Abstract
Purpose :
The gut microbiota has been associated with immune-mediated uveitis in several studies. Mounting evidence indicates that translocation of microbes or microbial products from the gut may promote inflammation in the eye. We hypothesize that each tissue in the eye has a different composition of pattern recognition receptors (PRR) which might explain the variety of clinical features of immune-mediated uveitis. For this reason we investigated the PRR composition on porcine iris, retina and choroid. In addition, we sought to demonstrate the expression of cytokines in porcine iris, retina and choroid tissues stimulated by microbe-associated molecular patterns (MAMPs).
Methods :
Freshly enucleated porcine eyes were dissected and tissues including iris, retina and choroid were biopsied. Tissues were subsequently stimulated overnight with microbial or fungal MAMPs (LPS, TL8-506, NG-MDP, FLA-ST or Curdlan). Cytokine (IL-6, IL-8, IL-1β, IL-12 and IL-23) mRNA expression was subsequently determined by qRT-PCR The expression of PRRs Dectin-1, DC-SIGN, TLR4, TLR8 and NOD2; and Dectin-1 signaling component Syk was also determined in these tissues by qRT-PCR. Relative expression of mRNA was normalized to housekeeping gene HPRT and compared to unstimulated controls.
Results :
We found that expression of PRRs and Syk was present in all tissues, although substantially lower in retina compared to iris and choroid. MAMP-induced cytokine expression was also lowest in retina. The most strongly induced cytokines following MAMP stimulation were IL-1β, IL-6, and strikingly IL-23 with a minimal IL-12 response. Interestingly both microbial and particularly fungal (Curdlan) MAMPs elicited potent cytokine responses in both iris and choroid.
Conclusions :
Retina, choroid and iris each express PRRs although with varying expression by tissue type. This was also paralleled by differential responses to MAMP-stimulation. None of these tissues was completely refractory to PRR stimulation, although diminished responses were observed in retina. Interestingly, a wide-range of microbial and fungal MAMPs were found to elicit inflammatory response in ocular tissues. Of these, Curdlan-induced IL-23 expression may be particularly relevant to the Th17 signature response known to accompany uveitis.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.