Characterization of the antibody response in inbred mice to a high-molecular-weight polysaccharide from Pseudomonas aeruginosa immunotype 1

We explored the genetic basis for the differing immune responses observed in inbred strains of mice to a high-molecular-weight polysaccharide (PS) from Pseudomonas aeruginosa immunotype 1 (IT-1). Previous studies have shown that C3H mice immunized with this antigen produce only immunotype-specific antibody. BALB/c mice immunized with IT-1 PS produce both anti-IT-1 PS antibody and antibody cross-reactive with PS from P. aeruginosa immunotype 2 (IT-2). In the current study, we observed that, in addition, these two strains differ in their ability to respond to low immunizing doses of IT-1 PS. C3H mice generated a protective antibody response after a 1-μg immunization, whereas BALB/c mice failed to produce protective antibody after receiving 1 μg of PS. Both strains generated protective levels of antibody after a 50-μg immunization. Genetic analysis of these response patterns indicates that the ability to produce cross-reactive antibody and the ability to respond to a 1-μg immunization are independently inherited traits. In addition, the responsiveness of C3H mice to a 1-μg immunization with the production of protective levels of antibody is not linked to the mouse major histocompatibility (H-2) complex, to sex-linked genes, or to a single gene outside the H-2 complex.