Spleen and head kidney differential gene expression patterns in trout with clinical signs of lactococcosis caused by Lactococcus garvieae

Lactococcus garvieae is the etiological agent of lactococcosis, a hemorrhagic septicaemia that affects marine and freshwater fish, with special incidence and economic relevance in farmed rainbow trout and with potential zoonotic risks. To characterize the trout immune response at the transcriptomic level on those individuals with clinical signs of lactococcosis, we have performed a microarray analysis using a previously validated immune-focused gene design. The analysis of the transcriptome of spleen and kidney reveals a different pattern of transcription between both immune organs. A correlation between the histopathological examination and the expression patterns of gene sets characterizing immune cell populations was observed for the first time in the spleen. Up-regulation of gene sets key to NK cells, cytotoxic T cells, Th1 and Th2 lymphocytes and macrophages correlated with the inflammatory process and the existence of granulomes containing a high number of macrophages with internalized L. garvieae. On the other hand, cell wall peptidoglican seems to be an important antigen able to induce a complex network of pathways, cytokine production and responses in the host. 3 pools for control spleen samples (9 arrays), 3 pools for L. garvieae-infected spleen samples (9 arrays), 2 pools for control kidney samples (5 arrays), and 3 pools for L. garvieae-infected kidney samples (9 arrays).