Analysis of three human interleukin 5 structures suggests a possible receptor binding mechanism

Neutralizing monoclonal antibodies can potentiate IL-5 signaling

IL-5 is a major determinant in the survival, differentiation and effector-functions of eosinophils. It mediates its effect upon binding and activation of a membrane bound receptor (R), composed of a ligand-specific alpha-chain and a beta-chain, shared with the receptors for IL-3 and granulocyte-macrophage colony-stimulating factor. We have generated and mapped the epitopes of three monoclonal antibodies (mAb) directed against this cytokine: the strong neutralizing mAb 5A5 and 1E1, and the very weak neutralizing mAb H30. We found that H30 as well as 5A5 can increase proliferation above the level induced by human (h)IL-5 alone, in a JAK-2-dependent manner, and at every sub-optimal hIL-5 concentration analyzed. This effect is dependent on mAb-mediated cross-linking of IL-5R complexes, and is only observed on cell lines expressing a hybrid human/mouse IL-5Ralpha-chain. We discuss these findings in view of the stoichiometric and topological requirements for an activated IL-5R. Since humanized anti-IL-5 mAb are currently in clinical testing, our findings imply that such mAb should be carefully evaluated for their potentiating effects.

Structure of the complete extracellular domain of the common beta subunit of the human GM-CSF, IL-3, and IL-5 receptors reveals a novel dimer configuration

The receptor systems for the hemopoietic cytokines GM-CSF, IL-3, and IL-5 consist of ligand-specific alpha receptor subunits that play an essential role in the activation of the shared betac subunit, the major signaling entity. Here, we report the structure of the complete betac extracellular domain. It has a structure unlike any class I cytokine receptor described thus far, forming a stable interlocking dimer in the absence of ligand in which the G strand of domain 1 hydrogen bonds into the corresponding beta sheet of domain 3 of the dimer-related molecule. The G strand of domain 3 similarly partners with the dimer-related domain 1. The structure provides new insights into receptor activation by the respective alpha receptor:ligand complexes.

The morph server: a standardized system for analyzing and visualizing macromolecular motions in a database framework

The number of solved structures of macromolecules that have the same fold and thus exhibit some degree of conformational variability is rapidly increasing. It is consequently advantageous to develop a standardized terminology for describing this variability and automated systems for processing protein structures in different conformations. We have developed such a system as a 'front-end' server to our database of macromolecular motions. Our system attempts to describe a protein motion as a rigid-body rotation of a small 'core' relative to a larger one, using a set of hinges. The motion is placed in a standardized coordinate system so that all statistics between any two motions are directly comparable. We find that while this model can accommodate most protein motions, it cannot accommodate all; the degree to which a motion can be accommodated provides an aid in classifying it. Furthermore, we perform an adiabatic mapping (a restrained interpolation) between every two conformations. This gives some indication of the extent of the energetic barriers that need to be surmounted in the motion, and as a by-product results in a 'morph movie'. We make these movies available over the Web to aid in visualization. Many instances of conformational variability occur between proteins with somewhat different sequences. We can accommodate these differences in a rough fashion, generating an 'evolutionary morph'. Users have already submitted hundreds of examples of protein motions to our server, producing a comprehensive set of statistics. So far the statistics show that the median submitted motion has a rotation of approximately 10 degrees and a maximum Calpha displacement of 17 A. Almost all involve at least one large torsion angle change of >140 degrees. The server is accessible at http://bioinfo.mbb.yale. edu/MolMovDB

Biology of IL-5 in health and disease

LEARNING OBJECTIVES

Reading this article will increase the readers' knowledge of the biology of interleukin-5 (IL-5), an important cytokine. The immune and inflammatory responses of any organism are the basis of the defense mechanism ensuring its survival. The role of IL-5 in these processes, as well as in the pathogenesis of various diseases has been discussed along with the effects of various pharmacologic agents on the production and function of IL-5.

DATA SOURCES

A detailed literature search was performed. Studies considered relevant and important, in all languages, which involved humans and animals were used.

STUDY SELECTION

Information was obtained only from peer reviewed journals.

RESULTS

Interleukin-5 is normally produced by T-cells, mast cells, and eosinophils while Reed Sternberg and Epstein Barr virus (EBV) transformed cells also produce IL-5. Monoclonal antibodies (mAb) to IL-5 are potent inhibitors of IL-5 mediated tissue damage, secondary to eosinophil infiltration. The majority of the studies on IL-5 are preliminary, often the information is obtained from animal studies or in vitro systems and occasionally from pathologic tissue analysis. This along with the absence of confirmatory studies is a limiting factor. Nonetheless, the role of IL-5 in allergic and immunologic disease and asthma may be central to their pathogenesis.

CONCLUSIONS

Interleukin-5 is an important molecule that is participant to many processes that maintain health and are involved directly or indirectly in the pathogenesis of disease. Some pharmacologic agents can modify IL-5 production in vivo. Development of selective inhibitors of IL-5 may have a potential use for specific therapy of certain autoimmune, inflammatory, and neoplastic diseases.