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)

Cyclosporine (CsA) was tested for its ability to inhibit antigen presentation by spleen cells or the B lymphoma line A20 to T cell hybridomas specific for hen egg-white lysozyme (HEL). Antigen-presenting cells (APC) were treated with CsA or nonimmunosuppressive derivatives thereof during or prior to encounter with antigen. The APC were then washed extensively and incubated in CsA-free medium for 6 hr before the T hybridoma cells were added. Under these conditions, CsA had no effect on antigen presentation up to the cytostatic regimen (1 microgram/ml). Omission of the 6-hr interval between CsA treatment of APC and the addition of T hybridoma resulted in inhibition of interleukin 2 production, although the CsA concentrations required were 10-75-fold higher than the ones inhibiting T cells directly (IC50: 100-150 ng/ml vs. 2-10 ng/ml). The responses to both HEL and a synthetic peptide of HEL sequence 105-120 were inhibited, indicating that the step influenced by the drug was not antigen-processing. The nonimmunosuppressive derivatives remained ineffective under these conditions. The results illustrate that the carryover of CsA from APC to T cells can mimic a drug effect on antigen presentation. Therefore, the demonstration of a CsA effect on antigen presentation can only be considered as conclusive when the readout of APC function is not a T cell response.
 ...
PMID:Lack of influence of cyclosporine on antigen presentation to lysozyme-specific T cell hybridomas. 326 67

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.
 ...
PMID:Cell type-specific processing of the I-Ed-restricted hen egg lysozyme determinant 107-116. 876 76

Conformational stability of proteins is an important factor that determines their resistance/susceptibility to proteolytic digestion. Intracellular proteolysis is the key step in antigen presentation events for protein antigens; hence, it is likely that increasing protein stability reduces the antigenicity of proteins. We prepared three hen egg white lysozyme derivatives possessing different stabilities by chemical modification to clarify the relationship between conformational stability and the antigenicity of the protein. One of the derivatives was conformationally unstabilized by removing one intramolecular disulfide bond, whereas the two others were stabilized by the addition of an intramolecular cross-link. The antigenicity of these derivatives was evaluated using hen egg white lysozyme-specific T-cell hybridoma cells and a B-lymphoma cell line, A20, as antigen-presenting cells. With an increase in conformational stability, the T-cell response decreased. However, the reduction was not derived from the inefficiency of internalization to A20 cells nor the alteration of antigenicity by chemical modifications. Moreover, from analyses of their susceptibility to proteolysis and the kinetics of presentation of the T-cell epitope, it was confirmed that increasing protein stability led to the depression of T-cell epitope generation by increasing resistance to proteolysis. These results have an important implication in devising a new strategy for manipulating T-cell response by the stability of protein antigen.
 ...
PMID:Depression of T-cell epitope generation by stabilizing hen lysozyme. 940 12

While a sorting signal in the cytoplasmic tail of the major histocompatibility complex (MHC) class II molecules is known to influence their endocytic transport, potential effects of the transmembrane (TM) domain of the MHC class II molecules on endocytic transport remain unclear. We have examined the role of the TM domain by comparing antigen-presenting functions of the wildtype (WT) I-Ab and mutant (MT) I-Ab molecule substituted in the beta-chain TM with alpha chain TM. A20 cells transfected with WT I-Ab were able to present antigen (hen egg lysozyme) better to some hybridomas, while those transfected with MT I-Ab consistently outperformed WT for other hybridomas recognizing different epitopes. This difference in antigen processing and presentation is not caused by the differences in H-2M (DM) requirement or association with Ii. The time required for processing of specific epitopes appears to be different, suggesting sequential involvement of various endocytic compartments in the antigen processing. Although both WT and MT molecules were found in the early endocytic (transferrin receptor-rich) compartments, MT molecules accumulated in these compartments in higher quantities for longer time periods. Similarly, the MT molecule is retained for a longer time period than WT in late endocytic (LAMP-1 associated) compartments. Together, our data indicate an important role of the TM domain of the MHC class II molecules in the intracellular trafficking and, consequently, antigen processing and presentation.
 ...
PMID:Role of the major histocompatibility complex class II transmembrane region in antigen presentation and intracellular trafficking. 1502 1

Immobilized metal-chelate affinity chromatography has been widely used in the purification of proteins, and we have recently found that it can also be applied to purification of nucleic acids through interactions involving exposed bases, especially purines. Here we report that the inclusion of moderate quantities of neutral solutes in the buffer substantially enhances the binding affinity of nucleic acids for immobilized metal-chelate affinity adsorbents. Addition of 20% (v/v) of solutes such as ethanol, methanol, isopropanol, n-propanol, and dimethyl sulfoxide enhances the initial affinity of binding of total yeast RNA by 4.4-, 3.8-, 3.7-, 3.0-, and 2.8-fold, respectively for Cu(II)-iminodiacetic acid (IDA) agarose adsorbent, and the weaker adsorption by Cu(II)-nitrilotriacetic acid (NTA) agarose was even more strongly enhanced. The adsorption affinities of the smaller oligodeoxynucleotide molecules A20, G20, C20 and T20 also increase with the addition of ethanol, suggesting that the effect is not significantly mediated by conformational changes. Binding enhancement generally correlates with reduction of water activity by the various solutes, as predicted by several models of solution thermodynamics, consistent with an entropic contribution by displacement of waters from the metal-chelate. Interestingly, the enhancement was not seen with the proteins bovine serum albumin and lysozyme.
 ...
PMID:Neutral additives enhance the metal-chelate affinity adsorption of nucleic acids: role of water activity. 1660 Feb 63

Nitric oxide has been shown to induce immunosuppression by inhibiting class II MHC molecule expression and T-lymphocyte proliferation. However, much less is known about the ability of NO to interfere with antigen processing and presentation. So we questioned whether B lymphoma cells exposed to NO could be impaired in their ability to process lysozyme and to stimulate proliferation of a syngeneic T-cell hybridoma. As immunosuppressive pathological conditions are often associated with a pro-oxidative milieu, we also examined the influence of intracellular GSH levels on NO responsiveness. Exposure of GSH-depleted B cells to NO-releasing compounds lowered their capacity to present a reduced and alkylated lysozyme (TAP-HEL), although presentation of a lysozyme-derived peptide was unaffected. Cells with a normal GSH content were protected from this inhibition. Fluid phase endocytosis, protein synthesis and expression of class II molecules remained normal in GSH-depleted cells. However, proteolysis of a dye conjugate of ovalbumin was strongly inhibited, suggesting that protease inhibition might be involved. Cathepsin B activity, which was necessary to TAP-HEL processing, was inhibited by the NO-donors. The inhibition was higher in GSH-depleted cells and reproduced by treatment of A20 B cells by two cathepsin inhibitors. These results show that, in addition to cytostasis and reduction in class II expression, NO-induced immunosuppression could also implicate inhibition of antigen processing under oxidative stress conditions.
 ...
PMID:Glutathione depletion reveals impairment of antigen processing and inhibition of cathepsin activity by nitric oxide in antigen-presenting cells. 1909 6