Lack of CD40-dependent B-cell proliferation in B lymphocytes isolated frompatients with persistent polyclonal B-cell lymphocytosis

Persistent B-cell lymphocytosis (PPBL) is a haematological disorder diagnos ed primarily in adult female smokers that is characterized by a polyclonal increase in peripheral blood B lymphocytes and a moderate elevation of seru m IgM. B lymphocyte-associated cellular abnormalities, such as the occurren ce of multi-lobed nuclei, increased bcl2/ Ig gene rearrangements and the id entification of an extra long-arm chromosome (i3)(q10) in the B-cell popula tion, indicate that PPBL, could be part of a multi-step process leading to the emergence of a malignant B Lymphoproliferation. However, the resulting impact on cellular functional properties remains to be elucidated. Our goal was to address that aspect via the study of B-cell activity following stim ulation through CD40, a key molecule of the tumour necrosis factor receptor superfamily involved in B lymphocyte development, In contrast to normal B cells, PPBL B lymphocytes were unable to respond to the proliferative signa l delivered in vitro by CD40, indicating a defect in the CD40 activation pa thway. Polymerase chain reaction amplification and sequencing of the recept or as well as FACScan analysis of patient B lymphocytes dismissed the possi bility of a defect in either CD40 structure or expression. Moreover, Wester n blot analysis of tyrosine phosphorylation. an early event in the CD40-sig nalling cascade, was similar in patients and controls, leading to the concl usion that the defect affecting B lymphocytes in PPBL, patients is probably located downstream of that signalling cascade.