Caractérisation phénotypique et fonctionnelle des lymphocytes B dans la lymphocytose polyclonale chronique B

Authors: Massinga Loembé, Marguerite
Advisor: Darveau, AndréDelage, Robert
Abstract: Persistent polyclonal B cell lymphocytosis (PPBL) is an unusual haematological disorder, mainly detected in adult female smokers, that shares features of both benignity (polyclonal expansion, polyconal IgM secretion, lack of clinical symptoms, stable and mostly uneventful course); and features of malignancy (atypical binucleated cells, multiple bcl-2/Ig translocations, chromosome 3 anomalies, bone marrow involvement). Still, these morphological and clonal genetic anomalies have not been restricted to a distinctive B cell subset, and the apparent heterogeneity of the involved cellular population has long impeded further characterization of the syndrome. The aim of our research was to formally identify the population involved in the lymphocytosis, to gain some insight into the mechanisms at play in its development and to evaluate the risk for subsequent transformation in patients. Over the recent years, technical inputs from the molecular field have largely contributed to a better discrimination of the various B cells subsets and, by extension, of B cell lymphoid disorders. Thus, detailed immunophenotypic studies conducted in numerous PPBL patients allowed us to definitely circumscribe the disorder to IgD+IgM+CD27+ B lymphocytes, whereas exhaustive molecular analysis of immunoglobulin genes’ variable regions has corroborated the memory status of these cells. Yet, molecular signature of the antigenic selection process, the characteristic of a T-dependent immune response, was not detected. Sequencing of the CD40 and AID genes, key regulators in the diversification and affinity maturation of the immunoglobulin receptor, was additionally carried out and expression of both molecules was assessed. No anomaly was evidenced for either gene. In light of those observations, we conclude that a differentiation block in PPBL B lymphocytes is unlikely. Rather, we propose that defects in the affinity maturation process, namely impairment of the antigenic selection mechanism, allows the survival of low affinity IgD+IgM+CD27+ memory B lymphocytes in PPBL patients. Conversely, these cells could be related to the as yet scantily characterized IgD+IgM+CD27+ memory B cell subset from the splenic MZ, also found in the blood, and presumably derived from a germinal centre independent diversification pathway. Altogether, our results contributed to the elaboration of an accurate clinical definition for PPBL, and delineated avenues for future investigations regarding both the pathological aspects of the disorder and its purely fundamental biologic ramifications.
Document Type: Thèse de doctorat
Issue Date: 2004
Open Access Date: 11 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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