IN-VITRO EFFECT OF BACTERIAL LIPOPOLYSACCHARIDE ON THE CYTOTOXICITY OF HUMAN NATURAL-KILLER-CELLS

Preincubation with a number of mediators of infection, such as Gram ne gative bacteria (S. typhi), bacterial lipopolysaccharide (LPS), tumor necrotic factor-alpha (TNF-alpha), and interleukin-2 (1L-2), significa ntly increases natural killer (NK) cell activity in samples of human p eripheral blood mononuclear cells (PBMC), without changing the levels of either the phenotypic CD16/56 or stimulatory CD25 marker. We now re port similar results after preincubation of highly purified NK cell pr eparations (CD16+56 > 95%; the rest corresponding to CD3(+) T-cells) w ith either S. typhi, TNF-alpha or IL-2. However, in similar experiment s, LPS inhibits, in a dose-dependent manner (final cone. 2.5, 5.0 or 1 0.0 mu g/mL), NK.cell cytotoxicity against K-562 tumor cells. Preincub ation of purified NK cells with LPS (25 mu g/mL; 10 and 30 min) produc ed significant alterations in the tyrosine phosphorylation/dephosphory lation pattern of several intracellular proteins, including a signific ant increase (10 min) in the phosphorylation of the 120; 100; 72 and 5 9 kDa proteins, followed (30 min) by the essentially complete desphosp horylation of the p59 protein. Qualitatively similar results were obta ined at lower LPS concentrations e.g., range 2.5 to 20 mu g/mL. The ab sence of phosphoproteins in the 40-44 kDa range, known to be present a fter incubation of monocytes with LPS, raises the possibility that the se ''class'' of proteins may be critical in explaining the LPS inhibit ory effect on NK lytic function. Our finding may contribute to a bette r understanding of the mechanisms involved in the complex in vivo inte raction between LPS, monocytes and NK cells.