Natural and immune antibodies for Vibrio fetus in serum and secretions of cattle.

Naturally occurring antibodies for Vibrio fetus with whole-cell and O antigen specificities were detected in sera of mature cattle by means of the agglutination and indirect immunofluorescence reactions. O antibodies occurred in each of 21 sera examined, and whole-cell antibodies, in lower concentrations, occurred in 15 of the 21 sera. Natural antibodies were detected in the immunoglobulin G, M, and A (IgG, IgM, IgA) classes. Parenteral immunization with whole cells in Freund's complete adjuvant caused an increase in antibodies, predominantly IgG, with both whole-cell and O specificities; genital infection produced minimal alterations in levels of serum antibody. O antibodies, predominantly of the IgA class, occurred in nasal secretions of most of these animals but only infrequently in saliva or tears. Nasal secretion titers of O antibodies fluctuated widely from week to week but appeared to be unaffected by parenteral immunization or experimental infection. It is hypothesized that the nasal passages serve as a site of antigenic stimulation and synthesis of naturally occurring V. fetus antibodies.