Insights on Immune Function in Free-Ranging Green Sea Turtles (Chelonia mydas) with and without Fibropapillomatosis

Chelonid alphaherpesviruses 5 and 6 (ChHV5 and ChHV6) are viruses that affect wild
sea turtle populations. ChHV5 is associated with the neoplastic disease fibropapillomatosis (FP),
which affects green turtles (Chelonia mydas) in panzootic proportions. ChHV6 infection is associated
with lung-eye-trachea disease (LETD), which has only been observed in maricultured sea turtles,
although antibodies to ChHV6 have been detected in free-ranging turtles. To better understand
herpesvirus prevalence and host immunity in various green turtle foraging aggregations in Florida,
USA, our objectives were to compare measures of innate and adaptive immune function in relation
to (1) FP tumor presence and severity, and (2) ChHV5 and ChHV6 infection status. Free-ranging,
juvenile green turtles (N = 45) were captured and examined for external FP tumors in Florida’s Big
Bend, Indian River Lagoon, and LakeWorth Lagoon. Blood samples were collected upon capture
and analyzed for ChHV5 and ChHV6 DNA, antibodies to ChHV5 and ChHV6, in vitro lymphocyte
proliferation using a T-cell mitogen (concanavalin A), and natural killer cell activity. Despite an
overall high FP prevalence (56%), ChHV5 DNA was only observed in one individual, whereas 20% of
turtles tested positive for antibodies to ChHV5. ChHV6 DNA was not observed in any animals and
only one turtle tested positive for ChHV6 antibodies. T-cell proliferation was not significantly related
to FP presence, tumor burden, or ChHV5 seroprevalence; however, lymphocyte proliferation in
response to concanavalin A was decreased in turtles with severe FP (N = 3). Lastly, green turtles with
FP (N = 9) had significantly lower natural killer cell activity compared to FP-free turtles (N = 5). These
results increase our understanding of immune system effects related to FP and provide evidence that
immunosuppression occurs after the onset of FP disease.