Foal Monocyte-Derived Dendritic Cells Become Activated uponRhodococcus equiInfection

Abstract

Susceptibility of foals to Rhodococcus equi pneumonia is exclusive to the first few months of life. The objective of this study was to investigate the immediate immunologic response of foal and adult horse antigen-presenting cells (APCs) upon infection with R. equi. We measured the activation of the antigen-presenting major histocompatibility complex (MHC) class II molecule, costimulatory molecules CD40 and CD86, the cytokine interleukin-12 (IL-12), and the transcriptional factor interferon regulatory factor 1 (IRF-1) in monocytederived macrophages (mMOs) and dendritic cells (mDCs) of adult horses and foals of different ages (from birth to 3 months of age) infected with virulent R. equi or its avirulent, plasmid-cured derivative. Infection with virulent or avirulent R. equi induced (P < 0.01) the expression of IL-12p35 and IL-12p40 mRNAs in foal mMOs and mDCs at different ages. This response was likely mediated by the higher (P ‫؍‬ 0.008) expression of IRF-1 in foal mDCs at birth than in adult horse mDCs. R. equi infection promoted comparable expression of costimulatory molecules CD86 and CD40 in foal and adult horse cells. The cytokine and costimulatory response by foal mDCs was not accompanied by robust MHC class II molecule expression. These data suggest that foal APCs detect the presence of R. equi and respond with the expression of the Th1-inducing cytokine IL-12. Nevertheless, there seems to be a limitation to MHC class II molecule expression which we hypothesize may compromise the efficient priming of naïve effector cells in early life.

Rhodococcus equi: Clinical Manifestations, Virulence, and Immunity

“…Activity of CTLs is improved by 6 weeks of age and is similar to that of adult horses by 8 weeks . Antigen‐presenting cells from foals have significantly lower CD1 and MHC class II expression compared to that from adult horses . In addition, several studies have demonstrated that the ability of equine lymphocytes and neutrophils to produce or upregulate various cytokines, or both, is strongly influenced by age .…”

Expression of interleukin-1β, interleukin-8, and interferon-γ in blood samples obtained from healthy and sick neonatal foals

“…On the basis of previous studies 15,20,21 to characterize cytokine profiles in PBMCs of healthy and sick foals, the β-actin gene was used as an internal reference gene to normalize the variation of cell numbers in the samples. On the basis of previous studies 15,20,21 to characterize cytokine profiles in PBMCs of healthy and sick foals, the β-actin gene was used as an internal reference gene to normalize the variation of cell numbers in the samples.…”

Rhodococcus equi pneumonia in foals: An assessment of the early diagnostic value of serum amyloid A and plasma fibrinogen concentrations in equine clinical practice

“…The disease typically manifests as a chronic pyogranulomatous inflammation in the form of broncopneumonia, enteritis and occasionally bacteremia and arthritis (Flaminio et al, 2009). Although many organisms can cause pneumonia in foals, infection with virulent Rhodococcus equi is considered to be the most common cause of severe pneumonia (Anon, 1978;Prescott, 1991;Takai et al, 1995).…”