LPS-dependent changes in the expression of 57 kDa and 53 kDa cell membraneproteins without participation of CD14

It is widely presumed that in addition to CD14, other molecules are necessa ry for lipopolysaccharide (LPS)-induced cell activation. In order to shed l ight on some of the biological and biochemical properties of these molecule s, we examined the LPS responsiveness of CD14-negative, ST2 cells. Although ST2 cells do not express CD14 mRNA, they, nonetheless, expressed IL-6 mRNA and synthesized IL-6 protein when incubated with LPS in serum-free medium (i.e. without soluble CD14). Paxlitacel (Taxol(TM)) also induced IL-6 mRNA expression in ST2 cells, while Rhodobacter sphaeroides diphoshoryl lipid A (RsDPLA) inhibited both LPS- and Taxol-induced expression of Br 6 mRNA. Col lectively, these data suggest that LPS, RsDPLA, and Taxol all recognize the same receptor complex on ST2 cells and do not require the participation of CD14. In addition, using antibody raised against the STZ cell membrane fra ction, we detected a set of LPS-specific membrane antigens in murine perito neal macrophages, including two designated p57 (57 kDa) and p53 (53 kDa). T here was no qualitative difference in the expression of p57 and p53 in LPS- responsive, C3H/HeN and LPS-hyporesponsive, C3H/HeJ macrophages. However, a fter stimulating the macrophages with LPS or Taxol, expression of p57 and p 53 was diminished in C3H/HeN macrophages, but not in C3H/HeJ macrophages. P horbol ester (PMA) and A23187 calcium ionophore did not suppress p57 or p53 expression, and the lipid A precursor, PE406, did not bind to either prote in. Thus, p57 and p53 may play important roles in LPS-evoked responses, but they do not appear to serve as LPS receptors.