LIPOPOLYSACCHARIDE MODULATION OF A CD14-LIKE MOLECULE ON PORCINE ALVEOLAR MACROPHAGES

Cluster of differentiation antigen 14 (CD14) functions as a receptor f or lipopolysaccharide (LPS) LPS-binding protein (LBP) complexes. Becau se LPS has varying effects on CD14 expression in vitro, we evaluated C D14 expression in response to LPS with a fully differentiated macropha ge phenotype, the alveolar macrophage. By using flow microfluorometric analysis and a radioimmunoassay with an anti-human CD14 monoclonal an tibody (My4) that cross-reacts with porcine CD14, we found that macrop hages stimulated with LPS for 24 h exhibited a two- to fivefold increa se in CD14-like antigen compared with unstimulated cells, At low conce ntrations of LPS, up-regulation of the CD14-like antigen was dependent on serum; at higher concentrations of LPS, serum was not required, In the absence of serum a 10-fold higher dose of LPS (10 ng/ml) was requ ired to increase CD14-like expression. In addition, LPS-induced CD14-l ike up-regulation correlated with secretion of tumor necrosis factor-a lpha, regardless of serum concentration, Blockade with My4 antibody si gnificantly inhibited LPS-induced tumor necrosis factor-alpha secretio n at 1 ng/ml of LPS, However, inhibition decreased as we increased the LPS concentration, suggesting the existence of CD14-independent pathw ays of macrophage activation in response to LPS. Alternatively, My4 ma y have a lower affinity for the porcine CD14 antigen than LPS, which m ay have only partially blocked the LPS-LBP binding site at high concen trations of LPS, Therefore, these data suggest that LPS activation of porcine alveolar macrophages for 24 h increased CD14-like receptor exp ression. The degree of CD14-like up-regulation was related to LPS conc entration, however, activation did not require the presence of serum a t high concentrations of LPS.