Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.17 (lysozyme)
 21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The invariant chain (Ii) binds to newly synthesized major histocompatibility complex (MHC) class II molecules and is targeted to an acidic compartment where it is degraded. To evaluate its role on the conformation and the subcellular distribution of murine MHC class II molecules we have established stable L cell transfectants expressing class II IAk heterodimers alone or in conjunction with p31 and p41 Ii chains. In these cells, class II molecules were present under three forms: alpha beta heterodimers bearing high mannose carbohydrate moieties, and fully glycosylated alpha beta heterodimers that are sensitive or resistant to sodium dodecyl sulfate dissociation at 20 degrees C. The latter class II molecules called compact heterodimers, were here highly induced in Ii-positive cells. Using in situ iodination of endosomal compartments, class II heterodimers were detected in late endosomal compartments essentially as compact forms in Ii-positive cells, and as non-compact forms in Ii-negative cells. Using confocal microscopy, IAk molecules were located in compartments distinct from early endosomes labeled with transferrin, but partially coincident with vesicles containing fluid-phase markers, and highly coincident with compartments containing large amounts of cathepsins B, D, H, and L in Ii-positive and Ii-negative cells. At the ultrastructural level, class II molecules were mostly present in multivesicular bodies, even without Ii expression. But Ii chains were needed to induce an efficient presentation of the hen egg lysozyme antigen and were sufficient to promote a major conformational change of the late endosomal, and/or lysosomal resident, class II molecules. Ii molecules are presumably playing a chaperoning function favoring the association of peptides with class II molecules in endosomal compartments.
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PMID:The invariant chain induces compact forms of class II molecules localized in late endosomal compartments. 825 30

We have tested the involvement of the invariant chains (Ii) p31 and p41 in the presentation of peptides derived from hen egg lysozyme (HEL) constructs targeted to different intracellular compartments within transfected fibroblasts. The endogenous HEL constructs were either present in the cytosol (HELc), secreted (HELs), or linked to the mammalian (KDEL C-terminal sequence that causes retention of HEL in the endoplasmic reticulum (ER)/pre-Golgi recycling compartment (HELr). Using Ii-negative antigen-presenting cells, the presentation of HELr to a HEL 46-61 specific T cell hybridoma was far less efficient than the presentation of the HELs. High levels of Ii expression enhanced drastically the presentation of the HEL 46-61 determinant derived from both HELr and HELs. HELr and HELs presentation was fully sensitive to lysosomotropic agents such as chloroquine, indicating that the formation of complexes between major histocompatibility complex (MHC) class II molecules and determinants derived from endogenous antigens entering the secretory pathway is taking place in an acidic compartment. The degradation and dissociation of Ii might be a prerequisite for the efficient presentation of endogenously derived determinants by MHC class II molecules, as for the presentation of most exogenous antigens. All our results are compatible with the notion that endogenous molecules being translocated into the lumen of the ER could be presented by class II molecules through a processing pathway involving an acidic compartment in which Ii chains dissociate from class II molecules.
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PMID:Major histocompatibility complex class II-restricted presentation of secreted and endoplasmic reticulum resident antigens requires the invariant chains and is sensitive to lysosomotropic agents. 825 31

We have examined the interactions of various peptides with the mouse class II major histocompatibility complex molecule I-Ak. The peptides were derived from the model protein hen egg white lysozyme (HEL). The immunodominant peptide of HEL is a 10-mer, residues 52-61. Our previous work established that this sequence contains the key residues for binding and presentation to T cells. Now we show that the binding of this 10-mer sequence resulted in complexes of I-Ak and peptide that, in SDS/PAGE (without boiling the protein), rapidly dissociated from the component alpha and beta chains. The binding interactions were studied in vitro, by incubating purified I-Ak and radiolabeled peptide, or ex vivo, by using antigen-presenting cells incubated with peptides. Peptides with additional residues at either the amino or carboxyl terminus behaved dramatically differently. Complexes of I-Ak with the longer peptides were stable to SDS/PAGE. Very few amino acid additions result in the change from unstable to stable complexes. The important issue here is that when cultured with HEL, antigen-presenting cells selected the HEL peptides containing the 52-61 sequences that favored stability [Nelson, C. A., Roof, R. W., McCourt, D. W. & Unanue, E. R. (1992) Proc. Natl., Acad. Sci. USA 89, 7380-7383]. Also, from other studies, such sequences correlate with a high immunogenicity of the peptide. We conclude that there are structural features of peptides that change the stability of the class II molecule and that are independent of the "core" peptide seen by the T cells.
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PMID:Identification of two distinct properties of class II major histocompatibility complex-associated peptides. 843 83

The self-mouse lysozyme peptide corresponding to residues 46-62 (ML46-62) binds to the major histocompatibility complex (MHC) class II molecules I-A(k) and it selectively inhibits, when coinjected with antigen, priming of I-A(k)-restricted, antigen-specific T cells. We demonstrate that administration of ML46-62 also inhibits in vivo antibody responses induced by I-A(k)-restricted T helper cells. ML46-62 is able to prevent the primary anti-hen egg white lysozyme (HEL) antibody response induced by the entire HEL molecule in B10.A(4R) mice, expressing only I-A(k) molecules, but not in mice of H-2d haplotype. ML46-62 also strongly decreases, in B10.A(4R) mice, the antibody response to ribonuclease A, a protein antigen unrelated to the MHC blocker, indicating that MHC blockade is the mechanism leading to inhibition of antibody response. This is further supported by the concomitant decrease, in vivo, of complex formation between immunodominant HEL peptides and I-A(k) molecules, preventing I-A(k)-restricted T cell induction. Administration of ML46-62 after antigen priming does not affect ongoing antibody responses, as expected from MHC blockade. A single injection of ML46-62 at the time of protein antigen priming precludes not only the primary, but also the secondary antibody response to a subsequent challenge with soluble protein, even when the challenge is performed several months after priming. Coinjection of antigen and MHC antagonist inhibits production of all antibody isotypes equally well, suggesting that MHC class II blockade affects both Th1- and Th2-type T helper cells. Therefore, these results indicate that administration of MHC class II-binding peptides can efficiently and selectively prevent the induction of T cell-dependent primary and secondary in vivo antibody responses by blocking antigen presentation to class II-restricted T helper cells.
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PMID:Selective immunosuppression by administration of major histocompatibility complex class II-binding peptides. II. Preventive inhibition of primary and secondary in vivo antibody responses. 847 15

A self-peptide containing amino acid residues 46-61 (NRGDQSTDYGIFQINSR) of mouse lysozyme (ML) (p46-61, which binds strongly to the A(k) molecule but does not bind to the E(k) molecule), can induce a strong proliferative T cell response in CBA/J mice (A[k], E[k]) but no response at all in B10.A(4R) and CBA/J mice. The critical residues within p46-59 are immunogenic in both B10.A(4R) and CBA/J mice. The critical residues within p46-61 reside between amino acid positions 51 and 59. T cells of B10.A(4R) mice primed with the truncated peptides in vivo cannot be restimulated by p46-61 in vitro. This suggests that T cell receptor (TCR) contact (epitopic) residue(s) flanking the minimal 51-59 determinant within p46-61 hinder the interaction of the p46-61/A(k) complex with the appropriate TCR(S), thereby causing a lack of proliferative T cell response in this mouse strain. Unlike B10.A(4R) mice, [B10.A(4R) x CBA/J]F1 mice responded vigorously to p46-61, suggesting that thymic APC of B10.A(4R) mice do not present a self ligand to T cells resulting in a p46-61-specific hole in the T cell repertoire in B10.A(4R) or the F1 mice. Moreover, APC from B10.A(4R) mice are capable of efficiently presenting p46-61 to peptide-specific T cell lines from CBA/J mice. The proliferative unresponsiveness of B10.A(4R) mice to p46-61 is not due to non-major histocompatibility complex genes because B10.A mice (A[k], E[k]) respond well to p46-61. Interestingly, B10.A(4R) mice can raise a good proliferative response to p46-61 (R61A) (in which the arginine residue at position 61 (R61L/F/N/K), indicating that R61 was indeed responsible for hindering the interaction of p46-61 with the appropriate TCR. Finally, chimeric mice [B10.A(4R)-->B10.A] responded vigorously to p46-61, suggesting that thymic antigen presentation environment of the B10.A mouse was critical for development of a p46-61-reactive T cell repertoire. Thus, we provide experimental demonstration of a novel mechanism for unresponsiveness to a self peptide, p46-61, in the B10.A(4R) mouse owing to hindrance: in this system it is the interaction between the available TCR and the A(k)/p46-61 complex, which is hindered by epitopic residue(s) within p46-61. We argue that besides possessing T cells that are hindered by R61 of p46-61, CBA/J and B10.A mice have developed an additional subset of T cells bearing TCRs which are not hinderable by R61, presumably through positive selection with peptides derived from class II E(k), or class I D(k)/D(d) molecules. These results have important implications in self tolerance, shaping of the T cell repertoire, and in defining susceptibility to autoimmunity.
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PMID:Unresponsiveness to a self-peptide of mouse lysozyme owing to hindrance of T cell receptor-major histocompatibility complex/peptide interaction caused by flanking epitopic residues. 862 65

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.
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PMID:The two membrane proximal domains of CD4 interact with the T cell receptor. 864 20

Self-reactive B cells from tolerant double-transgenic (Dbl-Tg) mice coexpressing hen egg lysozyme (HEL) and rearranged anti-HEL immunoglobulin genes have a relatively short life span when compared to normal B cells, irrespective of whether they are exposed to antigen in multivalent membrane-bound form (mHEL-Dbl-Tg mice) or soluble form (sHEL-Dbl-Tg mice). The factors responsible for determining the fate of these B cells after encounter with self-antigen were investigated using a cell-tracking technique in which anti-HEL Ig-Tg spleen cells were labeled with the intracellular dye 5-carboxyfluorescein diacetate-succinimidyl ester (CFSE) and injected either into non-Tg recipients or a variety of HEL-Tg hosts. In non-Tg recipients, HEL-binding B cells persisted in the circulation and could be detected in the follicles of the spleen for at least 5 d. On transfer into either mHEL-Tg or sHEL-Tg hosts, they underwent activation and then rapidly disappeared from the blood and spleen over the next 3 d, consistent with the short life span reported previously. Immunohistology of spleens from sHEL-Tg recipients indicated that the transferred B cells had migrated to the outer margins of the periarteriolar lymphoid sheath (PALS), where they were detectable for 24 h before being lost. The positioning of B cells in the outer PALS depended on a critical threshold of Ig receptor binding corresponding to a serum HEL concentration between 0.5 and 15 ng/ml, but was not restricted to endogenously expressed HEL in that the same migratory pattern was observed after transfer into non-Tg recipients given exogenous (foreign) HEL. Moreover, bone marrow-derived immature Ig-Tg B cells homed to the outer PALS of sHEL-Tg mice and then disappeared at the same rate as mature B cells, indicating that the stage of maturation did not influence the fate of self-reactive B cells in a tolerant environment. On the other hand, HEL-binding B cells transferred into sHEL-Dbl-Tg recipients persisted over the 3-d period of study, apparently due to insufficient availability of antigen, as indicated by the fact that the degree of Ig receptor downregulation on the transferred B cells was much less than in sHEL-Tg recipients. If T cell help was provided to Ig-Tg B cells at the time of transfer into sHEL-Tg recipients in the form of preactivated CD4+ T cells specific for major histocompatibility complex-peptide complexes on the B cell surface, HEL-binding B cells migrated through the outer PALS of the spleen to the follicle, where they formed germinal centers, or to adjacent red pulp, where they formed proliferative foci and secreted significant amounts of anti-HEL antibody. Taken together, these results indicated that the outcome of the interaction between self-antigen and B cells is largely determined by a combination of the degree of receptor engagement and availability of T cell help.
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PMID:The fate of self-reactive B cells depends primarily on the degree of antigen receptor engagement and availability of T cell help. 864 4

We have previously reported that the buccal mucosa can support delayed type hypersensitivity (DTH) reactions to contact sensitizers. In the present study, we show that cells isolated from the buccal epithelium are able to present soluble exogenous antigens to specific T cells. Single cell suspensions obtained by enzymatic dispersion of buccal epithelial sheets could present the native protein antigen hen-egg lysozyme (HEL) to the I-Ak-restricted CD4+ T-cell hybridoma specific for a.a 46-61 on HEL. T-cell activation resulted in interleukin-2 (IL-2) production which could be inhibited by anti-major histocompatibility complex (MHC) class-II antibodies of pertinent specificity. Immunohistochemical staining of whole buccal epithelial sheets revealed that all MHC II positive cells had a dendritic morphology and expressed ATPase activity, indicating that these cells represent a major antigen-presenting cell (APC) population in this tissue. Furthermore, single cell suspensions isolated from buccal epithelium (BEC) after local in vivo administration of either a native soluble protein, a synthetic dodecapeptide, or a contact sensitizer were able to activate antigen-specific T cells ex vivo. Kinetic analyses indicated that maximal APC activity in the oral epithelium occurred within 1 hr after local antigen administration, and had essentially vanished after 24 hr. Conversely, APC activity was undetectable in draining cervico-mandibular lymph node cell suspensions recovered 1 hr after local antigen injection but became manifest after 3-24 hr. These observations suggest that dendritic cells can acquire antigens in the buccal epithelium and migrate to draining lymph nodes where they present processed antigen to MHC class II-restricted T cells. This APC population may thus be a critical element in the initiation of Th1-driven DTH responses in the oral mucosa.
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PMID:Antigen presentation in the murine oral epithelium. 870 42

A high proportion (up to 30%) of major histocompatibility complex (MHC) class II-bound peptides in the mouse and humans contains a proline residue at the N-terminal penultimate position (XP motif). We used a set of ovalbumin (OVA)-specific and hen egg lysozyme (HEL)-specific T cell hybridomas and asked whether the XP motif in MHC class II-associated peptides might influence the stimulation of T cells. We created N-terminally substituted variants of OVA323-339, an H2-Ad restricted OVA epitope and of HEL50-63, a dominant epitope in the context of H2-Ak. Our results show that the N-terminal sequence of MHC class II-bound peptides has a strong impact for the overall stimulation of specific T cells. Proline at the N terminus of antigenic peptides, in contrast to other amino acids, is tolerated or even enhances the recognition of MHC class II-bound peptides significantly.
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PMID:A biological function for the XP motif within the N terminus of major histocompatibility complex class II-associated peptides. 876 27

Class II major histocompatibility complex heterodimers present to T cells determinants as sets of antigen fragments with ragged N and C termini. It is not yet elucidated whether different types of antigen-presenting cells generate identical sets of peptides containing the same determinant. Taking advantage of recombinant I-Ed molecules produced by insect cells as empty heterodimers, a sensitive T cell stimulation assay was developed to analyze naturally processed hen egg lysozyme (HEL) peptides. I-Ed preparations were isolated from antigen-presenting cells cultured with HEL. Following acid treatment, peptides eluted from I-Ed were chromatographed and the fractions incubated at acidic pH with purified recombinant I-Ed molecules, conditions which favor peptide binding. The stimulatory capacity of the reconstituted peptide-I-Ed complexes adsorbed on the well surface of cell culture plates was then evaluated by measuring interleukin-2 secreted by an HEL 107-116-specific, I-Ed-restricted T cell hybridoma. We found that the B lymphoma A20 and an I-Ed-transfected fibroblast cell line generated distinct sets of peptides containing the HEL sequence 107-116. Our results suggest the possibility that presentation of one determinant by different types of antigen-presenting cells stimulates populations of T cells with distinct fine antigen specificities.
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PMID:Cell type-specific processing of the I-Ed-restricted hen egg lysozyme determinant 107-116. 876 76


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