Biology Reference
In-Depth Information
Although PRV has been widely studied (especially its agricultural impact, its viral
pathogenesis, its molecular biology, its use as a neuronal tracer, and in DNA vaccine
exploration [1]) how the native host responds globally after infection with wild type
PRV is still poorly understood. Clinically, infection in older pigs ranges from asymp-
tomatic to severe respiratory disease but with limited mortality. Young piglets exhibit
more serious clinical signs and often succumb to fatal encephalitis preceded by typical
behaviors consistent with infection of the CNS. In recent years, microarray technology
has proven useful to assess the cellular transcriptional responses to herpesvirus infec-
tions in human and mouse cell lines [3-5]. It has been used to study host gene expres-
sion after PRV infection of rat embryo fi broblasts [5], and the CNS in rodent brain at
various times post infection
in vivo
[6]. However few porcine genome-wide expres-
sion studies have been published. Most experiments have used “in-house” cDNA ar-
rays to study transcriptional events in pig tissues, such as the stress-genes related to
early weaning of piglets [7]. The down side of these cDNA-based clone libraries is that
the genes represented on the array are often very focused on a given biological system
or process and lack a whole genome overview.
In this study, piglet samples were hybridized onto an Illumina Human Refset Chip
(Illumina Inc. San Diego), corresponding to 23,000 transcript probes. This cross-spe-
cies comparison potentially allows the study of the whole transcriptome. There are
now porcine arrays available from commercial suppliers (e.g., Affymetrix and Qia-
gen), but these are not all representative of the entire pig genome and were not widely
available at the time of this study. In the absence of a comprehensive species-specifi c
array deeper interrogation of the pig gene complement was afforded by the use of the
better annotated human geneset. Although the use of this approach can only be par-
tially informative when there are no confi rmed pig orthologs in the public databases,
we have identifi ed host cellular genes whose mRNA levels change during natural PRV
infection of piglet brain and lung. The resulting data defi ne key pathways of
host
-gene
expression that characterize the host response to an acute CNS and respiratory infection.
MATERIALS AND METHODS
Experimental Pigs and Housing
The experimental animals were sourced from an outbreak of PRV that occurred in the
farrowing house of a local commercial farmer due to a reduced level of protection via
maternal antibody. Clinical signs were described as follows: suckling piglets were
listless, febrile, and uninterested in nursing. Within 24 hr of exhibiting these clinical
signs, some piglets progressively developed indications of CNS infection including
trembling, excessive salivation, lack of coordination, ataxia, and seizures. Infected
piglets sat on their haunches in a “dog-like” position, lay recumbent and paddled, or
walked in circles. The appearance of the dissected organs in selected piglets was typi-
cal of PRV infection: bleeding in meninges, oedema in the brain, bleeding spots in the
lung, and on the adenoids [1, 8].
Three strict criteria were imposed for the selection of piglets included in this study:
(1) piglets exhibited the typical clinical signs described above; (2) piglets exhibited the
expected pathology, especially in brain, and lung; (3) virus isolation, antibody identi-
