Immune Cells Remain in the Cornea Even After Allergic Conjunctivitis Eases

Underlying inflammation in corneal tissue persists even after allergic conjunctivitis becomes inactive, according to research published in Eye — although it does not persist in the conjunctiva. The study shows dendritic cells in both symptomatic and asymptomatic phases of this disorder maintain a similar density.

The study included 20 individuals (mean age, 43.3±14.3 years; 55% women) who had experienced allergic conjunctivitis and maintained 4 weeks or more of symptom-free status. All participants had a positive skin test for at least 1 allergen: pet dander, plant or tree pollen, dust mites, or mold. Investigators assessed signs, symptoms, and data from in vivo confocal microscopy (IVCM) to compare symptomatic vs inactive phases. Also, records for nonallergic individuals were compared with allergic, asymptomatic patients.

When comparing regions of the cornea during active and nonactive phases, IVCM revealed no significant differences in dendritiform immune cell density (P ≥.22). However, in looking at asymptomatic allergic patients vs nonallergic controls, density for those with allergies was higher at corneal center (P =.01), inferior whorl (P =.03), and corneal periphery (P =.004) — except not at the limbus, where dendritic cells decreased to almost normal levels for most nonactive patients. Researchers suggest since limbal lymphatic vessels are nearby, cells may easily move toward lymph node drainage. 

In the bulbar conjunctiva, dendritic density decreased from active to asymptomatic phase (P =.01), though did not differ when comparing nonactive allergic with nonallergic individuals (P =.70). Investigators added that quicker stabilization from active allergic to noninflamed status could result from conjunctival lymphatic vessels which may manage back-and-forth flow of dendritic cells.

Regarding morphology, dendritic cell body size in the cornea contracted in allergic nonactive patients (P ≤.01), although it did not change in the conjunctiva (P =.10). There were also significantly fewer long dendrite arms at the corneal center and limbus (P ≤.02). Comparison of asymptomatic vs healthy eyes showed nonactive allergic active eyes had smaller dendritic cell body size in the corneal limbus (P =.003), along with fewer dendrites or long dendrites (P ≤.01).

Previous immunohistochemistry studies indicate a correlation between dendritic cell shape and activation marker expression; for example, shorter dendrites are not able to capture as much antigen and are displayed in nonallergic eyes. 

“The findings from this study suggest that DC density and morphology may be more sensitive markers of inflammation than allergic symptoms and other clinical signs and should perhaps be considered in the therapeutic decision-making for allergic eye diseases,” investigators explain.

A limitation of this investigation is that IVCM cannot verify a cell’s phenotype or identify specific markers on cell surfaces — immunohistochemistry was not performed in this study. However, this is the first analysis of dendritic cell density and morphology to evaluate immune-related processes in active and inactive stages of allergic conjunctivitis.