Soluble rat MHC class I proteins induce accelerated rejection or prolonged survival of rat cardiac allografts

Soluble rat heavy chain class I major histocompatibility complex (MHC) proteins were produced by the use the use of an E. coli-based protein expression system. The proteins were purified by fast performance liquid chromatography (FPLC). Untreated Lewis(LEW, RT1.A^l) recipients rejected Brown-Norway (BN, RT1.Aⁿ) heart allografts at a mean survival time (MST) of 7.5±0.5 days, n=2. Subcutaneous (s.c.) immunization with 50 μg or 100 μg RT1.Aⁿ protein day -7 induced accelerated rejection of BN heart allografts at 5.0±0.0 days, (p<0.05, n =3) and 5.0±0.0 days, (p<0.05, n=3), respectively. This effect was not caused by bacterial contaminants because immunization of the LEW rats with self-RT1.A^l protein failed to induce accelerated rejection of BN allografts (MST 8.0±1.0 days; NS, n=2). In a tolerogenic protocol, 50 μg or 100 μg RT1.Aⁿ injected by portal vein (PV) at the time of transplantation to PVG rats plus a 7-day course of cyclosporine (CsA, 4 mg/kg/day) prolonged the survival of BN heart allograft to 25.8days±24.8 days, (13,13,13,20 and >80 days, p=0.05) and (15.0±5.0 days,p=0.05, n=2), respectively. Administration of RT1.Aⁿ protein alone produced MST of 9.75±0.25 days (n=4) or CsA alone a MST of 11.0±1.0 days, (n=3). These results document that the bacterial expression system may be used to produce in vivo active class I MHC immunogenic and tolerogenic proteins.