TRANSGENIC MICE EXPRESSING A CHIMERIC ANTI-E-COLI IMMUNOGLOBULIN-ALPHA HEAVY-CHAIN GENE

To induce constitutive immunity against a pathogenic strain of Escherichia coli (K99), a rearranged immunoglobulin (Ig) heavy chain (HC) gene was constructed. Because the route of E. coli infection is enteric, an IgA transgene was desirable. A chimaeric gene construct was cloned that coded for a HC that recognized a specific E. coli pilus antigen. The construct comprised a kappa gene promoter, murine VDJ, and bovine alpha-HC constant region. Following microinjection of the HC construct into murine zygotes, of 50 liveborn mice, three were identified as transgenic. In all three transgenic founders, transgene-encoded mRNA expression was detected by northern blot. The transgenic founders were analysed for transgene-encoded RNA expression in splenic tissue before and after challenge with pathogenic E. coli. Founder 4-3 male expressed transgene-encoded RNA both before and after challenge; expression was detected in the other two founders only post-challenge. As no differences were found when sera were analysed for bovine IgA in control and transgenic mice, protein expression was assessed by challenge of HC founders with K99 E. coli by gavage. Control mice challenged with K99 E. coli were moribund within 24 h post-gavage, but there was no observable affect in the three transgenic founders. Unfortunately, after obtaining offspring from all founders, no transgenic offspring were identified (0/108). The low yield of transgenic founders, coupled with the apparent germ-line mosaicism may point to either mechanical or critical developmental anomalies. However, the production of transgenic mice harbouring an Ig HC gene construct confirmed that an Ig transgene coding for an antibody to an animal pathogen could function in a tissue-specific and protective manner in a mammalian system.