Submitted to: Veterinaria Mexico
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/1997
Publication Date: N/A
Interpretive Summary: Respiratory tract diseases are a leading cause of loss from disease in the cattle, sheep and goat industries. Annual loss in the United States is estimated to exceed one billion dollars. Losses are from mortality, reduced feed efficiency, and slaughter condemnations, as well as prevention and treatment measures. Currently, not all the factors leading to the development of pneumonia are known by scientists and veterinarians. As part of our ongoing studies to understand the disease process, we found that antibodies to some bacterial products did not neutralize the inflammatory response in the lungs of rabbits but actually exacerbated the inflammatory response. On the basis of our findings, it appears that this would be an important factor in the disease process. Our findings are an important first step in the development of a new vaccine that can be used to better control shipping fever of cattle. Corollary benefits include an increase in the profitability and international competitiveness of the U. S. cattle industry, a stronger rural economy, and a continued supply of inexpensive, wholesome beef, and beef products for the American consumer.
Technical Abstract: A local Shwartzman reaction (SR) was induced in the lungs of rabbits with Pasteurella haemolytica (type A1) lipopolysaccharide (LPS). The lesions resembled, in part, those seen in pneumonic pasteurellosis of cattle. In this study, the effects of antibodies on the intensity of the SR was examined in rabbits. One group of rabbits was passively immunized with 4 ml of antiserum obtained from rabbits immunized with a whole-cell bacterin (P. haemolytica strain 82-25, IHA titer to strain 82-25 LPS was 1:2560). The other group of rabbits was not immunized. At 24 hours post immunization (PI) rabbits in both groups were subdivided. The SR was induced in both groups by injecting a 50 ug preparatory dose of LPS intratracheally (IT), followed in 24 hours (48 hours PI) by a 100 ug provocative dose of LPS intravenously (IV). Control groups of rabbits received LPS IT/pyrogen free saline (PFS) IV or PFS IT/LPS IV. At 12 hours safter IV inoculation (60 hours PI), all rabbits were euthanized and exsanguinated. The histopathological changes seen in the SR were similar to those seen in rabbits that received LPS IT/PFS IV, indicating the lesion were primarily in response to IT LPS inoculation. Passive immunization of rabbits resulted in a variable inflammatory response to the LPS; some rabbits had mild lung lesions, but others had more severe lesions than non- immunized rabbits. Passive immunized rabbits also had higher total and differential bronchoalveolar lavage cell counts. In summary, a) IT LPS inoculation was more inflammatory than IV LPS and IT LPS/IV LPS (SR) in either passively or non-immunized rabbits and b) passive immunization exacerbates the lung inflammatory response.