Distribution of specific antibody activity among serum immunoglobulin isotypes following bovine herpesvirus I infection of cattle

The kinetics of antibody formation in Holstein-Friesan heifers following primary and secondary intranasal inoculation of bovine herpesvirus I (BHVI), reactivation of latent BHVl (RLI), and BHVI-induced abortion was determined. Sera were fractionated by gel filtration and ion exchange chromatography. The antibody activity within serum immunoglobulin isotypes was assessed by a virus plaque reduction assay (PRA).

The primary immune response to BHVl infection was characterized by the appearance of IgM and IgG antibodies in serum 7 days post inoculation (pi). Maximal IgG antibody activity occurred at 35 day pi in nonpregnant heifers and 14 days pi in pregnant heifers. Thereafter antibody activity in this class slowly declined. Maximal IgM antibody activity occurred at 14 days pi in both groups of heifers and declined rapidly thereafter. The IgG antibody activity during primary immune responses was localized to the IgG1 subclass primarily.

Secondary responses were characterized by anamnestic IgG antibody responses. Secondary IgM antibody formation was elicited by abortion induced by the intraamniotic inoculation of BHVI and RLI, but not by reexposure by the intranasal route. Antibody activity was present within both IgG subclasses during secondary immune responses. However, the increase in antibody activity during this period was in the IgG2 subclass primarily.

Abortion occurred in one heifer 28 days after intranasal BHVI inoculation. Abortion in this animal failed to stimulate a secondary antibody response.

The nature of BHVI antigenic exposure in the bovine was determined by assessing the relative distribution of anti-BHVI antibody activity among the serum immunoglobulin isotypes, IgM, IgGl, and IgG2. The formation of IgM antibody, with the exception of secondary intranasal exposure, indicated recent BHVI antigenic exposure. Primary immune responses were differentiated from secondary immune responses by the presence of IgGl antibody and the absence of IgG2 antibody.