Five murine epitopes were defined and mapped within IgA1 protease produced by 
Neisseria meningitidis. Epitopes 1 and 2 were present in IgA1 protease from all 
strains, and from Neisseria gonorrhoeae. Epitopes 3 through to 5 varied between 
subgroups of serogroup A meningococci, but have remained constant over decades 
within the subgroups, except for epitope 4, which changed between 1983 and 1987 
during the spread of subgroup III meningococci from Asia to Africa. Binding of 
monoclonal antibodies to epitopes 1, 4 and 5 neutralized enzymatic function. 
Human sera containing antibodies to IgA1 protease as a result of natural 
infection inhibited binding of monoclonal antibodies to epitope 4 but not to the 
other epitopes.