HEPARIN-BINDING PROTEIN (CAP37) IS INTERNALIZED IN MONOCYTES AND INCREASES LPS-INDUCED MONOCYTE ACTIVATION

Previous studies have shown that the neutrophil-derived heparin-bindin g protein (MBP), also known as CAP37 or azurocidin, potentiates the LP S-induced release of proinflammatory cytokines (TNF-alpha, IL-I, and P L-g) from isolated human monocytes, To date, the mechanisms by which H BP enhances LPS-induced monocyte activation have not been elucidated, and it is not known whether HBP also increases the LPS-induced product ion of other bioactive substances, We studied human monocytes activate d by recombinant human HBP and LPS and their interaction with the LPS receptor CD14. We hypothesized that the stimulatory effect of HBP on t he LPS-induced release of proinflammatory mediators from monocytes was mediated by specific binding of HBP to monocytes, which resulted in a n up-regulation of CD14. Our results demonstrated that HBP alone (10 m u g/ml) stimulated the production of TNF-alpha from isolated monocytes , In addition, HBP had an additive effect on LPS-induced production of TNF-alpha and PGE(2), suggesting a generalized monocyte activation. W e used how cytometry to demonstrate that HBP had a high affinity to mo nocytes but not to the LPS receptor CD14 and experiments performed at 4 degrees C indicated an energy-dependent step in this process. Confoc al microscopy showed that monocytes internalize HBP within 30 min., Th ese data suggest that mechanisms other than increased CD14 expression are responsible for tbe enhanced release of TNF-alpha or PGE(2) in res ponse to BBP and LPS.