Bovine B cells : B lymphopoiesis and the Generation of Primary Immunoglobulin Repertoire in Fetal Cattle
Year: 2012
Type: dissertation
Abstract: Immunological research is dominated by studies on man and mouse, however, only some aspects of this field are universal among vertebrates. Whilst the production of T cells is universal, B cell production cannot be extrapolated from one species to another. As such, ruminant B cell biology has distinctive features not similar to the conventional man or mouse based models. Cattle are large long-lived ruminants, of major significance globally. The bovine ileal Peyer s patch, an organ of B cell follicles along the gut, is where V(D)J immunoglobulin gene rearranged B cells proliferate, however it is not known where and how the DNA rearrangements take place before the B cells enter these follicles. Furthermore, it is unclear whether post-recombinatorial modifications, such as somatic hypermutation or gene conversion, facilitate the generation of more antibody specificities of the immunoglobulin genes in these follicles. Herein, the bovine immunoglobulin light chain genomic locus was characterized and only a moderate number of functional gene segments that cause low combinatorial antibody diversity were found. The lambda locus is the larger of the two light chain loci, containing 25 functional variable gene segments, compared to the kappa locus, which contains only eight. Functional genes comprise less than half of all the variable genes in both loci, the remainder representing unfunctional pseudogenes. The immunoglobulin genes of the fetal ruminant ileal Peyer s patch can possibly be further modified. Accordingly, the expression of activation-induced cytidine deaminase (AID), a mutator protein, was demonstrated here in fetal cattle ileal Peyer s patch. Sequencing of expressed heavy chain variable genes in these follicles showed ongoing hypermutation. The mutations were concentrated on the complementarity determining regions (CDR) of the variable genes, and on the hotspot target sequences of AID. AID-dependent mutations have usually been ascribed to antigen dependent affinity maturation, but this work demonstrates mutations in fetal immunoglobulin genes before exposure to external antigen. Bovine B lymphopoiesis is studied here, its localization in the fetal cattle in particular. By analyzing the expression of RAG1 and RAG2, which take part in the rearrangement of immunoglobulin genes, active B lymphopoiesis was demonstrated in fetal bone marrow and lymph node. The expression of surrogate light chain genes VPREB1 and IGLL1 was also shown in these same tissues. The expression of these genes implicated that a pre-B cell stage exists in cattle. This was further confirmed by the presence of a phenotypic pre-B cell population in fetal bone marrow and lymph node. VPREB2 and VPREB3 were expressed differently from the other surrogate light chain genes, which indicate that their function in cattle might not be related to pre-B cells. Overall, B lymphopoiesis was shown to take place in fetal, but not in adult, bovine tissues. Pre-B cell related genes RAGs, VPREB1 and IGLL1 were not expressed in adult tissues. Further, adult bone marrow cells were not able to differentiate into B lineage cells in cell culture. These results suggest that no new immunoglobulin rearrangements are generated during bovine adult life. Thus it is likely that the animal manages its whole life with the peripheral B cell pool produced during the fetal and neonatal period.
Source: Työväentutkimus Vuosikirja
Author: Anna Ekman
Language: English
Topic: T-cell and B-cell Immunology
Subfield: Immunology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1557933515