Cloning of Syrian Hamster ( Mesocricetus auratus ) Cytokine cDNAs and Analysis of Cytokine mRNA Expression in Experimental Visceral Leishmaniasis

The Syrian golden hamster ( Mesocricetus auratus ) is uniquely susceptible to a variety of intracellular pathogens and is an excellent model for a number of human infectious diseases. The molecular basis for this high level of susceptibility is unknown, and immunological studies related to this model have been limited by the lack of available reagents. In this report we describe the cloning and sequence analysis of portions of the Syrian hamster interleukin 2 (IL-2), IL-4, gamma interferon (IFN-γ), tumor necrosis factor alpha, IL-10, IL-12p40, and transforming growth factor β cDNAs. In addition, we examined the cytokine response to infection with the intracellular protozoan Leishmania donovani in this animal model. Sequence analysis of the hamster cytokines revealed 69 to 93% homology with the corresponding mouse, rat, and human nucleotide sequences and 48 to 100% homology with the deduced amino acid sequences. The hamster IFN-γ, compared with the mouse and rat homologs, had an additional 17 amino acids at the C terminus that could decrease the biological activity of this molecule and thus contribute to the extreme susceptibility of this animal to intracellular pathogens. The splenic expression of these genes in response to infection with L. donovani , the cause of visceral leishmaniasis (VL), was determined by Northern blotting. VL in the hamster is a progressive, lethal disease which very closely mimics active human disease. In this model there was pronounced expression of the Th1 cytokine mRNAs, with transcripts being detected as early as 1 week postinfection. Basal expression of IL-4 in uninfected hamsters was prominent but did not increase in response to infection with L. donovani . IL-12 transcript expression was detected at low levels in infected animals and paralleled the expression of IFN-γ. Expression of IL-10, a potent macrophage deactivator, increased throughout the course of infection and could contribute to the progressive nature of this infection. These initial studies are the first to examine the molecular immunopathogenesis of a hamster model of VL infection and indicate that progressive disease in this model of VL is not associated with early polarization of the splenic cellular immune response toward a Th2 phenotype and away from a Th1 phenotype.