Perturbations in cytokine gene expression after inoculation of C57BL/6 mice with Pasteurella pneumotropica.

Pasteurella pneumotropica can cause inflammation and abscess formation in a variety of tissues. Most commonly, P. pneumotropica produces clinical disease in immunodeficient mice or those concurrently infected with other pathogens. Because clinical disease is infrequent in immunocompetent mice harboring P. pneumotropica, some scientists consider it an opportunistic pathogen with little clinical relevance to biomedical research. However, other infectious agents, including mouse parvoviruses, mouse rotavirus, and Helicobacter spp. alter physiologic or biologic responses without causing clinical signs of illness. We investigated the potential for P. pneumotropica to modulate the transcription of cytokine genes in immunocompetent mice. In C57BL/6 mice inoculated oronasally with a minimal colonizing dose of P. pneumotropica, modest but statistically significant elevations of IL1beta, TNFalpha, CCL3, CXCL1, and CXCL2 mRNA were detected in mandibular and superficial cervical lymph nodes at 7 d after inoculation, and upregulation of IL1beta mRNA was detected 28 d after inoculation. These perturbations were not present in C57/BL6 mice inoculated with heat killed-P. pneumotropica or the related bacterium Actinobacillus muris. Nasal mucosal cytokine transcription did not vary significantly in C57BL/6 mice given a high dose of P. pneumotropica. These data indicate that slight and transient experimental perturbations are possible in immunocompetent mice colonized with P. pneumotropica. Knowing the full health status of experimental mice is paramount to avoid unwanted experimental variables, especially when using exquisitely sensitive testing methodologies such as those for quantification of gene expression.