Effect of Cycloheximide and of Anti-C3 Fab' on the Intrinsic Synthesis and Secretion of Lysosomal Enzyme and of Complement Components by Guinea-pig Peritoneal Macrophages

Without any additional stimulus, the lysosomal enzyme N-acetyl-beta-D-glucosaminidase (beta-GLU) is secreted immediately from starch gel induced guinea-pig peritoneal macrophages. A more than three-fold increase of the total enzyme activity in the course of 3 days and the reversible inhibition of this enzyme increase by cycloheximide prove the synthesis of beta-GLU. The synthesis rate of beta-GLU remains rather constant after the second day, despite rapid cell death in the same culture period which could be explained by heterogeneity of the macrophage population. Cycloheximide immediately inhibits secretion of C3 whereas inhibition of beta-GLU secretion is only observed after a lag phase of 24 h. Secretion of factor D and of beta-GLU is not altered if secreted C3 is totally neutralized by the addition of anti-C3 Fab' to macrophage cultures. Thus, endogenous C3 as well as its endogenously generated fragments do not influence these macrophage functions. In the same cultures with anti-C3 Fab', conversion of secreted factor B into its fragments is inhibited as indicated by the detection of functional B activity. These results indicate that the secretion of factor D and of beta-GLU is also independent of endogenous B-derived fragments such as Bb. Finally, the detection of functional B in cultures with anti-C3 Fab' proves that C3b is required for factor B activation. The apparent interaction of secreted C3 and factors D and B in regular macrophage cultures suggests the constant formation of the labile C3 convertase C3bBb of the alternative pathway.