<a href="https://en.wikipedia.org/wiki/Lloyd_J._Old" id="mwAWM" rel="mw:WikiLink" title="Lloyd J. Old">Lloyd J. Old</a> identified the first <a href="https://en.wikipedia.org/wiki/Cell_membrane" id="mwAWQ" rel="mw:WikiLink" title="Cell membrane">cell surface</a> <a href="https://en.wikipedia.org/wiki/Antigen" id="mwAWU" rel="mw:WikiLink" title="Antigen">antigens</a> that could differentiate among different <a href="https://en.wikipedia.org/wiki/Cell_type" id="mwAWY" rel="mw:WikiLink" title="Cell type">cell types</a>.