Protective immune responses against Rhodococcus equi : an innate
immunity-focused review
Abstract
Rhodococcus equi causes pyogranulomatous pneumonia in foals and
immunocompromised people. Despite decades of research efforts, no
vaccine is available against this common cause of disease and death in
foals. The purpose of this narrative review was to summarize the current
understanding of interactions between R. equi and the host innate
immune system, to describe features of the immune response that are
associated with resistance or susceptibility to R. equi
infection, and help guide strategies for developing novel approaches for
preventing R. equi infections. Virulence of R. equi in
foals has been attributed to the virulence associated protein A which
allows intracellular survival in macrophages by preventing acidification
of R. equi-containing vacuole. Additionally, foal susceptibility
to R. equi infection is associated with immaturity and naivety of
innate and adaptive immune systems, while adult horses with fully
functional immune system are resistant to pneumonia. Specific
interaction between R. equi and innate immune cells can result in
bacterial survival or death; learning how to manipulate these responses
to control infection is critical to prevent pneumonia in foals.
Administration of live vaccines and stimulation of innate immune
responses appears to improve foals’ immune response and has the
potential to overcome the challenges of foal active vaccination and
elicit protection against pneumonia.