To determine the amount of plasminogen in microglial conditioned medium, a highly sensitive and specific enzyme-linked immunosorbent assay (ELISA) for rat plasminogen was established. Weak cross-reactivity with human serum plasminogen was observed, while no reactivity was detected with frog and carp plasminogen. The specificity of the immunosorbent assay was confirmed by Western blotting. The secretion of plasminogen into the microglial culture medium was quantified by using the established ELISA and was found to be increased depending on the culture time and number of microglia. The secretion was increased about 5-fold by stimulation with retinoic acid, while interleukin-1, and basic fibroblast growth factor showed no significant effect.
