Relationship between immune system and gram negative bacteria. I. Spontaneous binding of smooth and rough Salmonella to human peripheral blood lymphocytes.

Over the past years many reports have emphasized that either Gram positive or Gram negative bacteria possess the ability to bind spontaneously to human peripheral blood lymphocytes (PBL). Here, bacterial binding to human PBL has been studied by using a smooth (S) Salmonella typhimurium LT-2 and two rough (R) mutants of Salmonella minnesota R 345 (Rb) and R 595 (Re), which possess specific deletions in their lipopolysaccharide (LPS) molecule. Our results provide evidence that all three bacterial strains spontaneously bind to PBL, even though Re and mostly Rb cells display the highest degree of adherence. The three major regions of LPS (O-polysaccharide chain, R core and lipid A) seem to be involved in the binding since adherence is specifically inhibited by pretreating PBL with S- or R-LPS extracted from homologous bacteria. Furthermore, using a panel of monoclonal antibodies to lymphocyte surface antigens, S- and R-Salmonella bacteria bind to T lymphocytes (preferentially T8+ cells), while few B cells are coated by bacteria. Additionally, bacterial binding is significantly reduced by trypsin pretreatment of PBL, this suggesting that proteins (or glycoproteins) of the PBL membrane are involved in the binding.