Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2005
Publication Date: 9/15/2005
Citation: Bannerman, D.D., Chockalingam, A., Paape, M.J., Hope, J.C. 2005. The bovine innate immune response during experimentally-induced pseudomonas aeruginosa mastitis. Veterinary Immunology and Immunopathology. 107(3-4):201-215.
Interpretive Summary: Pseudomonas aeruginosa is a Gram-negative bacterial pathogen that induces bovine mastitis. Among the Gram-negative bacteria that cause this disease, Pseudomonas aeruginosa remains the most resistant to conventional antibiotics. Since the ability of bacteria to establish infection is due, in part, to the ability of the host to mount an immune/inflammatory response to the bacteria, this study characterizes the innate immune response of cows to intramammary infection with Pseudomonas aeruginosa. By increasing our understanding of mammary gland host immune defense mechanisms, new therapeutics may be developed that can enhance/alter the immune response, thus, providing new treatments for curing an infection caused by a bacterium currently resistant to conventional antibiotics.
Technical Abstract: Almost half of all clinical cases of mastitis are caused by Gram-negative bacteria. Of the Gram-negative bacteria that cause mastitis, Pseudomonas aeruginosa remains one of the most prevalent. The ability to recognize potentially harmful pathogens whether previously encountered or not, as well as the induction of an initial pro-inflammatory response to these pathogens, are critical components of host innate immunity. Although the innate immune response to another Gram-negative mastitis-causing pathogen, Escherichia coli, has been well-characterized, little is known about the response to other Gram-negative bacteria, including Pseudomonas aeruginosa. The objective of the current study was to characterize the systemic and localized bovine innate immune response to intramammary infection with Pseudomonas aeruginosa. The contralateral quarters of ten mid-lactating Holstein cows were challenged with either saline or Pseudomonas aeruginosa. Following the establishment of infection, milk samples were collected and assayed for changes in cytokine and growth factor concentrations, complement activation, and changes in the levels of soluble CD14 (sCD14) and lipopolysaccharide (LPS)-binding protein (LBP), two accessory molecules involved in host recognition of Gram-negative bacteria. Initial increases in milk somatic cell counts were evident within 12 h of experimental challenge and remained elevated for >6 weeks. Increased permeability of the mammary gland vasculature, as evidenced by elevated milk levels of BSA, was initially observed 20 h post-infection and persisted for 2 weeks. Within 32 h of challenge, increased levels of IL-8, TNF-alpha, IL-10, and IL-12 were detected, however, the elevated levels of these cytokines were not sustained for longer than a 24 h period. In contrast, elevations in IL-1beta, IFN-gamma, TGF-alpha, TGF- beta1, TGF-' beta2, sCD14, LBP, and activated complement factor 5 (C5a) were sustained for periods of >48 h. Systemic changes were characterized by elevated body temperature, induction of the acute phase protein synthesis of serum amyloid A and LBP, and a transient decrease in circulating neutrophils and lymphocytes. Together, these data demonstrate the capability of the mammary gland to mount a robust innate immune response to Pseudomonas aeruginosa that is characterized by the induction of pro-inflammatory cytokines, complement activation, and increased levels of accessory molecules involved in Gram-negative bacterial recognition.