Date on Master's Thesis/Doctoral Dissertation

8-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Committee Chair

Jala, Venkatakrishna Rao

Author's Keywords

Mast cells; Intestinal cancer; T cells; D6 receptor; Chemokines; Immune surveillance

Subject

Mast cells; Colon (Anatomy)--Cancer; T cells

Abstract

Chronic inflammation promotes a variety of cancers but inflammation also plays an important role in immune surveillance of cancer. Chemokine decoy receptor, D6 scavenges large number of inflammatory chemokines without transducing any signals and thus presumably dampens inflammation. Consistent with this notion, the D6 deficient mice displayed enhanced inflammation in variety of disease models. However, our laboratory observed that absence of D6 caused an unexpected decrease in inflammation and reduced tumor burden in the ApcMin/+ mouse model of intestinal cancer. Intestinal tumors in D6-/-ApcMin/+ mice showed increased mast cell infiltration but their contribution to tumor progression is unknown. Therefore, unravelling the cellular and molecular mechanisms of mast cell mediated regulation of intestinal tumor development is the central theme of this dissertation. Studies described in three specific aims utilize a combination of genetic, molecular and immunologic approaches to establish the importance of mast cells in the D6-/- ApcMin/+ model. Chapter III describes generation and characterization of the mast cell deficient D6-/-SA-/-ApcMin/+ mice. The results showed that the absence of mast cells led to decreased survival of these mice due to rapid progression of the intestinal adenomas. However, mast cells did not have a significant impact on the rate of tumor initiation in this model. In Chapter IV, we established cultures of bone marrow derived mast cells (BMMCs) from WT and D6-/- mice. Analysis of total RNA from these cells by microarrays, real-time PCR showed that chemokine receptors, CCR2 and CCR5 are highly upregulated in D6-/- BMMCs compared to WT cells. The enhanced mRNA expression also correlated well with the enhanced protein and function of CCR2 and CCR5 in D6-/- BMMCs. Further studies will be required to identify the relevance of CCR2 and CCR5 to enhanced mast cell migration into D6-/-ApcMin/+ tumors. In Chapter V, immunofluorescence studies on the extent of mast cell and CD8+ T-cell infiltration into intestinal adenomas of ApcMin/+, D6-/-ApcMin/+ and D6-/- SA-/-ApcMin/+ showed that cytotoxic T-cell infiltration is dependent on mast cell presence in the tumors. In contrast, analysis of D6-/-Rag2-/-ApcMin/+ tumors showed T-cell independent mast cell homing into these tumors. Further studies with cultured mast cells and CD8+ T-cells showed that D6-/- mast cells are capable of efficient antigen presentation to induce proliferation and activation of the cytotoxic potential of T-cells. The data suggests that mast cells act upstream of T-cells in mediating effective immune surveillance of intestinal cancers. These results would have important implications in designing immunotherapeutic approaches involving mast cell mediated anti-tumor immunity.

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