Expression of rag2 and V(D)J Recombinase Activity are Reduced in Aged Mice as a Result of Changes in the Bone Marrow Microenvironment: a Dissertation
Date of Completion
Graduate School of Biomedical Sciences, Program in Immunology and Virology
B-Lymphocytes; Bone Marrow Cells; Cell Aging; Gene Rearrangement, B-Lymphocyte; Genes, RAG-1; Mice; VDJ Recombinases; Academic Dissertations
Both humans and mice display an age-related decline in immunity. Reduced generation of mature B cells may be a contributing factor due to reduced entry of mature B cells with novel B cell receptors and specificity for pathogens into the mature B cell pool. In aged mice the numbers of B cell precursors within the bone marrow are diminished; there is a severe reduction in numbers of pre-B cells and an increase in numbers of re-circulated mature B cells. Other defects in developing B cells include reduced expression of rag1 and rag2 when measured in total bone marrow precursor populations. In the pro-B cell stage of development rag expression is essential to the process of V(D)J recombination and the generation of pre-B cells. It was not known prior to this work if rag levels were lower in pro-B cells. In Chapter 2 I show that rag2 expression is reduced in pro-B cells of aged mice. The reduction in rag2 expression is correlated with a loss of V(D)J recombinase activity in pro-B cells and reduced numbers of pre-B cells. This suggests that in aged mice the reduction in rag2 expression is sufficient to result in reduced V(D)J recombinase activity and reduced generation of pre-B cells, thus contributing to fewer pre-B cells in aged mice. Furthermore, I have shown that the loss of rag2 expression and recombinase activity in pro-B cells are the result of age-associated defects in the bone marrow-microenvironment as opposed to cell-intrinsic defects in developing precursors.
In Chapter 3 of this thesis I examine genetic influences on age-related defects in murine B cell development and correlations between bone marrow B cell subsets and peripheral T cell subsets. It was known that longevity and age-related defects in T cell subsets are influenced by genetic differences between strains of inbred mice. The impact of genetic polymorphisms on age-related defects in B cell development had not been previously assessed. Nor was it known if these defects were correlated with age-related changes in peripheral T cell subsets. Here I present evidence that B cell subsets in the bone marrow are influenced by genetic polymorphisms between mice strains. Genetic polymorphisms on Chromosomes 15 and 19 were found to influence the frequency of re-circulated and pre-B cells in the bone marrow of aged mice. Frequencies of bone marrow B cell subsets were compared with peripheral T cell subsets. Interestingly, an association between the frequency of pre-B cells was not observed with either re-circulated B cells in the bone marrow nor peripheral T cell subsets. However the frequency of pre-B cells was inversely correlated with the frequency of B220intIgM+ cells, a subset that was found to correlate with more advanced age-related T cell defects. In addition, frequencies of re-circulated B cells in the bone marrow were found to be associated with less advanced age-related defects in peripheral T cell subsets.
These observations indicate that defects in B cell development, including reduced rag2 expression and V(D)J recombinase activity, are the result of changes in the aged murine bone marrow microenvironment. In addition, a genetic polymorphism located on Chromosome 19 influences the frequency of pre-B cells in aged mice. Furthermore the frequencies of B cell precursors in aged mice are not correlated with peripheral T cell subsets, but are correlated with frequencies of B220intIgM+ cells in the bone marrow. These observations advance our understanding of age-related defects in murine B cell development and may lead to identification of genes that influence B cell development in aged mice and humans as well as to help devise therapeutics aimed at restoring humoral immunity in aged individuals.
Labrie, JE. Expression of rag2 and V(D)J Recombinase Activity are Reduced in Aged Mice as a Result of Changes in the Bone Marrow Microenvironment: a Dissertation. (2004). University of Massachusetts Medical School. GSBS Dissertations and Theses. Paper 236. http://escholarship.umassmed.edu/gsbs_diss/236
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