Purinergic signaling modulates the cerebral inflammatory response in experimentally infected fish with Streptococcus agalactiae: an attempt to improve the immune response.

Appropriate control of the immune response is a critical determinant of fish health, and the purinergic cascade has an important role in the immune and inflammatory responses. This cascade regulates the levels of adenosine triphosphate (ATP), adenosine diphosphate, adenosine monophosphate and adenosine (Ado), molecules involved in physiological or pathological events as inflammatory and anti-inflammatory mediators. Thus, the aim of this study was to evaluate whether purinergic signaling, through the activities of nucleoside triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase, and adenosine deaminase (ADA), is capable of modulating the cerebral immune and inflammatory responses in silver catfish that is experimentally infected with Streptococcus agalactiae. Cerebral NTPDase (with ATP as substrate) and 5'-nucleotidase activities increased, while ADA activity decreased in silver catfish that is experimentally infected with S. agalactiae, compared to the control group. Moreover, the cerebral levels of ATP and Ado increased in infected animals compared to the uninfected control group. Brain histopathology in infected animals revealed inflammatory demyelination (the presence of occasional bubbly collections), increased cellular density in the area near to pia-mater and intercellular edema. Based on this evidence, the modulation of the purinergic cascade by the enzymes NTPDase, 5'-nucleotidase, and ADA exerts an anti-inflammatory profile due to the regulation of ATP and Ado levels. This suggests involvement of purinergic enzymes on streptococcosis pathogenesis, through regulating cerebral ATP and Ado levels, molecules known to participate in physiological or pathological events as inflammatory and anti-inflammatory mediators, respectively. In summary, the modulation of the cerebral purinergic cascade exerts an anti-inflammatory profile in an attempt to reduce inflammatory damage.