Defects in host immune function in tree frogs with chronic chytridiomycosis.

Area of Science:

• Amphibian immunology
• Pathogen-host interactions
• Wildlife disease ecology

Background:

• The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), is a major driver of global amphibian declines.
• Previous research observed in vitro immunosuppressive effects of Bd on lymphocytes.
• The in vivo impact of Bd on host immune competence remained largely unknown.

Purpose of the Study:

• To investigate the in vivo effects of experimental Batrachochytrium dendrobatidis (Bd) infection on the immune competence of two tree frog species.
• To identify potential mechanisms underlying host susceptibility or resistance to Bd infection.

Main Methods:

• Experimental infection of Litoria caerulea and Litoria infrafrenata with Bd.
• Assessment of immune competence using hematologic biomarkers, protein electrophoresis, and functional immune tests.
• Analysis of immunoglobulin and lymphocyte responses to sheep red blood cell antigen stimulation.

Main Results:

• Bd infection in Litoria caerulea led to reduced immunoglobulin and splenic lymphocyte responses, decreased white blood cell counts, and lower serum protein concentrations.
• These findings suggest impaired systemic immune function in Bd-infected L. caerulea.
• Litoria infrafrenata cleared Bd infection, but exhibited lower white blood cell and serum globulin levels post-infection, indicating potential resource reallocation or systemic costs.

Conclusions:

• This study provides the first in vivo evidence that Batrachochytrium dendrobatidis infection causes multiple defects in systemic host immune function, contributing to disease susceptibility.
• While L. caerulea showed signs of immunosuppression, L. infrafrenata's resistance may involve localized or innate immunity, with potential costs associated with infection clearance.