Innate Immune Responses to a Saponin Adjuvant in the Pig Application of Gene Expression Profiling

Vaccination is one of the most powerful ways to prevent infectious diseases. Successful vaccines produce a long-term immunity including effector T and B lymphocytes. In this context, adjuvants have a key role in vaccines by stimulating the innate immunity and thereby enhancing and shaping the subsequent adaptive immune response. The aim of this thesis was to elucidate the early innate immune response to the saponin-based adjuvant Matrix-M in the pig. Gene expression profiling was applied to monitor the global transcriptional response to Matrix-M in vivo. The innate immune response was further characterized by quantitative PCR analysis in vivo and in vitro and the early immunomodulatory effect of Matrix-M was evaluated in a contact exposure model. A mild inflammation and a cellular influx were recorded at the injection site and in the draining lymph node 24 hours after intramuscular injection of Matrix-M in pigs. In accordance, microarray analysis detected transcriptional alterations of genes for cytokines, chemokines and pattern recognition receptors in both tissues. Interferonregulated genes were significantly overrepresented in these tissues, accompanied by increased gene expression for interferon-β in in the draining lymph node and interferon-α in blood. Transcriptional responses to Matrix-M in vitro were generally low but increased culture and exposure time affected genes for pro-inflammatory cytokines and TH cytokines in lymphocytes. Low levels of interferon-α gene expression were also detected in monocyte-derived dendritic cells. A contact exposure model was established to mimic field conditions when allocating grower pigs, by mixing pigs of various health statuses. After transport and mixing with conventionally reared pigs, all specific pathogen free (SPF) pigs in this model developed respiratory disease. Systemic symptoms that correlated with granulocyte counts, serum amyloid A levels and transcription of IL18 and TLR2 were provoked in two out of four SPF pigs that received saline prior to exposure, but not in those given Matrix-M. Taken together, the application of gene expression profiling successfully identified the induction of innate immune responses in porcine tissues and indicated that Matrix-M primes the host for further immune regulation. Thus, Matrix-M or similar saponin formulations are potentially useful clinical immunomodulators or adjuvants in emergency vaccines.