Richard L. Stevens

Department of Medicine
Harvard Medical School
Brigham and Women's Hospital
Smith Bldg., Rm. 616B
1 Jimmy Fund Way
Boston, MA 02115
Tel: 617-525-1231
Fax: 617-525-1310
email:rstevens@rics.bwh.harvard.edu
5 postdoctoral fellows

My research program is focused on mast cells (MCs) which are tissue-residing immune cells that release a diverse array of biologically active molecules [including cytokines, chemokines, leukotrienes, prostaglandins, amines, proteoglycans, and proteases (1)] when activated through their high-affinity IgE, low-affinity IgG, complement, and protease-activated receptors. Because MCs are present in sea squirts, these cells evolved more than 500 million years ago before adaptive immunity. The fact that they have been conserved for so long documents their importance. No human has been identified that lacks MCs, and studies carried out on MC-deficient mice have revealed that these immune cells are essential for the efficient elimination of bacteria. For example, we have shown that transgenic mice that lack the MC-restricted granule protease mMCP-6 cannot combat Klebsiella pneumonia infections effectively. Despite their beneficial roles in innate and acquired immunity, the presence of increased numbers of activated MCs in the skin of mastocytoma patients, in the bronchial airways of individuals with asthma and chronic allergies, in the skin of patients undergoing extensive fibrosis, in the intestines of helminth-infected individuals, in tumors of cancer patients, and in the joints of patients afflicted with rheumatoid arthritis suggest that these effector cells contribute to the pathology that occurs in numerous clinical disorders. In this regard, my coworkers and I recently showed that exocytosed MC chymase/serglycin proteoglycan complexes cause muscle rhabdomyolysis in a hindlimb ischemia-reperfusion model of hypoxia injury (2).

We have shown that mammalian MCs are a heterogeneous family of hematopoietic cells whose ultimate phenotype is dependent on the tissue microenvironment the mature cell eventually resides. In vitro and molecular biology approaches have been developed to identify the factors and receptors that regulate the differentiation and phenotypic properties of MCs (3). For example, we identified a new cation-dependent, MC-restricted guanine exchange factor/phorbol ester receptor (designated as RasGRP4) that regulates MC development (4). This signaling protein controls what proteoglycans, proteases, and eicosanoids MCs eventually express. By varying the culture conditions, we have been able to induce bone marrow progenitor cells to differentiate and mature into populations of MCs that have varied phenotypes. We have identified a number of novel human and mouse MC-specific genes; we are now investigating why and how these genes and their transcripts are regulated as the MC's microenvironment is altered. Cis-acting elements and trans-acting DNA-binding proteins that regulate the transcription of these genes, and the RNA-binding proteins that regulate the stability of their transcripts are being identified. Transgenic mice have been created that differ substantially in the number of MCs that they have in their tissues. A transgenic/adoptive transfer approach also has been developed in order to address the role of varied MC-derived factors. Recombinant MC-derived proteases have been generated by my group in order to evaluate their physiologic function. Finally, what happens to T cells, epithelial cells, endothelial cells, neurons, fibroblasts, chondrocytes, and smooth muscle cells when they interact with MCs and their granule protease/proteoglycan complexes also are being investigated.

Papers & Publications:

1. Humphries DE, Wong GW, Friend DS, Gurish MF, Qiu W-T, Huang C, Sharpe AH, Stevens RL. Heparin is essential for the storage of specific granule proteases in mast cells. Nature 1999;400:769-772.
2. Abonia JP, Friend DS, Austen WG Jr, Moore FD Jr, Carroll MC, Chan R, Afnan J, Humbles A, Gerard C, Knight P, Kanaoka Y, Yasuda S, Morokawa N, Austen KF, Stevens RL, Gurish MF. Mast cell protease 5 mediates ischemia-reperfusion injury of mouse skeletal muscle. J. Immunol. 2005;174:7285-91.
3. Qi JC, Wang J, Mandadi S, Tanaka K, Roufogalis BD, Madigan MC, Lai K, Yan F, Chong BH, Stevens RL, Krilis SA. Human and mouse mast cells use the tetraspanin CD9 as an alternate interleukin-16 receptor. BLOOD 2006;107:135-142.
4. Yang Y, Li L, Wong GW, Krilis SA, Madhusudhan MS, Sali A, Stevens RL. RasGRP4, a new mast cell-restricted, Ras guanine nucleotide releasing protein with calcium- and diacylglycerol-binding motifs: identification of defective variants of this signaling protein in asthma, mastocytosis, and mast cell leukemia patients; and demonstration of the importance of RasGRP4 in mast cell development and function. J Biol Chem. 2002;277:25756-74.