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

B-cell tolerance to soluble protein self antigens such as hen egg lysozyme (HEL) is mediated by clonal anergy. Anergic B cells fail to mount antibody responses even in the presence of carrier-primed T cells, suggesting an inability to activate or respond to T helper cells. To investigate the nature of this defect, B cells from tolerant HEL/anti-HEL double-transgenic mice were incubated with a membrane preparation from activated T-cell clones expressing the CD40 ligand. These membranes, together with interleukin 4 and 5 deliver the downstream antigen-independent CD40-dependent B-cell-activating signals required for productive T-B collaboration. Anergic B cells responded to this stimulus by proliferating and secreting antibody at levels comparable to or better than control B cells. Furthermore, anergic B cells presented HEL acquired in vivo and could present the unrelated antigen, conalbumin, targeted for processing via surface IgD. In contrast, the low immunoglobulin receptor levels on anergic B cells were associated with reduced de novo presentation of HEL and a failure to upregulate costimulatory ligands for CD28. These defects in immunoglobulin-receptor-mediated functions could be overcome in vivo, suggesting a number of mechanisms for induction of autoantibody responses.
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PMID:Anergic self-reactive B cells present self antigen and respond normally to CD40-dependent T-cell signals but are defective in antigen-receptor-mediated functions. 751 4

Expression of CD68 (macrosialin) in the absence of surface and lysosomal lineage marker molecules is a characteristic feature of T zone-associated plasmacytoid monocytes, which were recently shown to represent precursors of dendritic cells (DC). We demonstrate here a minor population of strongly CD68-positive (CD68bright) blood cells that lack all analyzed myeloid surface (CD14-, CD33-, CD13-, CD11b-, CD11c-) and lysosomal (myeloperoxidase, MPO- and lysozyme, LZ-) marker molecules (0.4 +/- 2% of the total mononuclear cells). These CD68bright, lineage marker-negative (lin-) cells can be induced to proliferate in the presence of IL-3. They do not acquire myeloid features even upon stimulation with granulocyte-macrophage CSF plus IL-1, IL-3, and IL-6. Instead, these cells develop typical DC characteristics upon culture. Furthermore, these CD68brightlin- DC precursors acquire mature DC characteristics (CD86+, CD83+, CD54bright) upon stimulation with CD40 ligand plus IL-3. A second subset of DC precursor-like blood cells was found to weakly express CD68 (0.3 +/- 0.2% of the total mononuclear cells) and to coexpress several myeloid lineage associated molecules (LZ+, CD11c+, CD33+, CD13+). Cells of this second subset resemble both previously described myeloid-related peripheral blood DC and germinal center DC. Analysis of peripheral blood leukocytes for CD68 thus revealed the existence of two cell subsets that phenotypically resemble lymphoid tissue-associated DC. The unique phenotype CD68brightlin- is highly reminiscent of T zone-associated plasmacytoid monocytes. CD68brightlin- blood leukocytes also functionally resemble plasmacytoid monocytes. The lack of all analyzed myeloid features by CD68brightlin- blood leukocytes suggests that these cells arise from a novel nonmyeloid human DC differentiation pathway.
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PMID:Identification of CD68+lin- peripheral blood cells with dendritic precursor characteristics. 967 Sep 50

Many antigens encountered by the immune system are included in complex structures such as bacteria or parasites. We previously developed an in vivo model to study the immunogenicity of particulate antigens, based on covalent linkage of proteins or peptides to 1 microm latex particles and showed that these antigens cannot be presented to MHC class II-restricted specific T cells by B cells. However, they induce strong CD4+ T cell responses when injected to mice without adjuvant. The present study demonstrates that four out of the five proteins tested did not stimulate antibody synthesis when linked to 1 microm microparticles, although a strong IgG production was induced by the same proteins administered in soluble form with adjuvant. In contrast, lysozyme and two synthetic peptides containing B and T cell viral epitopes induced strong and long-lasting specific antibody responses when linked to 1 micrometer synthetic beads. The isotypic pattern of antibodies induced by particulate lysozyme was similar to that induced by the soluble protein in alum. Studies using CD4+ T cell-depleted mice revealed that the induction of antibodies by particulate lysozyme strictly required Th cell activity. Moreover, the T-B cell cooperation involved in B cell activation by antigens linked to beads required CD40-CD40 ligand interaction. Thus, these particulate antigens provide a useful tool to study the mechanisms of induction of antibody response against complex bacterial or parasitic antigens. Moreover, they may represent attractive candidates to elaborate efficient new vaccines using short synthetic peptides.
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PMID:Activation of B cells by 1 microm particulate lysozyme or peptides: a Th-dependent pathway requiring CD40-CD40 ligand interaction. 972 97

During their final differentiation or maturation, dendritic cells (DCs) redistribute their major histocompatibility complex (MHC) class II products from intracellular compartments to the plasma membrane. Using cells arrested in the immature state, we now find that DCs also regulate the initial intracellular formation of immunogenic MHC class II-peptide complexes. Immature DCs internalize the protein antigen, hen egg lysozyme (HEL), into late endosomes and lysosomes rich in MHC class II molecules. There, despite extensive colocalization of HEL protein and MHC class II products, MHC class II-peptide complexes do not form unless the DCs are exposed to inflammatory mediators such as tumor necrosis factor alpha, CD40 ligand, or lipoplolysaccharide. The control of T cell receptor (TCR) ligand formation was observed using the C4H3 monoclonal antibody to detect MHC class II-HEL peptide complexes by flow cytometry and confocal microscopy, and with HEL-specific 3A9 transgenic T cells to detect downregulation of the TCR upon MHC-peptide encounter. Even the binding of preprocessed HEL peptide to MHC class II is blocked in immature DCs, including the formation of C4H3 epitope in MHC class II compartments, suggesting an arrest to antigen presentation at the peptide-loading step, rather than an enhanced degradation of MHC class II-peptide complexes at the cell surface, as described in previous work. Therefore, the capacity of late endosomes and lysosomes to produce MHC class II-peptide complexes can be strictly controlled during DC differentiation, helping to coordinate antigen acquisition and inflammatory stimuli with formation of TCR ligands. The increased ability of maturing DCs to load MHC class II molecules with antigenic cargo contributes to the >100-fold enhancement of the subsequent primary immune response observed when immature and mature DCs are compared as immune adjuvants in culture and in mice.
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PMID:The formation of immunogenic major histocompatibility complex class II-peptide ligands in lysosomal compartments of dendritic cells is regulated by inflammatory stimuli. 1072 55

We examined the frequencies and specificities of the CD4+ T cell responses to the protein hen egg white lysozyme in mice deficient in the CD40-CD40 ligand or B7-CD28 costimulatory pathways. The frequency of T cells was decreased by between 3- and 4-fold in CD40-/- mice, and 12-fold in B7-1/B7-2-/- mice, but surprisingly, the relative distribution of T cells responding to peptides that were presented at levels that differed by >250-fold was similar. We also examined the CD4 response after blocking the regulatory molecule CTLA-4 during immunization. We observed no difference in either the frequency or specificity of the CD4+ T cell response if CTLA-4 was blocking during priming. Thus, the T cell response was generated toward the constellation of chemically dominant and subdominant epitopes as a whole, and did not discriminate among them based on their relative abundance.
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PMID:Cutting edge: the relative distribution of T cells responding to chemically dominant or minor epitopes of lysozyme is not affected by CD40-CD40 ligand and B7-CD28-CTLA-4 costimulatory pathways. 1221 93