June 2023
Volume 64, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2023
Conjunctival caspase-6 and plasmacytes increased by topical muramyl dipeptide
Author Affiliations & Notes
  • Marlyn P Langford
    Ophthalmology, LSU Health Shreveport, Shreveport, Louisiana, United States
  • Thomas B Redens
    Ophthalmology, LSU Health Shreveport, Shreveport, Louisiana, United States
  • William A Byrd
    Ophthalmology, LSU Health Shreveport, Shreveport, Louisiana, United States
  • Footnotes
    Commercial Relationships   Marlyn Langford None; Thomas Redens None; William Byrd None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science June 2023, Vol.64, 3915. doi:
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      Marlyn P Langford, Thomas B Redens, William A Byrd; Conjunctival caspase-6 and plasmacytes increased by topical muramyl dipeptide. Invest. Ophthalmol. Vis. Sci. 2023;64(8):3915.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Tear immunoglobulin (Ig) levels are elevated by topical application of the bacterial cell wall peptidoglycan/adjuvant, muramyl dipeptide (MDP). Caspase-6 activity has been reported to play a role in peripheral B cell differentiation. We present acute increases in conjunctival caspase-6 activity and IgG plasmacyte accumulation in ipsilateral rabbit eyes post topical MDP application consistent with the possibility of MDP-induced local B-cell differentiation.

Methods : Cytopathology was assessed by hematoxylin and eosin staining. Tear caspse-6 activity was detected by substrate-specific colorimetric assay. Bilateral tear protein was determined by standard assay and IgG concentrations were detected by enzyme-linked immunosorbent assay (ELISA). Dual-labeling immunofluorescent antibody method detected caspase-6-positive leukocytes and IgG plasmacytes.

Results : The onset of symptoms of ipsilateral conjunctivitis at 3-5h post topical MDP application was concomitant with significant increases in ipsilateral tear protein, caspase-6 activity, and IgG. Protein levels were significantly higher in the ipsilateral than contralateral tears 3-6 h post MDP. Caspase-6 levels were higher in ipsilateral tear than contralateral tear levels at 4 (37.3±7.3 versus 19.7±4.5 U/ml; p=0.04) and 5 h (31±4.1 U/ml versus 17.3±8.6; p=0.05) and conjunctival tissue (157±9 versus 116±20 U/ml; p=0.016) at 5 h post MDP. Ipsilateral tear IgG levels were significantly higher and IgG-positive plasmacytes were more numerous in affected ipsilateral than unaffected contralateral conjunctiva at 5h.

Conclusions : The results support MDP-induced permeability, caspase-6 activation, and accumulation of IgG plasmacytes in conjunctival tissue. While the cytology, tear protein, and IgG levels suggests ipsilateral conjunctival barrier breakdown, the increase in caspase-6 and IgG plasmacytes suggests local conjunctival IgG production may result via MDP activated caspase-6 mediated B-cell differentiation.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

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