Functional immune response in Pecten maximus: Combined effects of a pathogen-associated molecular pattern and PAH exposure

Pathogen-associated molecular patterns (PAMPs) enable recognition of structures present in microorganisms such as lipopolysaccharides (LPS). LPS are an essential constituent of the outer membrane of Gram-negative bacteria, stimulating the innate immune system of invertebrates. Here, LPS from Escherichia coli (055:B5) were used to investigate the functional immune response of Pecten maximus after stimulation with a PAMP and to determine the combined effect of a phenanthrene exposure and LPS challenge. Organisms were exposed to 200 μg l−1 phenanthrene and after 7 d were injected with either physiological saline (injection controls) or LPS solution, and returned to their respective exposure tanks. Haemolymph was sampled from the scallops 48 h post-injection and immune function was assessed using a combination of cellular biological responses. The LPS challenge significantly altered the immune response in P. maximus with increased cell counts and phagocytic activity. An immunosuppressive effect of phenanthrene was also observed in this study; however, exposure to phenanthrene did not significantly impair the organism's ability to respond to a PAMP challenge. The overall level of phagocytosis and cytotoxic capability following the LPS challenge was lower in phenanthrene exposed scallops and may have consequences for disease resistance in this commercially-exploited species.