Leukocyte recruitment into human skin transplanted onto severe combined immunodeficient mice induced by TNF-alpha is dependent on E-selectin.

In order to study the in vivo role of E-selectin in human inflammation, we have developed a model in which human skin is transplanted onto severe combined immunodeficient (SCID) mice. The grafted skin closely resembles normal skin and retains its human vasculature. After intradermal injection of rTNF-alpha, human E-selectin was rapidly up-regulated on dermal microvessels, with significant expression (determined immunohistochemically) at 1 h postinjection and maximum expression at 2 h postinjection. To study the functional role of E-selectin, a murine Ab against human E-selectin (mAb HEL 3/2) was developed that inhibited the in vitro adhesion of both human U937 cells and murine 32D cells to TNF-alpha-stimulated human endothelial cells. After intradermal injection of TNF-alpha, large numbers of murine leukocytes migrated into the grafts within 2 h. Intravenous injection of the antihuman E-selectin mAb 3/2 completely inhibited murine white blood cell (WBC) transmigration into the skin grafts, but an isotype-matched control Ab that also bound to human endothelium had no effect. Antihuman E-selectin mAb 3/2 was also able to inhibit the migration of i.v. 51Cr-labeled human neutrophils. These findings demonstrate that E-selectin is important in early white blood cell adhesion events and is required for TNF-alpha-induced white blood cell transmigration in the human/SCID mouse chimeric model.

Structure-function relationships of interleukin-3. An analysis based on the function and binding characteristics of a series of interspecies chimera of gibbon and murine interleukin-3.

IL-3 is a glycoprotein cytokine involved in the hematopoietic response to infectious, immunologic, and inflammatory stimuli. In addition, clinical administration of recombinant IL-3 augments recovery in states of natural and treatment-related marrow failure. IL-3 acts by binding to high affinity cell surface receptors present on hematopoietic cells. To determine the site(s) at which IL-3 binds to it receptor, we analyzed a series of interspecies chimera of the growth factor for species-specific receptor binding and biological activity. The results suggest that IL-3 binds to its receptor and triggers a proliferative stimulus through two noncontiguous helical domains located near the amino terminus and the carboxy terminus of the molecule. To corroborate these findings, we have also mapped the binding epitopes of 10 mAb of human or murine IL-3, and have defined four distinct epitopes. Two of these epitopes comprise the amino-terminal receptor binding domain. A third epitope corresponds to the carboxy-terminal receptor interactive domain, and the fourth epitope, apparently not involved in the interaction of IL-3 and its receptor, lies between these sites. And on the basis of sandwich immunoassays using pairs of these mAbs, the two receptor interactive regions appear to reside in close juxtaposition in the tertiary structure of the molecule. These results provide a correlation of the structure-function relationships of IL-3 that should prove useful in evaluating the details of IL-3-IL-3 receptor interaction and in the rational design of clinically useful derivatives of this growth factor.

Molecular cloning and expression of the cDNA for a novel alpha 1-adrenergic receptor subtype.

A novel alpha 1-adrenergic receptor subtype has been cloned from a bovine brain cDNA library. The deduced amino acid sequence is that of a 466-residue polypeptide. The structure is similar to that of the other adrenergic receptors as well as the larger family of G protein-coupled receptors that have a presumed seven-membrane-spanning domain topography. The greatest sequence identity of this receptor protein is with the previously cloned hamster alpha 1B-adrenergic receptor being approximately 72% within the presumed membrane-spanning domains. Localization on different human chromosomes provides evidence that the bovine cDNA is distinct from the hamster alpha 1B-adrenergic receptor. The bovine cDNA clone expressed in COS7 cells revealed 10-fold higher affinity for the alpha 1-adrenergic antagonists WB4101 and phentolamine and the agonist oxymetazoline as compared with the alpha 1B receptor, results similar to pharmacologic binding properties described for the alpha 1A receptor. Despite these similarities in pharmacological profiles, the bovine alpha 1-adrenergic receptor is sensitive to inhibition by the alkylating agent chloroethylclonidine unlike the alpha 1A-adrenergic receptor subtype. In addition, a lack of expression in tissues where the alpha 1A subtype exists suggests that this receptor may actually represent a novel alpha 1-adrenergic receptor subtype not previously appreciated by pharmacological criteria.

Inhibition of receptor binding and neutralization of bioactivity by anti-erythropoietin monoclonal antibodies.

We have generated four high affinity monoclonal antibodies (MoAbs) to recombinant human erythropoietin (EPO). All four MoAbs immunoprecipitate radioiodinated native EPO, and the concentrations of MoAbs required for maximum binding range from 10 nmol/L to 100 nmol/L. Two MoAbs, designated Group I MoAbs, bind to an epitope within the N-terminal 20 amino acids of EPO and also immunoprecipitate sodium dodecyl sulfate (SDS)-denatured EPO. Two other MoAbs (Group II MoAbs) do not immunoprecipitate SDS-denatured EPO and do not bind to any of the eight endo C fragments of EPO. We first used murine erythroleukemia (MEL) cells to test the MoAbs for inhibition of EPO-receptor binding. MEL cells, although unresponsive to EPO, express 760 high affinity receptors for EPO per cell (Kd = 0.24 nmol/L). To assay our MoAbs, MEL cells were grown as monolayers on fibronectin-coated Petri dishes and incubated at 4 degrees C with radioiodinated EPO. Group I MoAbs do not inhibit binding of radioiodinated EPO to the MEL EPO-receptor, but Group II MoAbs do inhibit binding in a dose-dependent manner. We next examined the neutralization of EPO bioactivity by our MoAbs, using EPO-dependent cell line. Only Group II MoAbs inhibit a newly developed EPO-dependent cell growth, demonstrating that inhibition of EPO-receptor binding correlates with neutralization of EPO bioactivity.