In vitro assays to study role of T cell-derived factors on human B lymphocytes should take into consideration inhibiting effect of large granular lymphocyte subset (CD5 −,CD16 +) that can contaminate B cell preparations

Abstract

In these studies, the inhibitory role of a large granular lymphocyte (LGL) subset (CD5 −,CD16 +) on pokeweed mitogen (PWM)-induced B lymphocyte differentiation was examined. CD5 −,CD16 + LGL cells are the predominant subset of LGL cells and are possibly distinct from other LGL subsets in that they lack B and T cell markers. CD5 −,CD16 + LGL posses abundant FcIgG receptors and previous studies have clearly demonstrated that in the presence of insoluble immune complexes, this LGL subset will inhibit B lymphocyte differentiation in the presence of T cells. In the present studies, we analyzed the inhibiting role of CD5 −,CD16 + LGL cells that had not been activated by immune complexes. B + L preparations obtained by removal of E rosette-forming T cells were further depleted of T lymphocytes by complement-dependent lysis of T cells using a monoclonal antibody reactive to total T cells (Leu-1, CD5 antigen, Becton-Dickinson). B lymphocytes in such B + L preparations failed to differentiate into plasma cells containing intracytoplasmic immunoglobulin (Ig), in the presence of PWM, T cell-derived helper supernatants (THS), and interleukin-2 (IL-2). However, B cells differentiated under these conditions, when B + L preparations were further depleted of CD5 −,CD16 + LGL celld by complement-dependent lysis using a monoclonal antibody (Leu-11) reactive to CD16 antigen of FcIgG receptors present on LGL cells. These studies indicated that CD5 −,CD16 + cells unlike the CD8-positive T suppressor cell, will directly inhibit B lymphocyte differentiation into plasmacytoid cells containing intracytoplasmic Ig when T lymphocytes are not present. However, addition of a few T lymphocytes (< 10%) to purified B + L preparations abrogated the CD5 −,CD16 + LGL cell inhibition of B cell differentiation.