Interaction of Brucella abortus lipopolysaccharide with major histocompatibility complex class II molecules in B lymphocytes

Lipopolysaccharide (LPS), a major amphiphilic molecule located at the outer membrane of gram-negative bacteria, is a potent antigen known to induce sp ecific humoral immune responses in infected mammals. LPS has been described as a polyclonal activator of B lymphocytes, triggering the secretion of an tibodies directed against distinct sugar epitopes of the LPS chain. But, ho w LPS is handled by B cells remains to be fully understood. This task appea rs to be essential for a better knowledge of the anti-LPS humoral immune re sponse. In this study, we examine the internalization of LPS and its intera ction with antigen-presenting major histocompatibility complex (MHC) class II molecules in murine and human B-cell lines. By use of immunofluorescence , we observe that structurally different LPSs from Brucella and Shigella st rains accumulate in an intracellular compartment enriched in MHC class II m olecules. By use of immunoprecipitation, we illustrate that only Brucella a bortus LPS associates with MNC class II molecules in a haplotype-independen t manner. Taken together, these results raise the possibility that B. abort us LPS may play a role in T-cell activation.