PubMed Health⌕ Search

Biomedical subjects

D H Raulet

Publications and source records attributed to D H Raulet.

At least 19 recordsLinked to original sources
PubMed1996

Major histocompatibility complex genes determine natural killer cell tolerance.

Murine natural killer (NK) cell subsets, as defined by expression of members of the Ly49 gene family, discriminate target cells expressing different major histocompatibility complex (MHC) class I alleles. For example, Ly49A+ NK cells lyse H-2b but not H-2d tumor target cells. The specificity arises because Dd on target cells binds to Ly49A, transducing an inhibitory signal into the Ly49A+ NK cells. The capacity of NK cells to discriminate allelic class I determinants raises a key issue: are NK cells self-tolerant, and if so what are the mechanisms that lead to self-tolerance? As previously reported, potentially autoaggressive Ly49A+ NK cells are not clonally deleted in H-2b mice. However, IL-2-cultured Ly49A+ effector cells from H-2b mice exhibit reduced lysis of H-2b (self) concanavalin A blast target cells, compared to Ly49A+ effector cells from H-2d mice. Possible mechanisms accounting for this self-tolerance are addressed in this report. Self-tolerance was not due to anergy of the cells, because the Ly49A+ effector cells from both types of mice lysed beta 2-microglobulin-deficient target cells efficiently and equivalently. These results also suggest that tolerance results from inhibition mediated by beta 2m-dependent H-2b class I molecules. Significantly, blockade of Ly49A on Ly49A+ effector cells from H-2b mice did not restore lysis of H-2b target cells, suggesting that inhibition is not mediated through the Ly49A receptor. Additional experiments suggest that inhibition is also not mediated primarily through the Ly49C receptor. These results suggest that Ly49A+ effector cells from H-2b mice, unlike those from H-2d mice, express inhibitory receptors specific for H-2b molecules that are distinct from Ly49A and Ly49C.

Animals↗
PubMed1996

Major histocompatibility complex class I-dependent skewing of the natural killer cell Ly49 receptor repertoire.

Subsets of mouse natural killer (NK) cells express receptors encoded by the Ly49 gene family that recognize allelic determinants on major histocompatibility complex (MHC) class I molecules. Recognition of self class I molecules typically inhibits NK cell lytic function. The presence of NK cell subsets expressing receptors which are able to discriminate class I alleles raises the possibility that there exist mechanisms to coordinate the NK cell receptor repertoire with the class I molecules of the host. In the present study, we determined the effects of class I gene expression on the frequencies of NK cells expressing three different Ly49 receptors defined by monoclonal antibodies. We show here an MHC-dependent skewing of NK cell subsets expressing multiple Ly49 receptors with specificity for self MHC. The results provide the first evidence that the frequencies of NK cells expressing different Ly49 receptors are determined by the host's MHC molecules. The results also extend previous findings that MHC class I expression influences the cell surface levels of each Ly49 receptor, suggesting an additional mechanism by which MHC molecules may influence the effective specificity of NK cells. Models to account for self tolerance and MHC-controlled repertoire differences are discussed.

Animals↗
PubMed1996

Recognition events that inhibit and activate natural killer cells.

Natural killer (NK) cells exhibit specificity for MHC class I molecules in their interactions with target cells. Instead of activating the cells, the recognition of class I molecules on target cells inhibits NK-cell lytic activity, suggesting that surveillance of normal class I expression by body cells represents a key NK-cell function. Recent advances have been made in identification of the class I specific receptors expressed by NK cells, and in the characterization of their detailed specificity and expression patterns. Other studies are beginning to unravel recognition events that activate NK cells.

Animals↗
PubMed1995

Allelic exclusion of Ly49-family genes encoding class I MHC-specific receptors on NK cells.

An important feature of natural killer (NK) cell activity is the lysis of cells that have extinguished expression of some or all class I major histocompatibility (MHC) molecules. Accordingly, the Ly49A NK-cell antigen receptor has been shown to deliver an inhibitory signal to NK cells on encounter with Dd or Dk class I MHC on target cells. Ly49A belongs to a family of eight or more highly related, tightly linked genes. Expression of Ly49A and Ly49C, another member of the Ly49 family with distinct MHC specificity, define subpopulations of NK cells that are only partly overlapping. The mechanisms regulating the expression of LY49 family members are unknown. We show here that the Ly49A and Ly49C NK-cell receptors are each subject to allelic exclusion. Because Ly49 genes are not thought to undergo DNA rearrangement, allelic exclusion of Ly49 genes could involve a mechanism distinct from that used by B and T lymphocytes and is likely to play an important role in the genesis of a putative NK-cell repertoire specific for class I molecules.

Alleles↗
PubMed1995

The role of c-Myb or a related factor in regulating the T cell receptor gamma gene enhancer.

An enhancer has been localized 3 kb downstream of the C gamma 1 gene segment of the murine TCR-gamma locus. One element, the gamma 3 site, has been shown to be critical for its functional activity. Here we have determined that Myb-related transcription factors bind to the gamma 3 site and appear to be critical for the full activity of the TCR-gamma enhancer. c-myb products can transactivate the gamma 3 site in cell lines that do not ordinarily support enhancer activity of the gamma 3 site. Mutations in the myb site or an adjacent site for core-binding factor(s) prevent transactivation. c-myb expression in various cell lines is consistent with their capacity to activate the gamma 3 enhancer element using transient transfection assays. Therefore, c-Myb or a related factor appears to play an important role in regulating the murine TCR-gamma enhancer.

Animals↗
PubMed1995

Evidence that productive rearrangements of TCR gamma genes influence the commitment of progenitor cells to differentiate into alpha beta or gamma delta T cells.

Two models have been considered to account for the differentiation of gamma delta and alpha beta T cells from a common hematopoietic progenitor cell. In one model, progenitor cells commit to a lineage before T cell receptor (TCR) rearrangement occurs. In the other model, progenitor cells first undergo rearrangement of TCR gamma, delta, or both genes, and cells that succeed in generating a functional receptor commit to the gamma delta lineage, while those that do not proceed to attempt complete beta and subsequently alpha gene rearrangements. A prediction of the latter model is that TCR gamma rearrangements present in alpha beta T cells will be nonproductive. We tested this hypothesis by examining V gamma 2-J gamma 1C gamma 1 rearrangements, which are commonly found in alpha beta T cells. The results indicate that V gamma 2-J gamma 1C gamma 1 rearrangements in purified alpha beta T cell populations are almost all nonproductive. The low frequency of productive rearrangements of V gamma 2 in alpha beta T cells is apparently not due to a property of the rearrangement machinery, because a transgenic rearrangement substrate, in which the V gamma 2 gene harbored a frame-shift mutation that prevents expression at the protein level, was often rearranged in a productive configuration in alpha beta T cells. The results suggest that progenitor cells which undergo productive rearrangement of their endogenous V gamma 2 gene are selectively excluded from the alpha beta T cell lineage.

Animals↗
PubMed1995

Inhibitory effects of class I molecules on murine NK cells: speculations on function, specificity and self-tolerance.

This review addresses the physiological role of class I-mediated inhibition of NK cell lysis. It is suggested that several distinct activating receptors can stimulate NK lysis, all of which can be inhibited by class I molecules on the target cell. Evidence that most or all peptides that bind a class I molecule can cause inhibition is discussed, supporting a model in which NK cells detect loss of class I molecules, rather than loss of specific peptide/class I complexes. Finally, the acquisition of self-tolerance among NK cells is addressed with respect to data suggesting that autoaggressive NK cells are not deleted but rather exhibit altered characteristics which may render them unable to lyse autologous cells.

Animals↗
PubMed1995

Binding of diverse peptides to MHC class I molecules inhibits target cell lysis by activated natural killer cells.

Class I MHC expression by target cells inhibits lysis mediated by natural killer (NK) cells, often in an allele-specific fashion. It has been proposed that NK cell inhibitory receptors recognize complexes of class I molecules with specific cellular peptides that define self, displacement of which would render cells NK sensitive. By loading the mostly empty Dd class I molecules of cell lines deficient in peptide transporter molecules with synthetic or natural Dd-bound peptides, we have demonstrated specific dose-dependent inhibition of the Ly49+ subset of activated NK cells by class I-peptide complexes. Inhibition occurred with most if not all Dd-binding peptides, suggesting that Ly49+ NK cells recognize class I-peptide complexes largely independently of peptide composition. The results suggest a primary role of NK cells in the destruction of cells that have down-regulated or extinguished cell surface expression of some or all class I molecules.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

The role of short homology repeats and TdT in generation of the invariant gamma delta antigen receptor repertoire in the fetal thymus.

Fetal thymic and adult epithelial V gamma 3+ and V gamma 4+ T cells express gamma delta antigen receptors (TCR) with invariant junctions lacking N nucleotides. Using transgenic recombination substrates, we show that di- or trinucleotide repeats, either in the coding region or in P elements, have strong effects on the site of recombination. In other mice bearing a terminal deoxynucleotidyl transferase (TdT) transgene under the control of the CD2 promoter, we found that the frequency of canonical junctions was markedly reduced with a concomitant increase in in-frame noncanonical junctions with N nucleotides. Together, our results show that short homology repeats direct the site of rearrangement and thus play a critical role in the generation of gamma delta T cell receptor canonical junctions. Increased TdT activity in V gamma 3+ T cells has a inhibitory effect on junctional homogeneity in these cells.

Animals↗
PubMed1994

Class I dependence of the development of CD4+ CD8- NK1.1+ thymocytes.

A small subset of functionally active CD4+ CD8- thymocytes express the NK1.1 marker, as do most CD4-CD8- NK1.1+ thymocytes. Previous studies have failed to implicate a role for major histocompatibility complex (MHC) or related molecules in the selection of the CD4+ CD8- NK1.1+ subset. We report here that the development of most of these cells is sharply reduced in class I-deficient mice, but not in class II-deficient mice. Hence, some CD4+ T cells are class I dependent and not class II dependent. Unlike conventional T cells, however, the development of NK1.1+ thymocytes in both the CD4+ CD8- and CD4- CD8- subsets is dependent on class I MHC expression by hematopoietic cells and not thymic epithelial cells. We propose that these populations are selected by nonpolymorphic class Ib or CD1 molecules.

Animals↗
PubMed1994

T-cell immunity. How gamma delta T cells make a living.

New evidence indicates that gamma delta T cells, like alpha beta T cells, provide immunity to infectious diseases; but the two cell types may differ in that MHC molecules may not play a critical role in antigen presentation to most gamma delta T cells.

Animals↗
PubMed1994

Role of IL-6, IL-1, and CD28 signaling in responses of mouse CD4+ T cells to immobilized anti-TCR monoclonal antibody.

Purified CD4+ T cells require TCR engagement and Ag-nonspecific co-stimulatory signals to produce IL-2 and proliferate. A number of recent studies have demonstrated that the interaction of the B7 molecule expressed on APC with the T cell-associated CD28 molecule provides a potent co-stimulatory signal to both freshly isolated CD4+ T cells and cloned Th1 cells. Earlier reports have described the role of cytokines, in particular IL-6 and IL-1, as costimulatory molecules for T cell activation. We previously reported that IL-6 and IL-1 synergize to co-stimulate proliferation of purified mouse CD4+ T cells in conjunction with anti-TCR mAb. In this report we explore the interaction of IL-6, IL-1, and CD28 signaling in the activation of mouse CD4+ T cells, and demonstrate that the co-stimulatory requirements of the cells vary depending on the mode of TCR stimulation. CD28 signaling is not sufficient to co-stimulate responses of high buoyant density CD4+ T cells to anti-TCR-conjugated agarose beads; there is an additional requirement that can be supplied by exogenous IL-6 but not by IL-1. In contrast, in responses to anti-TCR mAb that is passively bound to the bottom of culture wells, CD28 stimulation is sufficient to co-stimulate proliferation, resulting in a very high level of IL-2 production; there is no additional requirement for exogenous IL-6 or IL-1. Possible explanations for the differential requirement for IL-6 in the two systems are discussed. Our results are consistent with the notion that CD28 signaling plays a central role in co-stimulating T cell responses. However, the results also suggest that, depending on the nature of the TCR stimulus, T cell activation may also require additional co-stimulatory signals provided by cytokines.

Animals↗
PubMed1994

Multiple natural killer cell-activating signals are inhibited by major histocompatibility complex class I expression in target cells.

Several lines of evidence indicate that major histocompatibility complex class I molecules expressed by target cells can prevent natural killer cell (NK) lysis, possibly by engaging inhibitory receptors expressed by NK cells. On the other hand it is likely that NK cells must be activated to lysis by the recognition of unidentified NK target structures on target cells. To investigate the relationship between positive activation of NK cells by NK target structures versus inhibition by target cell class I molecules, we have examined various NK/target cell interactions for which the expression of inhibitory class I molecules by the target cells is known. The results suggests that specific properties of the target cell other than the absence of class I expression are necessary to activate NK-mediated lysis. Furthermore, different effector cell populations, i.e. freshly isolated versus interleukin-2 activated NK cells, differ in their capacity to kill class I-deficient lymphoblast target cells. In general, class I-deficient target cells that are resistant to direct lysis by a given NK population can be lysed by the NK cells when the reaction is mediated by antibody-dependent cellular cytotoxicity (ADCC). Most significantly, all types of NK-mediated lysis of lymphoblasts, of tumor cells and of almost any target by ADCC can be inhibited by appropriate class I gene expression in the target cell. These results suggest a model in which lysis by NK cells must be triggered by any one of a set of distinct target cell ligands, but that all of these signals can be overruled by class I-mediated inhibition.

Animals↗
PubMed1994

MHC class I-deficient mice.

A great deal has already been learned from the analysis of beta 2m-mutant mice, but it is clear that a great deal remains to be learned. A significant (though unanticipated) problem with this model system is that it is functionally leaky: residual functional class I expression can be detected in beta 2m- mice, and small numbers of functional CD8+ lymphocytes are present in the animals. In many cases, this has frustrated the initial attempts at obtaining immediate definitive resolution of important questions regarding the function of class I molecules. This has occurred primarily in instances in which the class I-deficient mice fail to express an expected phenotype--for example, in studies showing that beta 2m- mice make adequate protective immune responses against certain intracellular pathogens, and are able to reject some allogeneic tissues with a relatively normal pace. On the other hand, it appears that combining the use of beta 2m- mice with other methods (for example, antibody-mediated depletion of CD8+ T cells) is usually adequate to circumvent these difficulties. It remains to be seen whether other better class I deficiencies can be engineered--for example, large deletions of class I genes or mutations in transcription factors essential for class I gene expression. The extent of immunocompetence of beta 2m- mice was somewhat surprising. It was widely expected that class I-deficient mice would be exquisitely sensitive to many viral infections, though the results indicate that sensitivity varies dramatically with the virus and conditions of infection. However, it appears that in lieu of one major arm of the immune system, compensatory immune mechanisms are in many cases able to deal with infection. Similar conclusions are developing from the analysis of several other recently generated mutant mice. Nevertheless, the results indicate a very important role for class I-directed responses in clearing infections mediated by various viral and parasitic agents, particularly in the case of more severe conditions of infection. Although the class I-deficient mice were initially considered primarily a vehicle for analysis of the role of CD8+ T cells, evidence is accumulating that they manifest deficiencies in several other types of lymphocytes, including NK cells, TCR alpha beta+CD4-CD8- cells, and a subset of TCR gamma delta+ cells. This has been a boon for analysis of the development of these cells, but at the same time it has created difficulties in assigning a biological effect of the mutation to a specific lymphocyte deficiency.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

CD28-induced costimulation of T helper type 2 cells mediated by induction of responsiveness to interleukin 4.

Type 1 and type 2 cloned T helper (Th) cells are believed to require different antigen-presenting cell (APC)-derived costimuli for proliferation. In the case of Th1-cloned T cells, CD28 signaling costimulates production of autocrine interleukin 2 (IL-2). Th2 cells produce their autocrine growth factor, IL-4, without costimulation, but require APC-derived costimuli, or IL-1, to respond to IL-4. Here we demonstrate that engagement of CD28 on Th2 cells with anti-CD28 antibody or with APC-associated B7 costimulates Th2 responsiveness to IL-4 but does not affect IL-4 or IL-2 production by Th2 cells. Costimulation of Th2 cells via CD28 appears to involve the induction of IL-1 production by Th2 cells, which acts in an autocrine fashion to induce IL-4 responsiveness. These results suggest that CD28-induced costimulation plays an important role in responses mediated by both types of Th cells.

Animals↗
PubMed1993

The role of viral enhancer "core" motif-related sequences in regulating T cell receptor-gamma and -delta gene expression.

T cells express clonally distributed alpha beta or gamma delta Ag receptor heterodimers. Transcriptional enhancers for the genes of all four subunits are active in both gamma delta and alpha beta T cells, but are less active or inactive in other cells. Conserved sequence motifs are present in all four enhancers, suggesting that common transcription factors regulate TCR gene expression. One of these motifs in the gamma 3 site of the TCR-gamma enhancer is similar to motifs found in several other lymphoid-specific and viral enhancers. This conserved "core" sequence is present in the enhancers of Moloney and SL3-3 murine leukemia viruses, important for transcription in T cells and in determining disease specificity. Here we characterize the gamma 3 site of the gamma enhancer and a corresponding homologous site, delta E3, of the TCR-delta enhancer. Our results suggest that the core site is critical for activity of the 200-bp gamma enhancer fragment and of the gamma 3 and delta E3 sites. Furthermore, we identify a nuclear factor in human T cell lines that specifically binds the core region in these and several other core-containing enhancers. This factor may be identical to or related to a purified bovine nuclear core binding factor that binds the core region of the Moloney murine leukemia virus enhancer, gamma 3 and delta E3 sites, suggesting that similar proteins regulate the TCR-gamma, delta and Moloney murine leukemia virus enhancers. Other sequences in the gamma 3 site upstream of the core sequence are also critical for activity in T cells, suggesting that at least two different factors are required for functional activity of the gamma 3 site.

Animals↗
PubMed1993

Selection is not required to produce invariant T-cell receptor gamma-gene junctional sequences.

Recombination of V-, D- and J-gene segments can generate an enormous diversity of T-cell antigen receptor (TCR) gene sequences. Although many gamma delta T cells fully exploit this diversification process, those in the epidermal and vaginal epithelium do not, predominantly expressing invariant gamma delta receptors in which the V-(D)-J junctional sequences in almost all the productive rearrangements are identical. The almost exclusive use of identical TCRs by cells in these sites is thought to reflect recognition of a stress-induced autologous antigen. To explain the prevalence of the invariant junctional sequences, it has been proposed that thymic selection operates on a population of originally diverse progenitor cells, resulting in a homogeneous repertoire. Alternatively the invariant sequences may result from biases in the recombination machinery in the fetal thymic progenitors of these cells. We report here the use of mice into which mutated TCR gamma-gene rearrangement substrates have been introduced as transgenes to demonstrate directly that the canonical TCR V gamma 3-J gamma 1 and V gamma 4-J gamma 1 sequences occur at high frequency in the absence of the possibility of selection for the protein products.

Animals↗