Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.4 (trypsin)
42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mouse and rat myeloma cell lines showed little or no rosette formation with sheep erythrocytes (SRBC) coated with rabbit IgG (rabbit EA) but showed marked rosette formation after treatment with trypsin, pronase or neuraminidase. These cell lines showed no rosette formation with SRBC coated with mouse IgG (mouse EA): treatment with trypsin enabled the detection of rosettes among the mouse myeloma cell lines but not by the rat myeloma cells. The F(ab')2 fragment of the anti-Fc receptor II antibody blocked the formation of rosettes with rabbit EA by mouse myeloma cell lines after treatment with trypsin. Aggregated mouse IgG1 and IgG2b subclasses strongly inhibited the formation of rosettes with rabbit EA, whereas aggregated mouse IgG2a showed a marginal inhibitory effect. A large amount of mouse IgG2a, however, caused significant inhibition. Our results also revealed that aggregated mouse IgG could bind to the rat myeloma cell line. The Fc rosette forming abilities of the enzyme-treated mouse and rat myeloma cells became reduced after cultivation both in the presence and absence of FCS but not after cultivation in the presence of cycloheximide, suggesting that cell surface substances, which may be glycoprotein that incompletely mask Fc receptors, are produced by myeloma cells.
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PMID:Studies on the Fc receptors and masking substances on mouse and rat myeloma cells. 297 95

Antibody-dependent cell-mediated cytotoxicity (ADCC) is a cytolytic mechanism whereby unimmunized lymphoid cells lyse antibody-sensitized target cells. The cells mediating ADCC are referred to functionally as killer cells (K cells). K cells are a heterogeneous population of lymphocytes based on cell membrane marker criteria but may be morphologically homogeneous. It is well established that K cells must have an Fc receptor (FcR) appropriate for the class of target cell-bound antibody, and that physical interaction between the K cell's FcR and the Fc portion of target cell-bound antibody is required for the initiation of lysis. Relatively little is known about the regulatory mechanisms presumed to exist and modulate ADCC reactions. We have made 2 observations that led us to investigate the possibility that the sheep erythrocyte (SRBC) receptor (ER) on human cells might be involved as a regulator of ADCC. First, SRBC are more efficiently lysed by human lymphocytes than are other erythrocyte target cells, and second, although nonsensitized bystander cells are usually not lysed during ADCC reactions, SRBC are consistently lysed. Removal of E-rosetting capacity of lymphocytes by trypsin treatment selectively decreases lysis of IgG sensitized SRBC. Furthermore, lysis of nonsensitized bystander SRBC is also inhibited by trypsin treatment of effector cells. ADCC is also decreased by blocking the ER with simple sugars or monoclonal antibody so that E-rosettes are inhibited. In contrast to trypsin treatment, which selectively inhibits lysis of SRBC, ER-specific monoclonal antibody and simple sugars decrease cytolysis against all target cells tested.
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PMID:Antibody-dependent cell-mediated cytotoxicity by human lymphocytes: a regulatory role for the sheep red blood cell receptor. 299 10

Platelets are one of several cell types capable of mediating antibody-dependent cellular cytotoxicity. We have developed a plasma-free system in which washed mouse platelets lyse washed antibody and complement-sensitized SRBC targets in the presence of EDTA. The dose-response curve is concave to the abscissa, indicating that lysis is a one-hit reaction. Determination of the actual number of platelets required to lyse a target shows that each platelet could lyse a single target. A limited degree of lysis is observed when platelets are incubated with SRBC sensitized with monoclonal IgG2a alone, but no lysis occurs with SRBC bearing comparable amounts of other isotypes. In the presence of C1 through C3, but not C1 through C2, efficient lysis is triggered by complement-fixing monoclonal IgG2a, IgG2b, and IgG3. In contrast, IgM and non-complement-fixing IgG1 and IgE are inactive. To achieve efficient lysis, it appears that platelets require both target cell-bound antibody and C3 fragments in close proximity. It is unlikely that proteases, pore-forming proteins, or toxic oxygen metabolites are involved in platelet-mediated lysis. Freezing and thawing of platelets, sonication, or sonication followed by hypotonic shock causes severe depletion of cytoplasmic and granular contents, as shown by electron microscopy and marker assays. However, the membrane fraction of these preparations retains cytolytic activity. When platelets are treated with trypsin or heated, lytic activity is eliminated, indicating that at least one component of this system is protein. These findings, as well as the fact that platelets do not lyse unsensitized innocent bystander SRBC, suggest that the complete cytotoxic system of platelets capable of specific recognition and lysis resides in their membranes.
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PMID:Platelet-mediated cytotoxicity. Role of antibody and C3, and localization of the cytotoxic system in membranes. 359 64

The 202,000 MW protein XC, which is distinct from C3 but is essential for antibody-dependent haemolytic activity against SRBC, was obtained from Xenopus plasma following polyethylene glycol precipitation, ion-exchange chromatography and gel-filtration. The protein required other components of the Xenopus serum in order to lyse sensitized SRBC, but did not lyse unsensitized RRBC through the alternative pathway. The protein, contained at 0.17 mg/ml in the original plasma, comprised three distinct subunits of 96,000, 76,000 and 26,000, which were linked by disulphide bonds. Digestion by trypsin resulted in a specific cleavage of the 96,000 subunit and a conversion of its immunoelectrophoretic mobility to the anodal side, leaving the 76,000 and 26,000 subunits intact. The treatment with SDS and urea resulted in the splitting of the 96,000 subunits into 48,000 and 45,000 components, but this splitting was inhibited upon pretreatment with methylamine, suggesting the presence of a thiol ester bond in the 96,000 subunit. The amino acid composition of the XC revealed a striking resemblance to that of human C3 and C4. We therefore conclude that the 202,000 protein isolated in this study represents the C4 which plays an essential role in the classical haemolytic pathway.
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PMID:Characterization of the fourth component of complement in the serum of the clawed frog Xenopus laevis. 407 3

Studies were made on the immunoregulatory activity of a lymphokine produced by a B cell clone that does not express immunoglobulin heavy or light chains. The B factor (BEF; B cell-derived enhancing factor), was effective in augmenting the primary and the anamnestic response to SRBC and/or in prolonging the IgG anamnestic response to SRBC and the response to DNP-LE, provided it was added at early stages of culture. The BEF seems to act mainly by preventing the activation of T suppressor cells rather than by counteracting the activity of already activated suppressor cells. Indeed, thymocytes and virgin T cells, but not Con A-activated thymocytes, Con A-activated T cells or B cells, express acceptors for the BEF. The biochemical properties of the BEF were also reported. The apparent m.w. of the factor was 450,000 to 500,000 by gel chromatography. The BEF was sensitive to digestion by papain, trypsin, and subtilisin, indicating that it was protein in nature. The regulatory activity was precipitated by 50% (NH4)2SO4 and was destroyed by heating at 70 degrees C for 30 min or by exposure to pH 2.2 for 6 hr.
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PMID:Regulatory function of Thy-1- cells. IV. Biologic and Biochemical characterization of B cell clone-derived lymphokine (BEF). 622 56

The binding of nascent human C3b (i.e. the fragment of C3 just after trypsin cleavage) to mouse peritoneal macrophages was demonstrated by immune adherence. Acceptor-bound C3b could be detected longer than 24 h on the cell membrane. The rosette formation and phagocytosis of SRBC coated with anti-SRBC rat IgG was inhibited by preincubation of the cells with C3 and trypsin (15 min, 37 degrees C). However, the phagocytosis of opsonized yeast particles was not influenced by acceptor-bound C3b, proving that C3b-C3b acceptor interaction did not alter the function of C3b-receptors. Acceptor-bound C3b on the macrophages failed to mediate phagocytosis of human 0,Rh+ red cells having C3b-receptors.
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PMID:C3b acceptors on macrophages: inhibition of Fc gamma-receptor-mediated phagocytosis by acceptor-bound C3b. 622

Addition of intact erythrocytes to semisolid agar cultures of murine B cells dramatically improves cloning efficiency and affects colony morphology. In this study, we investigated possible mechanisms through which this might occur. Specific modification of sheep erythrocyte (SRBC) membranes by treatment with trypsin but not other enzymes improved colony potentiation and erythrocytes from rats, mice, and humans were also effective after trypsin treatment. In addition, autoantibody-coated murine erythrocytes were superior to normal cells in this regard. These observations suggest that erythrocytes enhance lymphocyte survival and/or proliferation by means of particular membrane-mediated processes. The possible importance of erythrocytes as scavengers of toxic hydroxyl radicals was also investigated. Deliberately generated radicals formed by addition of dihydroxyfumaric acid and iron were effectively countered by addition of SRBC. More detailed analyses revealed that of several endogenously produced toxic species, hydrogen peroxide may be the most important under ordinary culture conditions. That is, addition of catalase but not superoxide dismutase or mannitol improved cloning efficiency in cultures lacking SRBC. These studies suggest that erythrocytes have a beneficial effect on lymphocyte survival and function in culture through at least two mechanisms.
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PMID:Analysis of the effects of erythrocytes on mitogen-dependent clonal proliferation of murine B lymphocytes. 660 24

The hemolytic activity against SRBC in the serum of normal Xenopus is dependent on specific antibody and both Ca++ and Mg++, whereas the activity against RRBC is dependent on Mg++ alone. Both of these hemolytic activities disappeared after treatment of the serum with zymosan or with the specific rabbit antiserum against one of the zymosan-binding proteins in Xenopus serum. By using this antiserum as a probe, a complement component (XC) was purified as a single entity from the Xenopus plasma after polyethylene glycol precipitation, DEAE-Sepharose CL-6B, Sepharose CL-6B, and Sephadex G-200 column chromatographies. The XC, contained at 2.3 mg/ml in normal serum, showed an electrophoretic mobility of beta-globulin, with a m.w. of 204,000 (204K) comprising two distinct subunits of 125K and 85K, which are linked with each other by disulfide bonds. The 204K protein exhibited a strong hemolytic activity in association with other components in Xenopus serum. Digestion of 204K protein by trypsin resulted in a specific cleavage of the 125K subunit and a conversion of its immunoelectrophoretic mobility to the anodal side, leaving the 85K subunits intact. The treatment of XC with SDS and urea resulted in the splitting of 125K subunits into 78K and 40K, but this splitting was inhibited upon pretreatment with methylamine, suggesting the presence of a thiol ester bond in the XC. The amino acid composition of the XC revealed a striking resemblance to that of mammalian C3. In all aspects, the 204K protein (XC) is regarded as representing the C3 of Xenopus laevis, which plays a key role in both the classical and alternative hemolytic pathways.
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PMID:Isolation and characterization of the third component of complement in the serum of the clawed frog, Xenopus laevis. 674 92

Mice infected with Plasmodium berghei have a depressed immune response to a variety of antigens. We report the extraction, purification, and characterization of a soluble immunosuppressive substance derived from P. berghei-infected mouse blood. A crude extract, prepared by solubilization of infected erythrocytes in a Parr cell disruption bomb, reduced the anti-DNP PFC response of mice injected with the extract 1 day before immunization. Purification of the immunosuppressant was accomplished by precipitation with 50% saturated ammonium sulfate followed by chromatography on Sephadex G-150 in the presence of 6 M guanidine hydrochloride. The immunosuppressive activity was recovered in the last fraction eluted from the Sephadex G-150 column that contained low m.w. components. The activity was abrogated by trypsin digestion, but not by periodate oxidation. Volume for volume, the purified immunosuppressant had a 100-fold greater activity than the crude extract from which it was derived. It suppressed the response to the T-dependent antigens DNP-KLH and SRBC, but not to the T-independent antigen DNP-Ficoll.
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PMID:Immunosuppression in murine malaria: a soluble immunosuppressive factor derived from Plasmodium berghei-infected blood. 702 64

Members of the Trypanosomatidae were studied for their ability to acquire host IgG through a possible Fc receptor. A simple rosette test was devised in which the different species and forms of protozoa were mixed with SRBC sensitized with subagglutinating does of IgG, IgM, and F (ab') 2 anti-SRBC, and the pelleted mixture was observed for the number of clumps (rosettes) formed between the parasites and SRBC. Rosettes were formed between parasites and SRBC sensitized with IgG but not with IgM or F(ab')2, indicating the presence of a receptor for IgG Fc. The specificity of this receptor for Fc was confirmed by inhibition experiments with normal rabbit aggregated gammaglobulins or with purified normal rabbit Fc. The receptor is sensitive to treatment with trypsin but regenerates after a short period of incubation (1 h), which indicates that it is synthesized by the parasite itself. Interesting was the observation that only pathogenic members of the Trypanosomatidae formed rosettes with sensitized SRBC. In none of the nonpathogenic forms studied could we demonstrate the Fc receptor. Also important was the finding that freshly isolated blood stream forms of Trypanosoma cruzi from infected mice did not form rosettes. However, after trypsinization, these forms clearly displayed the ability to do so, possibly indicating a previous acquisition of the host IgG by the parasites in the mouse blood stream. These findings point to a possible and important means of parasite evasion of the host immune response by masking their surface with host IgG.
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PMID:Receptor for immunoglobulin Fc on pathogenic but not on nonpathogenic protozoa of the Trypanosomatidae. 703 34


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