Browsing by Subject "Id3"

Within the field of immunology, the existence of autoimmune diseases presents a unique set of challenges. The immune system typically protects the host by identifying foreign pathogens and mounting an appropriate response to eliminate them. Great strides have been made in understanding how foreign pathogens are identified and responded to, leading to the development of powerful immunological tools, such as vaccines and a myriad of models used to study infectious diseases and processes. However, it is occasionally possible for host tissues themselves to be inappropriately identified as foreign, prompting an immune response that attempts to eliminate the host tissue. The immune system has processes in place, referred to as selection, designed to prevent the development of cells capable of recognizing the self as foreign. While a great deal of work has been invested in understanding these processes, many concrete answers remain elusive.

Our laboratory, which focuses on understanding the roles of E and Id proteins in lymphocyte development, has established the Id3 knockout mouse as a model of autoimmune disease. Id3 knockout mice develop a disease reminiscent of human Sjӧgren's Syndrome, an autoimmune disease that progressively damages the salivary and lachrymal glands. Continued study of this model has yielded interesting results. These include the identification of CD4+ T cells as initiators of disease as well as the identification of the cytokine Interleukin 13 (IL-13) as a potential causative agent. However, the source of IL-13, its true role as a causative agent of disease, as well as the developmental basis for its elevated expression remained elusive.

To this end, I utilized a reporter gene that enabled me to detect cells producing IL-13 as well as test the effects of IL-13 deletion on disease progression. Using this system, I was able to identify both CD4+ T cells and γδ T cells as major sources of IL-13. I was also able to determine that elimination of IL-13 in Id3 knockout mice was sufficient to block the development of disease symptoms, reinforcing the hypothesis that IL-13 is a causative agent in disease initiation. Finally, I attempted to better characterize the phenotype of cells producing IL-13. These experiments indicated that the T cell receptor (TCR) repertoire of Id3 knockout mice is markedly different than that of wild-type (WT) mice. Furthermore, cells bearing certain TCRs appeared to express IL-13 at dramatically different rates, indicating that certain TCRs may be predisposed to IL-13 particular effector fates.

E and Id proteins are members of the basic helix-loop-helix (bHLH) transcription regulator family. These proteins control a broad range of lymphocyte biology, from the development of multiple lineages to execution of their effector functions. With the development of new experiment models, novel functions of E and Id proteins continued to be discovered. In this thesis, I focused my study on the role of Id2 in gamma delta T cells and CD4+ alpha beta T cells, as well as the role of Id3 in B cells.

Id proteins have been shown to control gamma delta T cell development. Id3 knockout mice demonstrate a dramatic expansion of innate-like Vgamma1.1+ Vdelta6.3+ T cells in the neonatal stage, suggesting that Id3 is an inhibitor of their development. Interestingly, Id3 knockout mice with a B6/129 mix background have much less expansion of the Vgamma1.1+ Vdelta6.3+ T cells compared to mice with pure B6 background. Genetic studies showed that this difference is strongly influences by a chromosome region very close to the Id2 locus. Using the Id2f/f CD4Cre+ mice, I found that Id2 is also an inhibitor of gamma delta T cell development. Deletion of Id2 alone is sufficient to enhance the maturation of these cells in the thymus and induce a moderate expansion of gamma delta T cells in the periphery. This study demonstrated the delicate balance of transcription control in cells of the immune system.

The Id2f/f CD4Cre+ mice also enabled me to study the role of Id2 in peripheral CD4+ alpha beta T cell functions, which was difficult in the past because Id2 knockout mice lack lymph node development. I found that CD4 T cells in these mice have a profound defect in mounting immune responses, demonstrated by a complete resistance to induction of experimental autoimmune encephalomyelitis (EAE). I found that Id2-deficient CD4 T cells fail to infiltrate the central nervous system, and the effector CD4 T cell population is smaller compared to that in control mice. Id2 is important for the survival and proliferation of effector CD4 T cells, and this phenotype was correlated with an increased expression of Bim and SOCS3. This study revealed a novel role of Id2 in the functioning of CD4+ alpha beta T cells.

Switching my focus to B cells, recent next generation sequencing of human Burkitt lymphoma samples revealed that a significant proportion of them have mutations of Id3. This finding suggests that Id3 may be a tumor suppressor gene in the lymphoid system. Utilizing various Id3 knockout and conditional knockout mouse models, I showed that Id3 deficiency can accelerate lymphoid tumor genesis driven by the over-expression of oncogene c-Myc. This work may lead to development of a more realistic mouse model of human Burkitt lymphoma, allowing more mechanistic studies and perhaps preclinical tests of new therapies.