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Studies of bovine B cell development
This dissertation was to study the sites of B cell development, the mechanisms of Ig diversification, the time when diversification occurs, the B cell repertoire during development and usage of Ig light chains in cattle.^ The expression of TdT, RAG-1 and RAG-2 was detected in spleen in young animals but not in old animals indicating that gene rearrangement of B cells takes place in spleen and is restricted to a short period of time during early development in cattle.^ To determine the mechanisms by which cattle create a diverse Ig repertoire, genomic rearrangement patterns and V$\lambda$ sequences of cDNA and germline genes were examined. Few rearrangements, potential donor sequences in germline pseudogenes and point mutations in the cDNAs were found. These data suggest that cattle primarily use gene conversion to create a diverse Ig repertoire and somatic hypermutation may be used to refine the Ig repertoire upon antigen challenge.^ To investigate when diversification occurs, V$\lambda$ IPP cDNA were compared between young and old animals. Many diverse nucleotides were found in young animals as that in old animals indicating that the diversification takes place in the very early stage of development.^ To determine the peripheral Ig repertoire during development, expression of peripheral light chains of an animal at different ages was examined. Diversity clustered in the CDRs was increased and different clones which were present in the periphery at a low level in neonatal animals were found to be expanded in older animals. These data indicate that the peripheral Ig repertoire is ligand-selected and clonally expanded by positive selection.^ To investigate the control of $\kappa$/$\lambda$ usage, expression and germline $\kappa$/$\lambda$, V$\kappa$ and C$\kappa$ repertoire were examined. The ratio of expressed $\kappa$/$\lambda$ was high in IPP and spleen, but it was low in the periphery. Additionally, similar numbers of $\kappa$/$\lambda$ genes were found in the germline and V$\lambda$ cDNA sequences were found to be as diverse as that of V$\lambda$. In contrast, C$\kappa$ possesses a low homology to other primarily $\kappa$ expressing mammals. These data suggest that a post-transcriptional control may govern the usage of $\kappa$/$\lambda$ in cattle. ^
Biology, Molecular|Health Sciences, Immunology
"Studies of bovine B cell development"
(January 1, 1995).
Doctoral Dissertations Available from Proquest.