Innate immunity is an ancient system that prevents microbial infection in all animals, from worms to
humans. In the face of daily exposure to potential pathogens, vertebrates use this system to prevent
opportunistic infections such as invasive candidiasis through coordinated activities of barrier tissues and
professional innate immune phagocytes. Deficiencies in neutrophils or barrier breaches predispose for lethal
invasive candidiasis, the fourth most common nosocomial infection. Thus, understanding of Candida
interaction with these host cells at mucosal surfaces promises to elucidate aspects of mucosal candidiasis and
may reveal how this non-lethal disease progresses to invasive candidiasis.
While simplified in vitro studies have revealed how C. albicans can interact with epithelial cells and
phagocytes, these in vitro interactions result in epithelial destruction rather than the containment usually seen
in vivo. Thus, it is important to study C. albicans-barrier interactions in vivo to understand how phagocytes
normally collaborate with the epithelium to prevent invasive candidiasis in vivo. The transparent zebrafish
infection models we have developed enable us to study these events at high resolution within the
complex natural environment of the intact host.
Our objective here is to use intravital imaging to determine how innate and epithelial immune response in
vivo impacts epithelial invasion, a key aspect of C. albicans pathogenesis. We propose to test the hypothesis
that phagocyte recruitment and epithelial barrier integrity block invasive hyphal growth of C. albicans.
Our own preliminary data, combined with work from others, implicate neutrophils in blocking filamentous
growth and mucosal tissue invasion. In Aim 1, we will capitalize on these preliminary results to discover how
neutrophils directly target C. albicans, how their activity is modulated by chemokine signaling, and examine
how other immune responses are altered in their absence. Published work implicates active epithelial
responses in barrier protection, and our preliminary data has identified an epithelial receptor required for
protection. In Aim 2, we will focus on this receptor to determine how epithelial signaling assists in immunity,
examining its roles in immune response and epithelial organization during infection.
The long-term rationale for the proposed research is that intravital imaging of host-C. albicans dynamics
in vivo will generate more complete models for fungal-innate immune dynamics during infection that may lead
to more rational therapeutic approaches. The transparent zebrafish model of mucosal candidiasis offers a
unique opportunity to characterize complex dialog that coordinates anti-fungal defense at this barrier. The
proposed experiments are expected to reveal how neutrophil attack (Aim 1) and epithelial signaling (Aim 2)
prevent C. albicans invasion of the mucosal epithelium, a crucial event in its pathogenesis.