\ifdefined\directlua\input luaotfload.sty\fi
\font\iwona           =iwona      at 20pt
\font\iwonabold       =iwona/b    at 20pt
\font\iwonaitalic     =iwona/i    at 20pt
\font\iwonabolditalic =iwona/bi   at 20pt

\def\test{foo bar baz \endgraf}
{\iwona           \test}
{\iwonabold       \test}
{\iwonaitalic     \test}
{\iwonabolditalic \test}
\bye