Inflammation and degeneration of the olfactory epithelium in an immuno-deficient zebrafish

Vertebrates are protected from pathogens by an adaptive and an innate immune system. In mammals, loss of the adaptive immune system severely compromises viability. Zebrafish, in contrast, can survive for relatively long without adaptive immunity, as demonstrated by the immuno-deficient Rag1 mutant. Here, we examine whether the innate immune system is activated in the mutant, and ask whether this has any effect on the nervous system, given the finding that inflammation is linked to neurodegeneration in higher vertebrates. Using microarray analysis of the olfactory epithelium, we show that innate immune responses are upregulated. Neuronal genes are down-regulated, and immunofluorescence for the neural marker HuC shows a progressive loss of olfactory sensory neurons in mutants. Propodium iodide uptake indicates a corresponding increase in cell death. Rag1 mutant fish progressively lose their sensitivity to an olfactory cue, the alarm pheromone Schreckstoff, indicating that neuro-degeneration has a behavioral significance. Taken together, these data establish that immuno-deficiency in the zebrafish is accompanied by neuro-inflammation and loss of neurons. The microarray data document transcriptional changes associated with activation of innate immunity in the context of immunodeficiency and also identify novel genes that are potentially related to function of the olfactory system. Keywords: analysis of mutant A total of 6 RNA samples were used for hybridization. 3 were from the olfactory rosettes of wild type adult zebrafish and 3 were from Rag1 mutants.