Characterisation of the TNF superfamily members CD40L and BAFF in the small-spotted catshark (Scyliorhinus canicula)

• CD40L and BAFF were cloned from the small-spotted catshark Scyliorhinus canicula.
• Both catshark CD40L and BAFF are highly expressed in shark immune tissues.
• CD40L and BAFF expression levels are altered following in vitro stimulation of catshark PBLs.
• CD40L levels correlate with those of TCRα in various catshark tissues.
• Cartilaginous fish CD40L and BAFF carry insertions that may alter their receptor binding site.

The tumour necrosis factor superfamily (TNFSF) members CD40L and BAFF play critical roles in mammalian B cell survival, proliferation and maturation, however little is known about these key cytokines in the oldest jawed vertebrates, the cartilaginous fishes. Here we report the cloning of CD40L and BAFF orthologues (designated ScCD40L and ScBAFF) in the small-spotted catshark (Scyliorhinus canicula). As predicted both proteins are type II membrane-bound proteins with a TNF homology domain in their extracellular region and both are highly expressed in shark immune tissues. ScCD40L transcript levels correlate with those of TCRα and transcription of both genes is modulated in peripheral blood leukocytes following in vitro stimulation. Although a putative CD40L orthologue was identified in the elephant shark genome the work herein is the first molecular characterisation and transcriptional analysis of CD40L in a cartilaginous fish. ScBAFF was also cloned and its transcription characterised in an attempt to resolve the discrepancies observed between spiny dogfish BAFF and bamboo shark BAFF in previously published studies.