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.