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.Aa heavy chain protein when infected with baculovirus that bore a construct that contained a honeybee melittin secretion (ms) signal attached to RT1.Aa cDNA. The RT1.Aa heavy chain protein in the culture supernatant and cell lysate immunoprecipitated in the presence of 5 individual anti-RT1.Aa-specific mAb. As was revealed by densitometric analysis, the ms signal increased the production (7- to 17-fold) and secretion (20- to 47-fold) of RT1.Aa protein by Sf9 cells (compared with RT1Aa-Sf9 cells without the ms signal). Subcutaneous immunization with secreted RT1.Aa heavy chain protein of Wistar-Furth (WF; RT1u) rats (day -4) accelerated the rejection of ACI (RT1a), but not third-party Brown Norway (BN; RT1n), heart allografts from 5.9 +/- 0.5 days in controls to 4.0 +/- 0.0 days (P < 0.001); cell lysate from RT1.Aa-Sf9 or ms/RT1.Aa-Sf9 cells reduced ACI heart allograft survival to 3.8 +/- 0.4 days or 3.7 +/- 0.5 days, respectively (P < 0.001). Indirect presentation of RT1.Aa heavy chain proteins by syngeneic macrophages shortened the survival of RT1.Aa-disparate PVG.R8 (RT1.AaDuBuCu) heart allografts in PVG.1U (RT1u) hosts from 6.3 +/- 0.5 days in controls to 4.0 +/- 0.0 days (P < 0.01). Finally, RT1.Aa heavy chain proteins injected into the thymus or into the portal vein (day -14) in combination with anti-T cell receptor mAb (days -14 and -13) induced indefinite survival of ACI liver allografts in Lewis (RT1l) recipients ( > 250 days). Thus, indirect presentation of soluble class I MHC heavy chain proteins (produced in a baculovirus/Sf9 cell system) may either sensitize or induce tolerance in the same fashion as native class I MHC alloantigens expressed on donor tissues.