1. an immunologically important lymphocyte that is not thymus dependent, is short-lived, and resembles the bursa-derived lymphocyte of birds in that it is responsible for the production of immunoglobulins; it is the precursor of the plasma cell and expresses surface immunoglobulins (SIGS) but does not release them. It does not play a direct role in cell-mediated immunity. B lymphocyte can be characterized immunophenotypically by CD19 surface markers.
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