Binding of bacterial lipopolysaccharide to murine lymphocytes

Does LPS activate lymphocytes by binding to a specific cell-surface receptor or by nonspecific hydrophobic interaction with the plasma membrane? We examined this question by detecting cell-bound LPS using immunofluorescence microscopy and radiobinding techniques. LPS binding to splenic lymphocytes from C3H/St mice has characteristics of specific binding: saturability with respect to dose and time, selectivity for a subclass of B-cells, and a correlation between binding and mitogenesis. 125I-labeled LPS bound to cells and analyzed quantitatively by SDS-PAGE separated into 3 major components: peaks 1, 2, and 3 (1 equals the fastest moving). Lymphocytes preferentially bound peak 1, murine RBC peaks 1 and 2, and macrophages peak 2. In contrast, specific antibody preferred peaks 2 and 3. Differential staining of gels suggested that peak 3 is carbohydrate-rich and peak 1 is lipid-rich. LPS was released from these cells at different rates. We conclude that selectivity of LPS binding may be reflected in preferential binding of LPS subunits of different size and/or composition, as well as differential retention of bound LPS.