Issue |
Vet. Res.
Volume 31, Number 1, January-February 2000
|
|
---|---|---|
Page(s) | 135 - 135 | |
DOI | https://doi.org/10.1051/vetres:2000063 | |
How to cite this article | Vet. Res. (2000) 135-135 |
Analysis of protective immunity against PRV infection in pigs using attenuated and inactivated PRV vaccines
E.M.A. van Rooij, M.G.M. de Bruin, Y.E. de Visser, W. Boersma and A.T.J. BianchiDepartments of Mammalian Virology and Immunology, Institute for Animal Science and Health, ID-DLO, Lelystad, The Netherlands
Abstract -
Knowledge on the immune mechanisms of
protective immunity against Pseudorabies virus (PRV) infections in pigs is essential for the
development of new, biologically safe vaccines. To evaluate the role of
different immune mechanisms in relation to protection, we studied the humoral and
cell-mediated immune responses in pigs after vaccination with attenuated
or inactivated PRV vaccines and after challenge infection with wild type PRV. In addition, we
also studied the role of the adjuvant component in the induction of
protective immunity. Groups of 10-12 week old SPF pigs were intramuscularly vaccinated twice,
with an interval of 4 weeks. All vaccines were based on the Bartha strain.
Group 1 received the modified live vaccine in o/w adjuvant (MLV +A), group 2 the modified
live vaccine without adjuvant (MLV), group 3 the inactivated vaccine
with o/w adjuvant (IV +A) and group 4 the inactivated vaccine without adjuvant (IV). Group 5
was sham-vaccinated with PBS. Six weeks after the second vaccination,
all pigs were intranasally challenged
with
105 plaque forming units of the virulent wild type
PRV strain NIA3 per animal to assess the protection. The animals were
screened for humoral and cellular immune responses, including Facscan analysis of the
proliferating cell compartment at regular intervals after vaccination
and challenge infection. Virus excretion, body weight, fever and clinical signs were assessed
after challenge infection. Pigs vaccinated with MLV +A, MLV or IV +A
induced high levels of neutralising antibodies in pigs whereas pigs vaccinated with IV
developed significantly lower levels of VN antibody titers. Pigs
vaccinated with MLV +A developed the strongest lymphoproliferation (LPT) responses followed
by pigs vaccinated with MLV. In contrast, pigs vaccinated with inactivated
vaccines developed weak LPT (IV +A) or very weak (IV) LPT responses. The analysis of the
proliferating cell compartment showed that MLV +A vaccinated pigs had
significantly more CD4
+/CD8
/CD6
+
blast cells than the other groups of pigs, and
significantly more CD4
-/CD8
/CD6
+ blast cells than the IV +A, IV
and sham vaccinated pigs. After challenge infection, MLV +A vaccinated pigs were protected
the best followed by MLV vaccinated pigs, as illustrated by the reduction
of virus excretion. Although pre-challenge VN antibody levels of IV +A vaccinated pigs were
comparable with antibody levels of MLV (+ or -A) vaccinated pigs, IV +A pigs
were less protected during the first week after challenge infection. Moreover, although
antibody levels between pigs vaccinated with IV +A and IV differed significantly,
both groups of pigs were equally poorly protected, confirming the lack of correlation between
VN antibody titres and early reduction in virus excretion. After challenge
infection, pigs vaccinated with MLV+A showed strongest LPT responses with high numbers of
both CD4
+/CD8
/CD6
+ and
CD4
-/CD8
/CD6
+ blast cells at day 3 post-challenge.
Pigs vaccinated with MLV showed intermediate LPT responses with high numbers of
CD4
-/CD8
/CD6
+
blast cells whereas pigs vaccinated with IV+A showed weak LPT
responses with high numbers of CD4
+/CD8
/CD6
+
blast cells. These data indicate that
protection and early reduction in virus excretion is not related to VN antibody
titers but to the strength of LPT responses,
further characterised by high numbers of both
CD4
+/CD8
/CD6
+
and CD4
-/CD8
/CD6
+
cell subsets. The use of the o/w adjuvant
led to stronger antibody and stronger LPT
responses after vaccination with MLV and IV with an
increase of the CD4
+/CD8
/CD6
+ blast cell population.
Corresponding author: E.M.A. van Rooij Fax: (31) 320 238668;
e-mail: e.m.a.vanrooij@id.dlo.nl
© INRA, EDP Sciences 2000