Assessment of the immune capacity of mammary epithelial cells: comparison with mammary tissue after challenge with Escherichia coli

Abstract

We examined the repertoire and extent of inflammation dependent gene regulation in a bovine mammary epithelial cell (MEC) model, to better understand the contribution of the MEC in the immune defence of the udder. We challenged primary cultures of MEC from cows with heat inactivated Escherichia coli pathogens and used Affymetrix DNA-microarrays to profile challenge related alterations in their transcriptome. Compared to acute mastitis, the most prominently activated genes comprise those encoding chemokines, interleukins, beta-defensins, serum amyloid A and haptoglobin. Hence, the MEC exert sentinel as well as effector functions of innate immune defence. E. coli stimulated a larger fraction of genes (30%) in the MEC belonging to the functional category Inflammatory Response than we recorded with the same microarrays during acute mastitis in the udder (17%). This observation underscores the exquisite immune capacity of MEC. To more closely examine the adequacy of immunological regulation in MEC, we compared the inflammation dependent regulation of factors contributing to the complement system between the udder versus the MEC. In the MEC we observed only up regulation of several complement factor-encoding genes. Mastitis, in contrast, in the udder strongly down regulates such genes encoding factors contributing to both, the classical pathway of complement activation and the Membrane Attack Complex, while the expression of factors contributing to the alternative pathway may be enhanced. This functionally polarized regulation of the complex complement pathway is not reflected in the MEC models.

Figure 1.

Validation of cell types in pbMEC cultures. pbMEC cultures were stained with antibodies against cytokeratin 18 (anti-Cy18) or smooth muscle actin (anti-Actin). The udder section (right) was stained with anti-actin to show the in situ arrangement of myoepithelial cells. Nuclei were stained in tissue cultures with DAPI and with ethidium bromide in udder sections.

Figure 2.

Expressional regulation of complement genes, E. coli infected udders or E. coli stimulated pbMEC. Genes with a ≥ 1.5-fold expression change are listed. Genes with a ≥ 2-fold expression change are in bold letters. Arrows indicate up- or down-regulation of mRNA abundance. Udders (infected) or pbMEC (stimulated) were both challenged for 24 h.