An immunohistochemical study of phospholipase A2 in peripheral nerve during Wallerian degeneration.

Antiserum raised against purified Crotalus adamanteus venom phospholipase A2 (PLA2) was used to localise the enzyme in normal and crushed sciatic nerve to determine the effect of nerve trauma on PLA2 distribution in the PNS. The tissue was Bouin's fixed, and stained immunohistochemically using the Vectastain ABC technique. Anti-PLA2 antiserum showed weak reactivity with normal rat myelin, while only 'resident' macrophages stained in normal mouse sciatic nerve. Post-crush, in the mouse, myelin staining was localised close to the crush site, with strong lysosomal staining within both 'resident' and invading haematogenously derived macrophages. In the rat, myelin sheaths stained strongly throughout the nerve very soon after crush, but no macrophages were detected using these antisera. Paranodal myelin and some Schmidt-Lanterman incisures were the first regions of the sheath to show an increase in PLA2 staining post-crush, areas where the first ultrastructural changes occur in myelin after trauma, with staining of compact myelin closely following. Our findings support the idea that PLA2 may be involved in the early process of myelin breakdown seen in Wallerian degeneration.