Loss of IgE receptors and shedding of a protease during purification of mast cells

Effect of purification, theophylline and sodium fluoride on histamine release produced by antineoplastic drugs on rat mast cells. A distinctive mechanism of action for carboplatin

The antineoplastic drugs, cytarabine, ifosfamide, vinorelbine, doxorubicin, asparaginase and carboplatin, elicit histamine release from rat pleural and peritoneal mast cells. Both cell populations do not show heterogeneity in their response to stimulation by any of these drugs, with the exception of cytarabine, which activates pleural mast cells at lower concentrations. When these cells are purified with Percoll, L-asparaginase, vinorelbine and cytarabine completely lose their capability of inducing histamine release in both cell populations, while the other drugs still show the same pattern of response as with unpurified cells. These results indicate that some membrane component crucial for the action of vinorelbine, L-asparaginase and cytarabine is lost during the purification procedure. Pretreatment of the cells with theophylline completely inhibits the response to cytarabine, ifosfamide, vinorelbine and asparaginase, and inhibits the response to doxorubicin by up to 75% only. Theophylline does not change the response to carboplatin. Sodium fluoride does not change the response to any of the drugs tested, with the exception of carboplatin, in which case a complete inhibition is observed. In conclusion, carboplatin activates rat mast cells through a completely different mechanism of action with respect to the other drugs studied.

Monoclonal murine anti-DNP IgE: in vitro histamine release of rat mast cells in the presence of reaginic rat and mouse sera

Mast cells from normal rats and animals reinfected with Nippostrongylus brasiliensis (N.b.) were sensitized in vitro with monoclonal anti-DNP mouse IgE, reaginic mouse serum with ovalbumin (OA) specificity and reaginic rat serum against N.b. The sensitized cells were triggered for the release of histamine with DNP-bovine-serum-albumin (DNP-BSA), OA, N.b.-homogenate and guinea-pig anti-mouse IgE. The histamine release from normal mast cells sensitized with monoclonal mouse IgE was inhibited either with N.b.-reaginic rat serum or OA-reaginic mouse IgE (30 micrograms/10(5) mast cells) completely desensitized mast cells from reinfected rats for specific histamine release in the presence of either N.b.-antigen or DNP-BSA. Anti-mouse IgE which was prepared by monoclonal mouse IgE did not bind to rat mast cells sensitized with rat IgE as was revealed by immunofluorescence experiments. Consequently we observed that anti-mouse IgE failed to trigger the histamine release from mast cells of reinfected rats.

A characterization of beta-adrenergic receptors on cellular and perigranular membranes of rat peritoneal mast cells

Beta-adrenergic receptors were characterized by measuring the specific binding of 3H-dihydroalprenolol (DHA) on intact isolated rat peritoneal mast cells (RPMC) and on perigranular membranes derived from purified RPMC granules. The specific binding of 3H-DHA reaches an equilibrium within 30 min at 5 degrees C and is linear with cell number. Scatchard analysis reveals two populations of binding sites on intact cells: with KD = 10.6 +/- 2.6 and 129 +/- 4.7 nM and Bmax of 186 +/- 38 and 1200 +/- 415 fmol/10(6) cells, respectively. Each cell contains 120 X 10(3) high-affinity binding sites and 720 X 10(3) low-affinity binding sites. There appears to be neither alpha-adrenergic nor muscarinic cholinergic receptors on the RPMC. Specific binding of 3H-DHA also occurred to isolated granules with perigranular membranes. The binding was saturable with a single population of binding sites with an affinity (KD) of 7.0 +/- 0.45 nM. Maximum binding (Bmax) was calculated at 56.6 +/- 1.9 fmol/10(9) granules. Subfractionation of granule components demonstrated that the specific binding sites appear to be localized exclusively on the perigranular membrane.

Solubilization and initial biochemical characterization of an IgE-destroying enzyme on rat peritoneal mast cells

Previous studies had demonstrated that incubation of IgE with purified rat mast cells can result in the time and cell concentration-dependent destruction of the ability of the IgE to be bound to specific receptors on rat basophil leukemia cells. The IgE-destroying activity, which has an extremely acid pH optimum, resisted attempts at solubilization using detergents. However, it was solubilized in good yield by use of chaotropic salts and especially KOCN. The soluble activity is stable to freezing and thawing, and to heating to 68 degrees C for 60 min. It is promptly destroyed upon boiling. IgE destruction was linear with time up to 20 min and a series of products, mol. wts 138,000, 92,500, 60,000 and 36,500, are formed during the reaction. No pH optimum for the reaction could be found because, as the pH was lowered below 4.0, the spontaneous destruction of IgE became too great. At pH 4.75 the apparent Km for the reaction was 0.55 microM and Vmax was 0.4 nmoles IgE/10(4) mast cell equivalents/min. IgE-destroying activity could be inhibited by heat-inactivated serum, and by relatively high concentrations of crude alpha 1-antitrypsin, aprotinin, lima bean and soybean trypsin inhibitors and by p-nitroguanidinobenzoate. A large number of other protease inhibitors were inactive.