Abstract
An in vitro porcine bone marrow-derived dendritic cell (DC) culture was developed as a model for evaluating immune polarization induced by adjuvants when administered with immunogens that may become vaccine candidates if appropriately formulated. The swine pathogen Streptococcus suis was chosen as a prototype to evaluate proposed S. suis vaccine candidates in combination with the adjuvants Poly I:C, Quil A ®, Alhydrogel ®, TiterMax Gold ® and Stimune ®. The toll-like receptor ligand Poly I:C and the saponin Quil A ® polarized swine DC cytokines towards a type 1 phenotype, with preferential production of IL-12 and TNF-α. The water-in-oil adjuvants TiterMax Gold ® and Stimune ® favoured a type 2 profile as suggested by a marked IL-6 release. In contrast, Alhydrogel ® induced a type 1/type 2 mixed cytokine profile. The antigen type differently modified the magnitude of the adjuvant effect, but overall polarization was preserved. This is the first comparative report on swine DC immune activation by different adjuvants. Although further swine immunization studies would be required to better characterize the induced responses, the herein proposed in vitro model is a promising approach that helps assessing behaviour of the vaccine formulation rapidly at the pre-screening stage and will certainly reduce numbers of animals used while advancing vaccinology science.
Highlights
Streptococcus suis is an encapsulated bacterium and an important cause of disease in swine, including meningitis, septicemia with sudden death, endocarditis and arthritis
Expression of cell surface markers of swine bone marrow-derived dendritic cell (bmDC) was assessed by FACS after eight days of culture with the in house-produced porcine granulocyte-macrophage colony-stimulating factor supernatant in comparison to commercial swine recombinant (r)GM-CSF (Table 1)
No significant differences were observed in bmDC phenotype obtained by culturing in the presence of in house-prepared porcine granulocyte-macrophage colony-stimulating factor (pGM-CSF) compared to that obtained when using commercial rGM-CSF (Table 1)
Summary
Streptococcus suis is an encapsulated bacterium and an important cause of disease in swine, including meningitis, septicemia with sudden death, endocarditis and arthritis. S. suis was originally classified into 35 serotypes based on the capsular polysaccharide (CPS) antigenicity, the current taxonomical situation has been recently revised [3]. The main port of entry for S. suis is the upper respiratory tract [7]. This pathogen can overthrow the immune system, through an arsenal of virulence factors, including the CPS [8], to cause acute septicemia that may lead to septic shock or different clinical outcomes depending on the colonized organ via mechanisms that are only partially elucidated to date [9]
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