Abolition of resistance to Klebsiella pneumoniae by anti-polymorphonuclear leucocyte IgG.

Antipolymorphonuclear leucocyte IgG (APS IgG) was prepared from crude horse antipolymorphonuclear leucocyte antiserum (APS). The APS IgG was less toxic than the crude APS and had a powerful and specific effect on rabbit polymorphs in vivo and in vitro. In rabbits infected with Klebsiella pneumoniae it suppressed the normal polymorph response and greatly reduced resistance to infection. Anti-Klebsiella pneumoniae antibody greatly enhanced protection in normal rabbits, but had much less effect on APS/IgG-treated rabbits. It was concluded that the principal cellular defence against K. pneumoniae was the polymorph and that macrophages made only a relatively small contribution to resistance.