IMMUNOHISTOLOGICAL CHARACTERIZATION OF THE LOCAL CELLULAR-RESPONSE DIRECTED AGAINST PSEUDORABIES VIRUS IN PIGS

The aim of this study was to investigate the kinetics of a primary and secondary immune response against pseudorabies virus (PRV). Pigs vacc inated with strain 783 and unvaccinated pigs were challenged with wild -type PRV by either intranasal or subcutaneous infection. Non-challeng ed pigs were used as controls. On days 1, 3 and 7 after challenge, tis sues from the site of infection, and the tonsils of intranasally and t he draining lymph nodes of subcutaneously challenged pigs were sampled . Immunohistological staining was used to characterize the various cel l populations at the primary site of virus replication and in the lymp hoid tissue. Tissue sections were stained for the T-cell markers CD2, CD3 gamma delta, CD4 and CD8, for the B-cell markers IgM, IgA and IgG, for a macrophage marker, and for PRV antigen. After challenge, PRV wa s detected during a shorter period in vaccinated pigs, and was less di sseminated than in unvaccinated pigs. Cellular infiltrates were detect ed both in the nasal mucosa and the subcutaneous tissue of both unvacc inated and vaccinated pigs. Cell infiltrates, however, appeared earlie r in vaccinated than in unvaccinated pigs, indicating a difference in kinetics of the primary and secondary immune response. The appearance of T-cells preceded the appearance of B-cells, bur the proportion of t he various subsets did not differ between unvaccinated and vaccinated pies. These findings suggest that the early immune response in vaccina ted pigs may contribute to the rapid clearance of virus at the primary sire of infection. In addition, T-cells appear to have a more importa nt role in the clearance of PRV than B-cells. (C) 1997 Elsevier Scienc e B.V.