SHEEP PLASMA PROTEASE INHIBITORS INFLUENCING PROTEASE ACTIVITY AND GROWTH OF LUCILIA-CUPRINA LARVAE INVITRO

The enzyme inhibitors α2-macroglobulin (α2M), anti-thrombin III (AT III) and α1-proteinase inhibitor (α1PI) were isolated from sheep plasma and tested for their ability to affect L. cuprina larval proteases and larval growth in vitro. Casein radial diffusion gels indicated that both α2M and α1PI completely inhibited the protease activity of a larval excretory-secretory preparation, while AT III had a partial effect. Casein zymograms revealed that α2M inhibited all of the larval proteases, while AT III was able to modify the normal plaque pattern; α1PI inhibited all plaques except a doublet present at pI 8.5. Larval growth in vitro was significantly inhibited by α2M and AT III (P < 0.05) when compared to albumin controls but was not affected by α1PI. The levels of α2M in sheep serum were monitored over the course of a larval fly infection. A significant increase in α2M (P < 0.05) was recorded in the serum of flystruck sheep. It is suggested that, under certain circumstances, these inhibitors may be involved in influencing flystrike through reducing the activity of larval proteases necessary for wound formation and larval nutrition. © 1990.