zeta chains are initially phosphorylated to recruit ZAP70 molecules, but the recruited ZAP70 molecules are not subsequently phosphorylated, resulting in TCR complexes that are stably associated with inactive ZAP70 molecules. Thus, intrathymic interactions that diminish p56lck regulate TCR signaling thresholds and affect TCR structure in developing CD4+CD8+ thymocytes.

Long-lasting CD8 T cell memory in the absence of CD4 T cells or B cells

The cellular basis of immunological memory has been a debated issue. It is not clear whether CD8 T cell memory is maintained by long-lived cells or by specific or nonspecific restimulation. Here, we have approached the question from a different angle, asking whether the cellular interactions that are required to maintain memory are the same as those necessary to activate cytotoxic T lymphocytes. We studied the CD8 memory response to the male antigen H-Y in mice deficient in CD4 cells, or B cells and found that memory in these mice was virtually unimpaired. These results suggest that CD8 memory is CD4 independent and that there is no requirement for long term retention of immune complexes on follicular dendritic cells, nor for B cells as antigen-presenting cells.

Circumventing genetic restriction of protection against malaria with multigene DNA immunization: CD8+ cell-, interferon gamma-, and nitric oxide-dependent immunity

Despite efforts to develop vaccines that protect against malaria by inducing CD8+ T cells that kill infected hepatocytes, no subunit vaccine has been shown to circumvent the genetic restriction inherent in this approach, and little is known about the interaction of subunit vaccine-induced immune effectors and infected hepatocytes. We now report that immunization with plasmid DNA encoding the plasmodium yoelii circumsporozoite protein protected one of five strains of mice against malaria (H-2d, 75%); a PyHEP17 DNA vaccine protected three of the five strains (H-2a, 71%; H-2k, 54%; H-2d, 26%); and the combination protected 82% of H-2a, 90% of H-2k, and 88% of H-2d mice. Protection was absolutely dependent on CD8+ T cells, INF-gamma, or nitric oxide. These data introduce a new target of protective preerythrocytic immune responses, PyHEP 17 and its P. falciparum homologue, and provide a realistic perspective on the opportunities and challenges inherent in developing malaria vaccines that target the infected hepatocyte.

Populations of thymocytes and peripheral blood leucocytes in leukaemia-bearing mice treated with G-CSF

The influence of granulocyle-colony stimulating factor (G-CSF) on thymocyte subsets and peripheral blood leucocytes in leukaemia L1210-bearing mice was evaluated. Leukaemia-bearing mice have a markedly reduced L3T4+Lyt2+ thymocyte subpopulation. We observed "correction" of relative values of thymocyte subpopulations induced by treatment of mice with a G-CSF preparation. The suggestion is presented that this could result from liberation of lymphocyte T precursor cells from the bone marrow and increased homing of them into the thymus. The direct or indirect influence of G-CSF on the L3T4+Lyt2+ subpopulation of thymocytes is discussed.

Different superantigens interact with distinct sites in the Vbeta domain of a single T cell receptor

CD4 T cell receptors (TCRs) recognize antigenic peptides presented by self major histocompatibility complex (MHC) class II molecules as well as non-self MHC class II molecules. The TCRs can also recognize endogenous retroviral gene products and bacterial toxins known collectively as superantigens (SAGs) that act mainly on the Vbeta gene segment-encoded portion of the Vbeta domain; most SAGs also require MHC II class for presentation. We have studied the interaction of the TCR from a well-characterized CD4 T cell line with SAGs by mutational analysis of its Vbeta domain. This appears to separate viral (v)SAG from bacterial (b)SAG recognition. T cells having a TCR with glycine to valine mutation in amino acid residue 51 (G51V) in complementarity determining region 2 of the TCR Vbeta domain fail to respond the bSAGs staphylococcal enterotoxin B (SEB), SEC1, SEC2, and SEC3, whereas they retain the ability to respond to non-self MHC class II molecules and to foreign peptides presented by self MHC class II molecules. It is interesting to note that T cells expressing mutations of both G51V and G53D of V beta regain the response to SEB and partially that to SEC1, but do not respond to SEC2, and SEC3, suggesting that different bacterial SAGs are viewed differently by the same TCR. These results are surprising, because it has been generally believed that SAG recognition by T cells is mediated exclusively by hypervariable region 4 on the exposed, lateral face of the TCR Vbeta domain. Response to the vSAG Mtv-7 was generated by mutation in Vbeta residue 24 (N24H), confirming previously published data. These data show that the vSAG Mtv-7 and bSAGs are recognized by different regions of the TCR Vbeta domain. In addition, various bSAGs are recognized differently by the same TCR. Thus, these mutational data, combined with the crystal structure of the TCR beta chain, provide evidence for distinct recognition sites for vSAG and bSAG.

Presence of hematopoietic stem cells in the adult liver

Recently, cases have been reported in which a mixed chimeric state of blood cells is established after liver transplantation. Because the established chimerism may have aided in the induction of donor-specific tolerance, the mechanism responsible for this chimerism is of clinical importance. To establish this, we examined cells in adult mouse liver and identified the presence of c-kit+ Sca-1+ Lin(lo/-) cells. These cells were capable of forming in vivo as well as in vitro colonies. Furthermore, the cells could reconstitute bone marrow of lethally irradiated recipient mice for at least 12 months. These data obtained from the mouse study strongly suggest that hematopoietic stem cells residing in the donor liver are responsible for mixed chimerism and maintenance of tolerance after liver transplantation.

The extracellular domain of CD45 controls association with the CD4-T cell receptor complex and the response to antigen-specific stimulation

The CD45 tyrosine phosphatase plays an important role in regulating T lymphocyte activation, but the function of the different isoforms of CD45 is not known. T cell transfectants have been prepared that express individual CD45 isoforms in cells with a well-defined T cell receptor (TCR) from the D10 T helper 2 clone. We find that cells bearing low molecular weight CD45 isoforms are far more efficient in responding to stimulation with peptide and antigen-presenting cells compared with cells bearing high molecular weight CD45 isoforms. One hypothesis for the preferential activation of cells that express low molecular weight CD45 isoforms is that they interact with other cell surface antigens important in TCR signaling, altering their phosphorylation status and affecting the character of the signal transduction pathway. In this report, using cells expressing single isoforms, we demonstrate that low molecular weight isoforms of CD45 preferentially associate with CD4 and the TCR complex compared with high molecular weight isoforms. The molecular basis for this interaction was further examined using a glycosyl phosphatidyl inositol (GPI)-linked form of CD45Null (lacking tyrosine phosphatase domains), which preferentially associated with CD4 compared with GPI-linked CD45ABC, and cytoplasmic tail mutants of CD4, which retained the ability to coassociate. Using this panel of transfectants, it is clear that the interaction between CD4 and CD45 does not require the cytoplasmic domains of CD45, but is dependent on the specific external domain of the various isoforms: low molecular weight species were more likely to associate with the CD4-TCR complex than the higher molecular weight isoforms, and their ability to coassociate correlated with the magnitude of the response to specific antigen.

The effect of erythropoietin administration on murine bone marrow chimeras

All patients develop anemia after autologous or allogeneic bone marrow transplantation and red blood cell transfusion is almost always required in the post-transplant period. Recently Epo therapy has been employed in the setting of bone marrow transplantation. As bone marrow transplant patients typically suffer from malignancies and are immunocompromised, further immunosuppression should be avoided. Recent reports have suggested that Epo may modulate immune response. We have studied the effects of Epo on immune response in murine bone marrow chimeras. Epo administration resulted in an increase in hematocrit. There was no significant alteration in lymphocyte numbers, although a shift in lymphocytes toward T cell predominance was observed. Epo administration resulted in enhanced cell proliferation in response to T and B cell mitogens, although no alteration in cytotoxicity or natural killer cell activity was observed. No example of Epo-induced impaired immunity was observed.

Identical genetic control of MLC reactivity to different MHC incompatibilities, independent of production of and response to IL-2

The inbred strain STS/A exhibits a higher proliferative response in the mixed lymphocyte culture (MLC) to stimulator cells of all 11 tested inbred mouse strains with 10 different major histocompatibility complex (MHC) haplotypes, as well as to stimulation with IL-2 than does the strain BALB/cHeA. However, alloantigen-stimulated BALB/c cells produce more IL-2 than STS/A cells. To study the genetic basis of these differences, we used 20 recombinant congenic strains (RCS) of the CcS/Dem series. Each of these CcS/Dem RC strains contains a different subset of about 12.5% of genes from the STS/A strain and the remaining approximately 87.5% of BALB/c origin genes. As a result the multiple non-linked genes responsible for phenotypic differences between BALB/c and STS/A became separated into different CcS/Dem strains. The strain distribution pattern (SD) of high or low MLC response of individual CcS/Dem strains to stimulator cells of four different strains was almost identical, indicating that differences in responsiveness, rather than the alloantigenic difference itself, determine the magnitude of the response, and that the responsiveness to different alloantigens is largely controlled by the same genes. The SDP of IL-2 stimulation was different from that of MLC responsiveness. The differences in the proliferative responses observed among individual CcS/Dem strains were not due to differences in numbers of CD3+, CD4+ or CD8+ cells or to the observed differences in IL-2 production, and hence they likely reflect genetically determined intrinsic properties of T cells. These results show that a set of non-linked genes controls proliferative responses in MLC irrespective of the MHC haplotype of the stimulator cells, and that stimulation with IL-2 and production of IL-2 are controlled by different subsets of genes. Since the genomes of all RCS are extensively characterized by microsatellite markers, they can be used to map the genes controlling proliferative responsiveness to stimulation with alloantigens and IL-2.

Thymus involution induced by mouse hepatitis virus A59 in BALB/c mice

Mouse hepatitis virus A59 (MHV-A59) infection of adult BALB/c mice induced a severe, transient atrophy of the thymus. The effect was maximal at 1 week after infection, and thymuses returned to normal size by 2 weeks after infection. There was no effect of glucocorticoids, since thymus atrophy was also found in adrenalectomized, infected mice. In infected thymus, immature CD4+ CD8+ lymphocytes were selectively depleted, and apoptosis of lymphocytes was increased. The MHV receptor glycoprotein MHVR was detected on thymus epithelial cells but not on T lymphocytes. In a small number of stromal epithelial cells, but in very few lymphocytes, the viral genome was detectable by in situ hybridization. These observations suggested that MHV-A59-induced thymic atrophy results not from a generalized lytic infection of T lymphocytes but rather from apoptosis of immature double-positive T cells that might be caused by infection of a small proportion of thymus epithelial cells or from inappropriate secretion of some factor, such as a cytokine.

Successful T cell priming in B cell-deficient mice

B cells are an abundant population of lymphocytes that can efficiently capture, process, and present antigen for recognition by activated or memory T cells. Controversial experiments and arguments exist, however, as to whether B cells are or should be involved in the priming of virgin T cells in vivo. Using B cell-deficient mice, we have studied the role of B cells as antigen-presenting cells in a wide variety of tests, including assays of T cell proliferation and cytokine production in responses to protein antigens, T cell killing to minor and major histocompatibility antigens, skin graft rejection, and the in vitro and in vivo responses to shistosome eggs. We found that B cells are not critical for either CD4 or CD8 T cell priming in any of these systems. This finding lends support to the notion that the priming of T cells is reserved for specialized cells such as dendritic cells and that antigen presentation by B cells serves distinct immunological functions.

Emergence in C kappa knockout mice of a diverse cytotoxic T lymphocyte repertoire that recognizes a single peptide from the immunoglobulin constant kappa light chain region

Allotype- or idiotype-specific CD4+ T cells have been reported to recognize immunoglobulin (Ig) peptides presented by class II molecules. In contrast, few data are available concerning the generation of Ig peptide-specific CD8+ T cells. We have therefore investigated whether T-depleted spleen cells from Ig kappa light chain-expressing 129/Sv mice (129 kappa +/+) could induce, in C kappa knockout mice (129 kappa -/-), the generation of Ig constant kappa light chain region (C kappa)-specific cytotoxic T lymphocytes (CTL). The determination of TCR beta chain expressed by nine CTL clones, together with the use of a library of overlapping peptides spanning the whole C kappa sequence, show that the B cells from kappa +/+ mice are able to elicit in C kappa knockout mice, the emergence of a diverse CTL repertoire that recognizes one single C kappa peptide presented by the H-2Kb class I molecule. In addition, these data support the notion that B cells are able to process and present on their class I molecules, peptides generated from their own kappa light chains.

Adoptive transfer of T lymphocytes to T-cell-depleted mice inhibits Escherichia coli translocation from the gastrointestinal tract

Bacterial translocation is defined as the passage of viable bacteria from the gastrointestinal (GI) tract to extraintestinal sites, such as the mesenteric lymph node (MLN), spleen, liver, kidneys, and blood. Previously, we reported that depletion of CD4+ and/or CD8+ T cells promotes bacterial translocation from the GI tract to the MLN. In the present study, CD4+ and/or CD8+ T cells, harvested from donor mice, were adoptively transferred to mice previously depleted of T cells by thymectomy plus intraperitoneal injection of rat anti-mouse T-cell monoclonal antibodies. The adoptively transferred CD4+ and/or CD8+ T cells inhibited the translocation of Escherichia coli from the GI tract. Migration of the adoptively transferred T cells to the spleens and MLNs of the recipient mice was determined by utilizing Thy 1.1+ donor cells adoptively transferred into mice whose cells express the Thy 1.2 marker. These results provide further evidence of the importance of T cells in the host immune defense against bacterial translocation from the GI tract.

CD4 and CD45 regulate qualitatively distinct patterns of calcium mobilization in individual CD4+ T cells

An early consequence of T cell activation is an increase in intracellular calcium concentration. Recent advances in video laser microscopic techniques enable the examination of individual cells over time following stimulation. Such studies have revealed that cells can undergo qualitatively distinct patterns of calcium mobilization, suggesting that different patterns of calcium flux may be associated with different signaling pathways and may differentially affect late events in cell activation. In this report, we identify distinct patterns of calcium mobilization in CD4+ T cells following the antibody-mediated cross-linking of either CD3 or CD4, or following the cross-linking of both CD3 and CD4 simultaneously. These effects can be further modified by the cross-linking of CD45. We find that antibody cross-linking of CD3 alone induces a single spike in the vast majority of cells shortly after the addition of the cross-linking antibody. In contrast, cross-linking CD4 alone induces a delayed pattern of repetitive calcium spikes which are decreased in amplitude compared to CD3 cross-linking. Simultaneous cross-linking of CD3 and CD4 induces a sustained increase in intracellular calcium mobilization which is dependent on the presence of extracellular calcium. This sustained increase in intracellular calcium concentration is also seen following physiologic cross-linking of CD3 and CD4 after T cell interaction with specific antigen and antigen-presenting cells. Finally, the simultaneous cross-linking of CD45, CD3 and CD4 abrogates the sustained increase in calcium seen following CD3 and CD4 cross-linking. These results suggest that the qualitative nature of T cell receptor signaling can be modulated by the molecular association of other signaling molecules, which may be part of the T cell receptor complex or not.

Intrathymically expressed c-kit ligand (stem cell factor) is a major factor driving expansion of very immature thymocytes in vivo

To investigate the role of the receptor-type tyrosine kinase, c-kit and its ligand, stem cell factor (SCF) in T cell development, we analyzed c-kit (W/W) and SCF (SI/SI) deficient mice. We also engrafted wild-type or SCF-deficient fetal thymi onto wild-type recipient mice and analyzed the rate of proliferation by in vivo bromodeoxyuridine labeling. The results show that the most immature thymocyte compartment defined as CD3-CD4-CD8- is significantly reduced in SI/SI grafts and W/W thymi compared with wild-type counterparts. Also, the expansion rate of these immature thymocytes in SI/SI graft is reduced by -50%. These experiments provide direct evidence for an important role for c-kit-SCF interactions in expansion of very early thymocytes.

The peripheral T cell repertoire: independent homeostatic regulation of virgin and activated CD8+ T cell pools

Mature T cells may be produced in the thymus, or by expansion in the periphery. While thymus output of virgin cells ensures repertoire diversity, peripheral expansion increases the size of rare clones, and thus the efficiency of immune responses. We studied the role of both phenomena in the generation of the CD8+ T cell pool using RAG-/- female mice expressing a transgenic T cell receptor specific for the male antigen; nude mice injected with peripheral T cells; and euthymic irradiated chimeras injected with bone marrow and mature T cells. Our results show that the total number of virgin and activated T cells, each constituting about half of the peripheral T cell pool, was regulated independently, revealing an efficient mechanism to maintain repertoire diversity while optimizing the immune response.

No evidence for TCR V beta repertoire changes influencing disease protection in E-transgenic NOD mice

In order to study whether positive selection of T cells plays any role in the MHC-dependent protection from diabetes in the non-obese-diabetic (NOD) mouse, the T cell V beta repertoire has been studied in NOD mice and in NOD mice either transgenic for the wildtype MHC class II E alpha gene, or for delta Y, a promotor-mutagenized E alpha gene with a restricted tissue expression. The E alpha transgenic line is protected from both insulitis and diabetes. The delta Y transgenic line is neither protected from insulitis nor from diabetes, although it can perform both positive and negative E-mediated selection in the thymus. The V beta repertoire was studied in the pancreatic lymph nodes as these drain the area which is the target for the autoimmune attack. We see no evidence for E alpha TCR V beta repertoire differing from both nontransgenic NOD mice and delta Y mice despite its striking difference in susceptibility to autoimmunity. We conclude that none of the differences in the TCR V beta repertoire of E alpha-transgenic NOD mice hitherto observed are likely to explain the protective effect of E molecule expression in NOD mice.

Direct physical interaction involving CD40 ligand on T cells and CD40 on B cells is required to propagate MMTV

The propagation of mouse mammary tumor virus (MMTV) has been analyzed in mice defective for expression of CD40 ligand (CD40L). Mice with endogenous viral superantigen (SAG) delete T cells with cognate V beta independent of CD40L expression. Nevertheless, CD40L-mice do not show deletion of cognate T cells after being exposed to infectious MMTV and have greatly diminished viral replication. The response of CD40L- T cells to SAG in vitro is also impaired, but can be reconstituted by adding B cells activated by recombinant CD40L to express costimulatory molecules. Thus, direct CD40L-dependent B cell activation appears to be a critical step in the life cycle of MMTV. The initial step in SAG-dependent T cell activation, and hence the MMTV life cycle, may be mediated by non-B cells, because splenocytes from B cell-deficient SAG-transgenic mice are able to activate cognate T cells.

Mechanism of enhanced antigen presentation by B cells activated with anti-mu plus interferon-gamma: role of B7-2 in the activation of naive and memory CD4+ T cells

B cells activated with anti-mu antibody plus interferon (IFN)-gamma exerted strong antigen presentation activity for T cell proliferation. The enhanced antigen presentation function was shown to be due to the increase in B7-2 expression. When B cells were stimulated with anti-mu, expression of MHC major histocompatibility complex class II, heat-stable antigen (HSA), ICAM-1 and B7-2 was increased. The presence of IFN-gamma further augmented the expression of B7-2 on anti-mu-stimulated B cells. B7-1 was not expressed on B cells under these conditions. The participation of B7-2 in the elicitation of the proliferative response of T cells was confirmed by the inclusion of anti-B7-2 antibody in cultures. The enhanced expression of either HSA or ICAM-1 was shown not to play a major role in the increased B cell antigen presentation capacity. The major T cell population responding to this activated B cell antigen presentation was shown to be CD44low naive CD4+ T cells, whereas CD45RBlow memory CD4+ T cells responded only weakly. The difference in proliferative responses between naive and memory CD4+ T cells was explained by the different efficiency in IL-2 production of these cell populations in response to antigen presentation by B cells activated by anti-mu plus IFN-gamma. These results suggest that IFN-gamma plays an important role in recruitment of naive T cells for an immune response.

Mouse embryo fibroblasts transformed by activated ras or dominant-negative p53 express cross-reactive tumor rejection antigens

To study the immune response against oncogene-transformed tumors, C3H/HcN mouse embryo fibroblasts (MEF) were transfected with an activated allele of the H-ras proto-oncogene VaII2 and a dominant-negative allele of the murine p53 tumor suppressor gene VaII35. Transformed cell lines were derived and found to be tumorigenic in syngeneic mice. Immunization with irradiated p53 + ras-transformed MEF, but not primary MEF or unrelated syngeneic cells, protected mice from subsequent challenge with live tumor cells. The role of different immune cell subsets in the effector phase of anti-tumor immunity induced by immunization with p53 + ras-transformed MEF was investigated by in vivo antibody depletion experiments. Immunized mice depleted of CD8+ T, NK or B cells were resistant, but depletion of CD4+ T cells rendered mice susceptible to tumorigenic challenge. In contrast to the tumor-specific immune responses mounted against most chemically or UV-induced tumors, a series of independently derived p53 + ras-transformed MEF were cross-reactive in tumor rejection assays. In addition, immunization with C3H-derived L-929 cell lines expressing single gene products H-ras or p53 did not protect mice against tumorigenic challenge with p53 + ras-transformed tumors. However, MEF transformed by expression of either H-ras or p53 were cross-protective in vivo. Our data suggest that the p53 + ras-transformed MEF share tumor rejection antigens which are also induced by single gene transformation of the parental primary cell but are not the products of oncogenic ras or p53 protein.

Fibroblasts as efficient antigen-presenting cells in lymphoid organs

Only so-called "professional" antigen-presenting cells (APCs) of hematopoietic origin are believed capable of inducing T lymphocyte responses. However, fibroblasts transfected with viral proteins directly induced antiviral cytotoxic T lymphocyte responses in vivo, without involvement of host APCs. Fibroblasts induced T cells only in the milieu of lymphoid organs. Thus, antigen localization affects self-nonself discrimination and cell-based vaccine strategies.

Viral peptide specific cytotoxic T lymphocytes are of high avidity to host-MHC but only low avidity to donor-MHC after allogeneic bone marrow transplantation

In the thymus maturing T lymphocytes are positively selected for efficient interaction with self-MHC molecules. Consequently, mature peripheral T cells recognize foreign (microbial) antigens in association with self-MHC molecules (known as MHC restricted recognition). In experimental bone marrow transplantation (BMT) lymphohaemopoietic stem cells from an MHC disparate donor transfused to an irradiated host give rise to mature T lymphocytes with host-MHC restriction specificity. While experiments with T cell receptor transgenic mice have largely confirmed this concept, many studies using genetically unmanipulated animals analysing polyclonal T cell repertoires have also shown donor-MHC restricted T cell activities after allogeneic BMT. To analyse this discrepancy we generated 18 virus specific cytotoxic T cell (CTL) clones, 16 from F1 into parent and two from fully allogeneic bone marrow chimeras, and analysed the MHC restriction specificity in proliferation and cytotoxicity assays. The cytotoxicity of all the clones was primarily host-MHC restricted. However, the CTL clones proliferated to viral antigen presented by both donor- or host-MHC. Our model allowed CTL cloning by cross-specific stimulation with antigen plus either donor-MHC or else host-MHC. Interestingly, even the 14 CTL clones which had been raised with donor-MHC systematically killed host-MHC but not donor-MHC expressing cells. Thus, after BMT, CTLs may proliferate crossreactively to donor-MHC but cytolysis is predominantly directed to host-MHC expressing cells. Since lytic CTL activity probably reflects high avidity CTL interaction necessary for viral clearance in vivo, the data suggest that the donor-MHC restricted CTL activity may not be protective and that virus may escape CTL surveillance in donor cells.

Inflammatory response following intranasal infection with Mycobacterium avium complex: role of T-cell subsets and gamma interferon

The role of CD4+ and CD8+ T cells in the response to intranasal infection with a Mycobacterium avium complex isolate (MAC) was investigated. Depletion of CD4+ T cells by injected antibody exacerbated infection in the lung, spleen, and liver. There were decreased numbers of inflammatory cells in the lungs of CD4-depleted mice and a significant decrease in lung cytotoxic activity. The neutrophil response was unaffected, and in CD4-depleted mice, unlike intact infected mice, these cells were found with large numbers of associated MAC. Purified CD4+ splenic T cells produced gamma interferon (IFN-gamma) in vitro in response to MAC antigen. IFN-gamma production by cultured spleen, lung, or mediastinal lymph node cells was markedly reduced in CD4-depleted mice. In contrast, CD8+ T cells did not produce IFN-gamma in vitro, and depletion of CD8+ T cells from infected mice had no effect on bacterial growth or lung cell activation. Depletion of IFN-gamma by injected monoclonal antibody had effects similar to those of CD4 depletion, namely, exacerbation of infection and decreased lung cell cytotoxicity. We conclude that CD4+ T cells are the main T cells involved in the lung response to MAC infection and that this response is at least partially dependent on the production of IFN-gamma.

Transforming growth factor-beta 1-induced expression of the mucosa-related integrin alpha E on lymphocytes is not associated with mucosa-specific homing

The integrin alpha E (HML-1, alpha IEL, alpha M290) is largely expressed on lymphocytes in epithelial sites, especially the gut mucosa. We investigated whether alpha E has any role in homing or delineates a phenotype with distinct migratory behavior. Lymph node T cells were stimulated for 5 days with anti-CD3 in the presence or absence of transforming growth factor (TGF)-beta 1 to generate alpha E+ or alpha E- cells, respectively. The two populations were then tested for their homing properties in mice. Both alpha E+ (TGF-beta-treated) and alpha E- (control) cells of either CD4+ or CD8+ subset had a low capacity to enter the gut and showed the same homing behavior with respect to a variety of other organs. The same was true for alpha E+ and alpha E- cells that had been briefly stimulated with anti-CD3 (24 h) and then allowed to return to a resting state before injection, though in this case both populations showed a greater capacity to recirculate through lymphoid tissue than was seen with fully activated cells. The results indicate that alpha E beta 7 does not act as a homing receptor, and that the expression of the site-specific marker alpha E does not correlate with a distinct homing behavior.

T cells made deficient in interleukin-2 production by exposure to staphylococcal enterotoxin B in vivo are primed for interferon-gamma and interleukin-10 secretion

The superantigen staphylococcal enterotoxin B (SEB) induces a defect in interleukin (IL)-2 production by T cells expressing specific T cell receptor V beta domains. The present study was undertaken to determine the capacity of T cells, made deficient in IL-2 production by exposure to SEB in vivo, to secrete interferon (IFN)-gamma and IL-10 and to induce pathology upon SEB rechallenge. For this purpose, BALB/c mice received two intraperitoneal injections of 100 micrograms SEB with a 48-h interval. First, we compared peak serum levels of IL-2, IFN-gamma and IL-10 after SEB rechallenge with those measured after a single SEB injection in control mice. The expected defect in IL-2 production in SEB-pretreated mice was associated with a major increase in IL-10 and IFN-gamma levels which were about fivefold higher than in controls. Experiments in mice depleted of CD4+ or CD8+ cells as well as studies in which purified T cell populations were rechallenged with SEB in vitro indicated that both CD4+ and CD8+ cells from SEB-pretreated mice were primed for IL-10 and IFN-gamma production. Furthermore, SEB-pretreated mice were sensitized to the toxic effects of the superantigen as indicated by a 30-70% lethality rate (vs. 0% in naive mice) within 48 h after SEB rechallenge. IFN-gamma was involved in the lethal syndrome as it could be prevented by injection of neutralizing anti-IFN-gamma monoclonal antibody. We conclude that SEB-reactive T cells made deficient for the production of IL-2 by exposure to SEB in vivo are primed for IFN-gamma and IL-10 production, and that IFN-gamma up-regulation is involved in the shock syndrome occurring upon SEB rechallenge.

Suppression of immune parameters in animal models of morphine dependence

Implantation of pellets containing 75 mg of morphine induced short term (4 day) morphine dependence and markedly reduced total number of spleen cells of BALB/c mice, without affecting total body or liver weight. Polyclonal responses induced by anti-CD3 antibodies, Concanavalin A or Escherichia coli lipopolysaccharide in the remaining spleen cells of morphine-treated mice were also inhibited. Cytofluorimetric analysis indicated that the proportion of major functional lymphocyte populations (Ig+, CD3+, CD4+ and CD8+ lymphocytes) were not significantly changed in the spleen from morphine-dependent mice. Furthermore, expression levels of surface Ig, CD3, CD4, and CD8, were similar in spleen cells from control or morphine-treated mice. So, morphine dependence in BALB/c mice under these controlled conditions results in a specific defect in lymphoid cell number and function, with no incidence on body weight or particular lymphocyte subsets.

Stochastic coreceptor shut-off is restricted to the CD4 lineage maturation pathway

Kinetics of mature T cell generation in the thymus of normal or major histocompatibility complex (MHC) class I- or II-deficient mice were studied by the bromodeoxyuridine pulse labeling method. As previously described, the early activation and final maturation phases were found to be synchronous for the two T cell lineages, but CD4+8- cells were generated faster than CD4-8+ cells in MHC class I- and II-deficient mice, respectively. CD8 downregulation started on day 2 after cell proliferation even in the absence of MHC class II expression. CD8 downregulation thus appears to be stochastic at its beginning. By contrast, CD4 shut-off was found totally instructive, as the generation of CD4lo8+ cells with a high TCR density was not observed in class I-deficient mice. The analysis of the V beta 14 TCR frequencies in CD4/8 subsets in normal and MHC-deficient mice confirmed that CD4 and CD8 generation pathways are not symmetrical. These findings show that commitment towards the CD4+8- or CD4-8+ phenotype is controlled at the CD8lo step for the former and at the CD4+8+ double-positive stage for the latter.