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, proteases, and proteoglycans (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. In support of this conclusion, 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 (2). 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 substantially to the pathology that occurs in numerous clinical disorders. In this regard, we showed that exocytosed MC-restricted protease-heparin complexes cause inflammation and joint destruction in experimental arthritis (3).

We demonstrated 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. For example, we identified a novel cation-dependent, MC-restricted guanine exchange factor/phorbol ester receptor (designated as RasGRP4) that regulates MC development (4,5). 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 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;400:769-72.

2. Thakurdas SM, Melicoff E, Sansores-Garcia L, Moreira DC, Petrova Y, Stevens RL, Adachi R. The mast cell-restricted tryptase mMCP-6 has a critical immunoprotective role in bacteria infections. J Biol Chem. 2007;282:20809-15.

3. McNeil HP, Shin K, Campbell IK, Wicks IP, Adachi R, Lee DM, Stevens RL. The mouse mast cell-restricted tetramer-forming tryptases mMCP-6 and mMCP-7 are critical mediators in inflammatory arthritis. Arthritis Rheum. 2008;58:2338-46.

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.

5. Katsoulotos GP, Qi M, Qi JC, Tanaka K, Hughes WE, Molloy TJ, Adachi R, Stevens RL, Krilis SA. The diacylglycerol dependent translocation of Ras Guanine Nucleotide-Releasing Protein 4 (RasGRP4) inside a human mast cell line results in substantial phenotypic changes including expression of the interleukin 13 receptor IL13Rα2. J Biol Chem. 2008;283:1610-21.