Graduate School of Biomedical Sciences, Program in Immunology and Virology
Dissertations, UMMS; Proto-Oncogene Proteins c-pim-1; Proto-Oncogene Proteins; Protein-Serine-Threonine Kinases; Immunity, Humoral
Pim (Provirus Integration site for Moloney murine leukemia virus) kinases are a family of three serine/threonine kinases involved in cell cycle, survival and metabolism. These kinases were first identified in malignant cells and are most often associated with their role in cancer. Their role in immunity and lymphocytes is less well known. To date, it has been shown that Pim 1 and/or Pim 2 are important for T lymphocyte survival and activation when the Akt signaling pathway is inhibited by rapamycin. In addition, our laboratory has shown that Pim 2 is critical for BLyS-mediated naive B lymphocyte survival in the presence of rapamycin.
This thesis extends the role(s) for Pim 1 and/or 2 to include functions during B cell activation and the generation of immune responses. We found that during in vitro activation of purified resting splenic B cells from wild type mice with a variety of activators that use multiple signaling pathways, including the BCR, TLR and CD40 receptors, both Pim 1 and 2 kinases were induced by 48 hours post-activation, suggesting that they could play a role in B cell activation and differentiation to antibody secreting or memory B cells. Immunization of Pim 1-/-2-/- knockout mice with T cell dependent antigens showed impairment in antibody and antibody secreting cell generation as well as lack of germinal center formation clearly demonstrating an involvement of Pim 1 and/or 2 in the immune response. FACS examination of B cell populations from naive Pim 1-/-2-/- knockout mice revealed normal levels of splenic marginal zone and follicular B cells and T cells, however, decreased numbers of all peritoneal B cell populations and decreased B cells in Peyer's Patches was seen. An examination of serum antibody found in naive Pim 1-/-2-/- knockout mice showed decreased levels of natural antibody, which is likely due to loss of the peritoneal B1 cells but does not explain the significantly decreased TD immune response. To determine whether the defect was B cell intrinsic or a more complex interaction between B and T cells, we determined whether Pim 1-/-2-/- mice would respond to T cell independent, TI-1 and TI-2, antigens. Antibody production and antibody secreting cell formation were also significantly decreased in these mice supporting our notion of a B cell intrinsic defect. To further examine the B cell response problem, we attempted to establish chimeric mice using either bone marrow derived cells or fetal liver cells from WT or Pim 1-/-2-/- donors so that the B cells were derived from Pim 1-/-2-/- mice and the T cells would be WT. Unfortunately, we were not able to consistently engraft and develop mature Pim 1-/-2-/- B cells, which indicate that there is a stem cell defect in these knockout mice that requires further investigation. Because one of the major failures in activated Pim 1-/-2-/- B cells is the generation of antibody secreting cells, an analysis of the expression of transcription factors IRF-4 and BLIMP-1, known to play a role in this process was carried out. Although IRF-4 induction was not affected by the loss of Pim 1 and 2, the number of cells able to increase BLIMP-1 expression was significantly decreased, revealing a partial block in the generation of ASCs. Taken together the data presented in this thesis reveals a new and critical role for Pim 1 and 2 kinases in the humoral immune response.
Willems, KN. Regulation of Humoral Immunity by Pim Kinases: A Dissertation. (2011). University of Massachusetts Medical School. GSBS Dissertations and Theses. Paper 567. http://escholarship.umassmed.edu/gsbs_diss/567
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