Protection by monospecific gonococcal antisera of the chicken embryo challenged with Neisseria gonorrhoeae.

The protective effects of monospecific gonococcal antisera on 11-day chick embryos challenged with a known lethal dose of gonococci were assessed. The monospecific antisera were prepared by immunisation of rabbits with purified gonococcal antigens, and removal of trace amounts of unwanted antibodies was achieved by absorption with antigen covalently bound to cyanogen bromide-activated Sepharose beads. The antisera were standardised for IgG by solid-phase radioimmunoassay. Antiserum raised against whole outer membrane was protective and antiserum raised against the lipopolysaccharide (LPS) was moderately protective. Outer-membrane antiserum from which the LPS component was removed by absorption was less protective than either of these sera. Investigation of the protective mechanism of anti-LPS antibodies indicated that in addition to any antitoxic effect, these antibodies inhibited the multiplication of gonococci. Antisera raised against individual outer-membrane proteins offered no protection in this test. Out of five antisera tested, antipilus serum gave the strongest protection when piliate gonococci were used as the challenge in this model; antipilus serum did not protect against challenge with non-piliate gonococci.