RÉSUMÉ
The isotype distribution of antibody (Ab) responses to Salmonella antigens (Ag) was investigated in high (H) and low (L) Ab responder lines of mice from Selections III and carried out for responsiveness to flagellar (f) and somatic (s) Ag, respectively. Primary immuniztion resulted in higher Ab titers of all isotypes in response to both Ag in H mice fro m both selections and was confirmed after booster injections. The interline difference (H-L) in response to the distinct isotypes ranged from 3.0 to 7.0 log2 to Ag f in Selection III and from 2.0 to 5.1 log2 to Ag s in Selection IV. Comparison of isotype production to 3 Ag in Selections I,II,III and IV demonstrated that: 1) the highest responses in all mice are those against the selection Ag, 2) the isotypic pattern depends on both the Ag injected and the host's genetic constitution, and 3) the presence or lack of a multispecific effect is not due to isotype-restricted regulation