The Naïve B Cells are the Lymphocytes with the Highest Anionic Phospholipid Binding Ratios

Abstract

Phospholipids (PLs) are the target for the clearance of apoptotic cells, and for the innate defense against malignant cancers or microbial infections. Several types of receptors for PLs were described on T lymphocytes, but not yet on B lymphocytes. To detect PLs binding lymphocytes two assays were used: a-FITC labelled liposomes, b-Petri dish coated with different PLs. The phenotype of lymphocytes was determined by FACS, using anti-CD mAb and anti-Ig polyclonal antibodies. Human lymphocytes bind PLs, the binding ratio decreases in the order phosphatidylserine (PS), cardiolipin (CL), phosphatidylethanolamine, and phosphatidylcholine. In healthy blood donors (n=17), 29% of B lymphocytes, 17% of NK cells, 9% of TCD4 + , and 4% of TCD8 + bind PS. Among B cells, the binding ratio varies with the subset, 49% for naïve cells (sIgM + sIgD + ), 42% for sIgA + , and 15% for sIgG + B cells. PL binding was not affected by the CD5 phenotype of B lymphocytes, nor by the HIV status of the donors (n=16) or the presence in the sera of IgG anti-CL antibodies. Pretreatment of lymphocytes with proteases inhibited the binding of PL, suggesting that binding is due to surface proteins. For each type of lymphocytes the various kinds of surface proteins which bind lipids, pattern recognition receptors, surface immunoglobulins, the lipid antigen presenting molecules CD1, and the CD1-restricted lipid antigen reactive TCR of NKT cells, are discussed.