INDUCTION OF SPECIFIC ALLOGRAFT IMMUNITY BY SOLUBLE CLASS-I MHC HEAVY-CHAIN PROTEIN PRODUCED IN A BACULOVIRUS EXPRESSION SYSTEM

Spodoptera Frugiperda (Sf9) insect cells secreted a class I MHC RT1.A( a) heavy chain protein when infected with baculovirus that bore a cons truct that contained a honeybee melittin secretion (ms) signal attache d to RT1.A(a) cDNA. The RT1.A(a) heavy chain protein in the culture su pernatant and cell lysate immunoprecipitated in the presence of 5 indi vidual anti-RT1.A(a)-specific mAb. As was revealed by densitometric an alysis, the ms signal increased the production (7- to 17-fold) and sec retion (20- to 47-fold) of RT1.A(a) protein by Sf9 cells (compared wit h RT1A(a)- Sf9 cells without the ms signal). Subcutaneous immunization with secreted RT1.A(a) heavy chain proteins of Wistar-Furth (WF;RT1(u )) rats (day -4) accelerated the rejection of ACI (RT1(a)), but not th ird-party Brown Norway (BN;RT1(n)), heart allografts from 5.9+/-0.5 da ys in controls to 4.0+/-0.0 days (P<0.001); cell lysate from RT1.A(a)- Sf9 or ms/RT1.A(a)-Sf9 cells reduced ACI heart allograft survival to 3 .8+/-0.4 days or 3.7+/-O.5 days, respectively (P<0.001). Indirect pres entation of RT1.A(a) heavy chain proteins by syngeneic macrophages sho rtened the survival of RT1.A(a)-disparate PVG.RS (RT1.A(a)D(u)B(u)C(u) ) heart allografts in PVG.1U (RT1(u)) hosts from 6.3+/-0.5 days in con trols to 4.0+/-0.0 days (P<0.01). Finally, RT1.A(a) heavy chain protei ns injected into the thymus or into the portal vein (day -14) in combi nation with anti-T cell receptor mAb (days -14 and -13) induced indefi nite survival of ACI liver allografts in Lewis (RT1(1)) recipients (>2 50 days). Thus, indirect presentation of soluble class I MHC heavy cha in proteins (produced in a baculovirus/Sf9 cell system) may either sen sitize or induce tolerance in the same fashion as native class I MHC a lloantigens expressed on donor tissues.