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Equine January/February 2009 (Vol 4, No 1)

News Bits (January/February 2009)

by Stacey Oke

    Two separate research groups that focused on the genetic factors that affect a horse's immune response to diseases (e.g., Rhodococcus equi infection) have generated data indicating that interleukin (IL)-1β (or an IL-1β-related pathway) plays an important role. To date, a number of cytokines that are thought to play an important role in inflammation and regulation of the immune system have been identified. These cytokines include Toll-like receptors and galectin-3.

    R. equi—an important cause of severe, purulent pneumonia in young horses and immunocompromised humans—is a facultative intracellular pathogen that is able to resist phagocytosis by host macrophages. In the study titled "Lack of galectin-3 alters the balance of innate immune cytokines and confers resistance to Rhodococcus equi infection," Brazilian researchers found that mice lacking galectin-3 (gal3-/-) were more resistant to experimental infection with R. equi than were gal3+/+ mice during the early stages of infection.1 The LD50 for the gal3-deficient mice was seven times higher than that for the wild-type gal3+/+ mice. Furthermore, higher IL-1β levels were detected in the spleens of gal3-/- mice, suggesting that galectin-3 may decrease IL-1β synthesis by macrophages to ultimately confer resistance to R. equi.

    The effect of IL-1β-related genes on the development of R. equi infection was evaluated by Horin et al.2 Previously, this group found significant association between horse chromosome 15 (ECA15) microsatellite markers HMSO1 and HTG06 and infection with R. equi.3 The group stated, "Interleukin-1b subunit and interleukin-1 receptor-antagonist encoding genes (IL-1β and IL-1RN) could be considered as candidate genes underlying the associations reported." Therefore, in the group's latest study, it evaluated single nucleotide polymorphisms (i.e., variations in DNA sequences that alter a single nucleotide in the genome that differs between members of the same species or between paired chromosomes in an individual) in three interleukin-1b functionally related genes: IL-1β, IL-1RN, and Casp1 (interleukin-1b converting enzyme/caspase1 encoding gene).

    Using polymerase chain reaction testing, these researchers previously classified 50 foals as negative or positive for R. equi based on more than 5000 colonies/mL from transtracheal aspirates. In the most recent study, they classified these foals as Casp1 174G carriers or Casp1 174G negative, and "a significant association (P < .03) with the presence of R. equi in the tracheal lavage was found." However, there were no statistically significant differences between IL-1β and IL-1RN polymorphisms in R. equi shedding status.

    Further research in horses is warranted, considering the novel findings reported in these studies and the importance of R. equi in the equine industry.

    Dr. Oke discloses that she has received financial benefits from Nutramax Laboratories, Inc.

    1. Ferraz LC, Bernardes ES, Oliveira AF, et al. Lack of galectin-3 alters the balance of innate immune cytokines and confers resistance to Rhodococcus equi infection. Eur J Immunol 2008;38:1-14.

    2. Horin P, Osickova J, Necesankova M, et al. Single nucleotide polymorphisms of interleukin-1beta-related genes and their associations with infection in the horse. Dev Biol (Basel) 2008;132:347-351.

    3. Horin P, Smola J, Matiasovic J, et al. Polymorphisms in equine immune response genes and their associations with infections. Mamm Genome 2004;15:843-850.

    References »

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