Expression of Endopeptidase‐24.11 (Common Acute Lymphoblastic Leukaemia Antigen CDI0) in the Sciatic Nerve of the Adult Rat After Lesion and During Regeneration

Endopeptidase‐24.11, which is identical with the common acute lymphoblastic leukaemia antigen CD1O (CALLA), is a cell surface Zn²⁺ metalloprotease that regulates peptide‐induced responses in different tissues, including the nervous and immune systems. In the peripheral nervous system, high levels of the enzyme are present in all neonatal and early postnatal Schwann cells, while as myelination proceeds it is gradually suppressed in the majority of cells that form myelin but retained in non‐myelin‐forming cells in the adult animal. In the present study we have investigated the effects of transection, crush and regeneration of the adult rat sciatic nerve on the expression of the endopeptidase by Schwann cells in situ. Endopeptidase‐24.11 was monitored by immunocytochemistry using the monoclonal anti‐endopeptidase antibody 23811. For comparison, a parallel study was carried out with a monoclonal antibody directed against the rat nerve growth factor receptor. We found that (i) all Schwann cells of the distal segment re‐expressed endopeptidase‐24.11 as early as 4 days after axotomy, the level of immunostaining reaching a maximum after 2 weeks, (ii) axonal regeneration repressed Schwann cell expression of endopeptidase‐24.11, and (iii) the induction of the nerve growth factor receptor followed a similar pattern to that of endopeptidase‐24.11 in the transected and crushed nerve. Enzymatic amplification of endopeptidase‐24.11 cDNA from normal and axotomized adult rat sciatic nerve confirmed the expression of endopeptidase‐24.11 in these tissues. Our results show that the expression of endopeptidase‐24.11 in Schwann cells, as is the case with the nerve growth factor receptor, is induced by the loss of the normal axon‐Schwann cell contact. The significant increase in the expression of endopeptidase‐24.11 by Schwann cells after axonal damage suggests that the enzyme could play a role in axonal regeneration.