Receptor interactions on the membrane of resting and activated B cells

Abstract

LIPOPOLYSACCHARIDE (LPS) activates one-third of the B cells in mouse spleen, inducing proliferation and maturation to immunoglobulin secretion¹. The surface structure functioning as receptor in the triggering process is specific for the lipid A moiety of LPS², and is encoded by a gene mapped on chromosome 4 (ref. 3), for which two nonfunctional alleles are known (refs 4, 5 and A. C. and T. Meo, in preparation). We have recently described an antiserum which seemed specific for that LPS receptor (LPSR) on the basis of morphological, functional and genetic evidence^6,7. The polyclonality of B cell responses to LPS⁸ has excluded the participation of immunoglobulin combining sites in the process of triggering. The existence of two LPS nonresponder mutants, which display normal triggering behaviour with other reagents and a normal complement of immunoglobulin positive cells^5,9, also suggested that LPS activation proceeds independently of surface immunoglobulin receptors. The finding of the inhibition of LPS activation by anti-immunoglobulin antibodies, however, suggested that mitogen receptors and surface immunoglobulins could be interacting on the B-cell membrane¹⁰. We report here direct morphological evidence that supports the existence of such interactions.