Disease vs Immunization" e.g. Brucella

[John Cherwonogrodzky]

Dear Colleagues:
     There's an interesting discussion on disease vs immunization which seems 
to be focusing on the similarities. As this is an immunology net, I'd like to 
add a few comments on immunological differences between vaccination and 
immunization, using Brucella as an example.
     In cattle populations, animals are immunized with an attenuated strain 
(B. abortus strain 19). In the 1970s-early 1980s, a Spanish/American team 
found there was a compound from Brucella that can differentiate vaccinated 
from infected animals. In the 1980s, a Canadian team found this was purified 
O-polysaccharide (OPS). Purified OPS is recognized by infected animal 
antibodies when this antigen is used either in immunodiffusion plates or in 
ELISAs, when the OPS is part of lipopolysaccharide (LPS) it is recognized by 
both vaccinate and infected cattle sera. Monoclonal antibody studies suggest 
that this recognition has little to do with antibody isotype. 
     The mechanism of the above is believed to be that when an animal is 
vaccinated, its immune system gets only a quick look at the "tip" part of the 
outer layer of OPS, when the animal is infected it has the opportunity for a 
long look at the antigens and forms antibodies to the "length" epitopes of the 
OPS. 
    The above suggests that there are immunological differences between 
disease (infection) and immunization (vaccination).
     Take care...John