IgE secretion is attenuated by an inhibitor of proteolytic processing of CD23 (Fc epsilonRII).

CD23, the low-affinity IgE receptor, is up-regulated on interleukin (IL)-4-stimulated B cells and monocytes, with a concomitant increase in the release of soluble fragments of CD23 (sCD23) into the medium by proteolytic processing of the surface-bound intact CD23. The effect of inhibition of the processing of CD23 on IgE production in human and mouse cells and in a mouse model in vivo was evaluated. CD23 processing to sCD23 from RPMI 8866 (a human Epstein-Barr virus-transformed B cell line) cell membranes was inhibited by a broad-spectrum matrix-metalloprotease inhibitor, batimastat, with an IC50 of 0.15 microM. Batimastat also inhibited CD23 processing in whole RPMI 8866 cells as well as in IL-4-stimulated purified human monocytes with similar IC50. Batimastat inhibited IgE production from IL-4/anti-CD40-stimulated human tonsil B cells as well as mouse splenic B cells in a manner consistent with inhibition of CD23 processing. Release of soluble fragments of CD23 in the cell supernatants of tonsil B cells was inhibited over the concentration range of 1-10 microM batimastat and intact cell surface CD23 was increased on mouse splenic B cells in the presence of these concentrations of batimastat. IgE production of IL-4-stimulated human peripheral blood mononuclear cells was also blocked by 1-10 microM batimastat, again with comparable inhibition of sCD23 release over the same concentration range. Finally, in a mouse model of IgE production, batimastat inhibited IgE production in response to ovalbumin challenge as determined by serum IgE levels. Taken together, the data support a role of CD23 in IgE production and point to CD23 processing to sCD23 as a therapeutically relevant control point in the regulation of IgE synthesis.

Identification of a soluble, high affinity human interleukin 4 binding protein in normal human urine.

We report the existence of a protein in normal human urine that binds, specifically and with high affinity (Kd approximately 1.9 nM) to human interleukin 4 (IL-4) and thereby prevents the binding of the cytokine to the high affinity receptor. The urinary binding protein has a molecular weight of 40 kD and 23 kD after deglycosylation. The binding protein has been purified by affinity chromatography. It inhibited IL-4-dependent (but not IL-2-dependent) T-cell proliferation. This protein may play a role in vivo in regulating the biological activities of this important immunoregulatory cytokine.

Stimulatory effects of FK156 in a panel of tests designed to detect changes in immune function.

There is a need to evaluate the utility of experimental models in immune function assessment if these are to be accepted in preclinical safety studies. We have evaluated a panel of tests measuring cellularity and functions of the lymphoid system in the Fischer rat in order to determine whether they would detect immunostimulation, rather than suppression. Injection of the peptide immunostimulant FK156 (D-lactyl-L-alanyl-y-D-glutamyl-(L)-meso-diaminopimelyl- (L)-glycine) increased the numbers of macrophages recovered from the peritoneal cavity, and stimulated their activity, as measured by chemiluminescence, adherence, and secretion of interleukin 1. In vitro, T lymphocytes had an increased background incorporation of tritiated thymidine, increased response to sub-optimal concentrations of concanavalin A, and an increase in secretion of interleukin 2 at optimal concentrations of concanavalin A. There was no change in the proliferative responses of B lymphocytes in vitro. Antibody responses to tetanus toxoid in vivo were increased. These changes were not reflected in consistent, statistically significant alterations in the numbers of lymphocytes bearing either lineage markers or the interleukin 2 receptor as a marker of activation.

Immunological studies on paroxetine, a novel anti-depressant drug.

Paroxetine is a novel and selective neuronal 5-hydroxy-tryptamine uptake inhibitor with anti-depressant activity. Paroxetine was examined for its ability to induce adverse immunological reactions, either as a consequence of a specific immune response or by a direct or indirect effect on the immune system. Paroxetine did not react in vitro with protein amino or thiol groups, suggesting that it lacks the capacity to form potentially immunogenic hapten protein conjugates. No anti-paroxetine antibody was detected in plasma or serum samples from patients and rats following oral administration over prolonged periods, or from epicutaneously exposed guinea pigs, or from rabbits given paroxetine in Freund's adjuvant, suggesting that paroxetine does not have the capacity to elicit humoral immune responses. Guinea pigs epicutaneously exposed to paroxetine did not develop contact sensitivity, suggesting that it does not have the capacity to elicit cell-mediated immune responses. These results suggest that paroxetine lacks intrinsic immunogenicity. Anti-SRBC antibody plaque-forming cell responses in mice were unaffected by oral administration of paroxetine, and paroxetine had no significant effect on ex vivo and in vitro murine macrophage phagocytosis of opsonized SRBC or on ex vivo murine splenocyte mitogen responses, suggesting that paroxetine does not exert modulatory effects on the immune system or on macrophage function. These findings, together with the results of pre-clinical safety evaluation studies, suggest that paroxetine is unlikely to have immunotoxic effects.

A simple rapid technique to measure neutrophil or serum bactericidal activity.

A rapid and simple technique to measure both serum and neutrophil bactericidal activity is described. It is based on microtitre equipment and avoids the cumbersome and time consuming serial dilution and plate counting of conventional experiments. A constant concentration of neutrophils and/or serum is incubated with a series of dilutions of bacterial suspensions. Bacterial survival is estimated at various times from their ability to form colonies on agar and the results conveniently expressed as the largest bacterial population that can be eliminated by either neutrophils or serum alone. The technique is as simple and quick as a standard microtitre MBC test commonly used for antibiotics and scoring of the results takes only a few seconds per sample. Data are presented showing the close correlation between results obtained using this technique and those from conventional tests of neutrophil bactericidal activity and phagocytosis-associated chemiluminescence.

Toxicity and immunosuppressive activity of binary combinations of 2'-deoxycoformycin and 2'-deoxyadenosine.

Treatment of mice with 2'-deoxycoformycin (dCf) for 5 days produced inhibition of spleen and lymph node adenosine deaminase (E. C. 3.5.4.4) activity but no hematologic toxicity or weight loss. A 64-fold elevation of erythrocyte dATP was observed. However, if mice were injected with 2'-deoxyadenosine (AdR) in combination with dCf, weight loss, hematologic toxicity, and liver cell necrosis occurred. These mice had a severe blood coagulation defect and a 73-fold elevation of plasma alanine transaminase activity, plasma prealbumin became undetectable, and erythrocyte dATP levels were elevated 1500-fold. Death during treatment appeared to be from acute liver failure since bone marrow toxicity was only detected following termination of treatment. These effects were not seen in mice receiving adenosine in combination with dCf. dCf, either alone or in combination with AdR, inhibited the contact sensitization to oxazalone in mice. The inhibition was associated with signs of systemic toxicity which were more pronounced in the combination-treated groups. If dATP is the toxic metabolic accumulated in the malignant cells of patients treated with dCf, we propose that AdR supplementation of treatment should be considered with extreme caution since severe damage to normal tissues might result.