Abstract
Feline calicivirus (FCV) is a common cat virus associated with oral ulcerations and virulent-systemic disease. Efficacious FCV vaccines protect against severe disease but not against infection. The high genetic diversity of FCV poses a challenge in vaccine design. Protection against FCV has been related to humoral and cellular immunity; the latter has not been studied in detail. This study investigates the cellular and humoral immune response of specified pathogen-free (SPF) cats after modified-live FCV F9 vaccinations and two heterologous FCV challenges by the analysis of lymphocyte subsets, cytokine mRNA transcription levels, interferon (IFN)-γ release assays in peripheral blood mononuclear cells (PBMCs), anti-FCV antibodies, and neutralisation activity. Vaccinated cats developed a Th1 cytokine response after vaccination. Vaccination resulted in antibodies with neutralising activity against the vaccine but not the challenge viruses. Remarkably, IFN-γ-releasing PBMCs were detected in vaccinated cats upon stimulation with the vaccine strain and the first heterologous FCV challenge strain. After the first experimental infection, the mRNA transcription levels of perforin, granzyme B, INF-γ, and antiviral factor MX1 and the number of IFN-γ-releasing PBMCs when stimulated with the first challenge virus were higher in vaccinated cats compared to control cats. The first FCV challenge induced crossneutralising antibodies in all cats against the second challenge virus. Before the second challenge, vaccinated cats had a higher number of IFN-γ-releasing PBMCs when stimulated with the second challenge virus than control cats. After the second FCV challenge, there were less significant differences detected between the groups regarding lymphocyte subsets and cytokine mRNA transcription levels. In conclusion, modified-live FCV vaccination induced cellular but not humoral crossimmunity in SPF cats; innate immune mechanisms, secretory and membranolytic pathways, and IFN-γ-releasing PBMCs seem to be important in the host immune defence against FCV.
Highlights
Feline calicivirus (FCV) is one of the most common viral pathogens in cats worldwide [1]
The magnitude of the humoral immune response induced by FCV F9 vaccination was highly variable between individuals, and, in the absence of maternal antibodies, high antibody titres were detected in some cats after a single FCV F9 vaccine injection
A Th1-directed immune response was elicited in cats vaccinated with the FCV F9 vaccine
Summary
FCV is one of the most common viral pathogens in cats worldwide [1]. FCV prevalence can range from low to high (10–90%) [2,3,4,5,6,7], depending on the population sampled, but multicat situations, such as in shelters or breeding catteries, are especially of concern. Two types of FCV vaccines are mainly used in Europe: (1) A modified-live single-strain vaccine containing FCV F9 or (2) an inactivated double-strain vaccine containing FCV 431 and FCV G1. Both types of FCV vaccines do not induce sterilising immunity but rather reduce the severity of clinical signs if cats are affected by a classical FCV disease [13]. The protection of cats lacking neutralising antibodies implies an important role for cellular immunity in FCV infection. A comprehensive study on the humoral and cellular immune response of cats after FCV F9 vaccination and after two subsequent experimental FCV infections with recently collected field strains is lacking
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