Surface Phenotype of LPS-Binding Murine Lymphocytes

Abstract

LPS+ murine lymphocytes were characterized by determining their surface phenotype using double-labeling immunofluorescence. In the spleen, 40% of cells were LPS+.mu.+ (B cells), 5% were LPS+Thy1.2+ (T cells) and 5% were LPS+ cells bearing neither .mu. nor Thy1.2 (null cells). Peripheral lymph nodes contained 11% LPS+ B cells and 2% LPS+ T cells, and mesenteric lymph nodes contained 15% LPS+ B cells and 3% LPS+ T cells. The 4% LPS+ cells in Peyer''s patches were all B cells, and the thymus contained 4% LPS+ T cells. Only the spleen contained LPS+ null cells. Within each lymphoid organ examined, the fraction of total lymphocytes identified as LPS+.mu.+, LPS+Ia+ or LPS+.delta.+ was similar, indicating that LPS+ B cells possessed the surface phenotype .mu.+Ia+.delta.+, characteristic of a mature B cell. This conclusion was supported by the absence of LPS+.mu.+Ia+.delta.+ cells in newborn spleens. The fraction of .mu.+Ia+.delta.+ cells which also binds LPS was highest in spleen and lowest in Peyer''s patches. Assuming that cells are, on the average, more mature in the progression from spleen to lymph nodes to Peyer''s patches, it would appear that LPS+ cells are a less mature fraction of the .mu.+Ia+.delta.+ pool, distinguished by the presence of an LPS binding site or receptor. These data illustrate selective binding of LPS predominantly to mature B cells, but also to small numbers of null cells and T cells. The relationship of this binding to cell activation is discussed by considering the characteristics of cells which can be activated by LPS to clonal growth or differentiation under appropriate conditions.