Class A scavenger receptor expression and function in eight novel tadpole cell lines from the green frog (Lithobates clamitans) and the wood frog (Lithobates sylvatica).

A total of eight tadpole cell lines were established from green frogs (Lithobates clamitans) and wood frogs (Lithobates sylvatica). The five green frog cell lines were named GreenTad-HF1, GreenTad-HF2, GreenTad-HF3, GreenTad-HE4, and GreenTad-gill. The three wood frog cell lines were named WoodTad-HE1, WoodTad-Bone, and WoodTad-rpe. DNA barcoding confirmed the cell lines to be from the correct species and the growth characteristics (optimal temperature and FBS requirement) were elucidated. In order to begin studying the innate immune capacity for each cell line, class A scavenger receptor expression and function were next explored. All cell lines expressed genes for at least 3 of the 5 class A scavenger receptor (SR-A) family members, but the gene expression patterns varied between cell lines. MARCO was only expressed in GreenTad-HE4 and WoodTad-Bone, while only GreenTad-HF3 did not express SCARA5 and only WoodTad-rpe did not express SR-AI. Acetylated low density lipoprotein (AcLDL) is a well-defined ligand for SR-As and WoodTad-rpe was the only cell line to which it was unable to bind. In the other seven tadpole cell lines, the SR-A competitive ligands (dextran sulfate, fucoidan, polyinosinic acid) blocked AcLDL binding whereas the SR-A non-competitive ligand counterparts (chondroitin sulfate, fetuin, polycytidylic acid, respectively) did not. Overall, these new eight cell lines can become important tools in the study of innate immunity in general and SR-A functions in particular in green frogs and wood frogs.