The research in my laboratory is primarily directed toward understanding the molecular mechanisms involved in the recruitment of pro-inflammatory cells to sites of chronic inflammation. We have focused our attempts to understand the role of eosinophil effector function by creating transgenic mouse models altering the level and location of cytokine production through the use of different enhancer and promoter constructs. My laboratory collaborates extensively with Dr. Jamie Lee (Mayo Clinic Scottsdale) in these studies of eosinophils and their associated effector functions. A critical part of this research has been the generation and establishment of mouse models of human diseases such as asthma, allergic inflammation and hypereosinophilic syndromes. Our studies on the ectopic expression of IL-5 have shown that this cytokine uniquely augments eosinophil numbers and leads to the establishment of pathologies associated with chronic inflammation. Some of these mouse models are described below.

Characterization of Pathologies in Transgenic Mice Expressing IL-5

Eosinophils are bone-marrow derived polymorphonuclear granulocytes, and are predominately tissue-dwelling cells. The peripheral blood of healthy individuals contains only approximately 2% eosinophils in the total white blood cell population. Cytokines and chemokines are critically important both in regulating eosinophil maturation and activation and in recruiting eosinophils to remote sites of injury and/or inflammation. Interleukin-3 (IL-3), interleukin-5 (IL-5) and granulocyte/macrophage-colony stimulating factor (GM-CSF) promote the formation of eosinophils within the marrow as well as augment the effector activities of the mature eosinophil. The components released from the specific granules of eosinophils during degranulation have been implicated in tissue damage associated with eosinophil infiltrates in humans and primates.

We have generated transgenic mice designed to express murine IL-5 constitutively from a cDNA:genomic fusion construct (i.e., no endogenous IL-5 regulatory sequences) using different enhancer/promoter sequences to achieve tissue-specific expression. In each case, the tissue/cell type was chosen based on clinical observations of gene expression and include:

1. Hypereosinophilic syndromes - T cell specific expression using regulatory elements from the murine CD3d gene.
2. Atopic dermatitis and allergic skin diseases - Basal keratinocyte specific expression using the promoter from the human keratin-14 gene.
3. Asthma and allergic respiratory diseases - Lung epithelial expression in the airways and alveolar spaces using the regulatory elements from the rat Clara cell secretory 10 kD protein gene (CC10).

The transgenic lines derived from each set of regulatory elements all exhibit high (and comparable) levels of serum IL-5. However, in each case localized expression of IL-5 resulted in unique changes in the leukocytes recruited to a given tissue or organ and resulted in inflammatory pathologies specific to the site of expression. For example, line NJ.1638 shows dramatic increases in total WBC counts and exhibit a profound hypereosinophilic disease. Line NJ.692 exhibits alopecia and skin lesions, and line NJ.1726, discussed in more detail below, shows characteristics common to human asthma patients. We are continuing our study of these animals and of the role of eosinophils in disease using these animals as model systems.

Several studies indicate that eosinophils may participate in host responses to certain types of cancer. Specifically, eosinophils are often found to infiltrate cancerous solid tumors of the lung, colon, pancreas, mammary tissue, cervix, bladder, and skin. Data from some of these studies further suggest that eosinophil infiltration may lead to tumor regression and can be a prognostic indicator of tumor cell growth (Tepper et al. (1992)). Tumor cell lines secreting mIL-4 elicit a host immune response resulting in eosinophil tumor infiltration and a significant decrease in tumor mass. The regression of the tumors is characterized by an early and prominent influx of eosinophils, leading to a subsequent recruitment of other proinflammatory cells and tumor cell destruction. Depletion of granulocytes (eosinophils and neutrophils) by passive immunization prevent tumor necrosis, showing the requirement of these cells in tumor killing. Because IL-4 has many other effects on the host immune system (and other host cell functions), other mechanisms cannot be excluded; however, the recruitment and activation of eosinophils appear to be an important component of tumor regression. We are extending these studies to further define the role of eosinophils, neutrophils and specific eosinophil granule proteins in tumor regression in mouse models.