Objective—To evaluate immunomodulatory properties of all-trans retinoic acid and a fully oxidized β-carotene dietary product in calves with Mannheimia haemolytica–induced pneumonia.
Animals—Twenty-five 6- to 10-week-old male Holstein calves for experimental inoculations and three 8- to 30-week-old Angus heifers for blood donations.
Procedures—In vitro, neutrophils and monocyte-derived macrophages isolated from blood of healthy Angus heifers were treated with all-trans retinoic acid (1μM) or fully oxidized β-carotene (8.3 μg/mL) for various times and assessed for markers of cellular death, antimicrobial function, and production of proinflammatory leukotriene B4. Following 28 days of dietary supplementation with fully oxidized β-carotene, Holstein calves were experimentally inoculated with M haemolytica. Bronchoalveolar lavage fluid was collected at 3 and 24 hours after challenge inoculation and analyzed for markers of apoptosis.
Results—In vitro, all-trans retinoic acid and fully oxidized β-carotene induced cell-selective, caspase-3–dependent apoptosis in neutrophils, which subsequently enhanced efferocytosis in macrophages. Conversely, neither treatment altered phorbol 12-myristate 13-acetate–induced oxidative burst, phagocytosis of nonopsonized zymosan (complement or antibody independent), or M haemolytica–induced leukotriene B4 production in bovine neutrophils. In vivo, fully oxidized β-carotene enhanced leukocyte apoptosis in bronchoalveolar lavage fluid as well as subsequent efferocytosis by macrophages without altering numbers of circulating leukocytes.
Conclusions and Clinical Relevance—Neutrophil apoptosis and subsequent efferocytosis by macrophages are key mechanisms in the resolution of inflammation. Findings for the present study indicated that all-trans retinoic acid and fully oxidized β-carotene could be novel nutraceutical strategies that may confer anti-inflammatory benefits for cattle with respiratory tract disease.
Procedure—Piglets were assigned to 1 of 4
groups as follows: 1) uninfected sham-treated control
piglets; 2) infected untreated piglets that were
intratracheally inoculated with 107 CFUs of A pleuropneumoniae;
3) infected treated piglets that were
intratracheally inoculated with A pleuropneumoniae
and received tilmicosin in feed (400 ppm [µg/g]) for
7 days prior to inoculation; or 4) infected treated
piglets that were intratracheally inoculated with A
pleuropneumoniae and received chlortetracycline
(CTC) in feed (1,100 ppm [µg/g]) for 7 days prior to
inoculation. Bronchoalveolar lavage (BAL) fluid and
lung tissue specimens of piglets for each group
were evaluated at 3 or 24 hours after inoculation.
For each time point, 4 to 6 piglets/group were studied.
Results—Feeding of CTC and tilmicosin decreased
bacterial load in lungs of infected piglets. Tilmicosin
delivered in feed, but not CTC, enhanced apoptosis
in porcine BAL fluid leukocytes. This was associated
with a decrease in LTB4 concentrations in BAL fluid
of tilmicosin-treated piglets, compared with untreated
and CTC-treated piglets, and also with a significant
decrease in the number of pulmonary lesions.
Tilmicosin inhibited infection-induced increases in
rectal temperatures, as measured in untreated and
CTC-treated piglets. Pulmonary neutrophil infiltration
and prostaglandin E2 concentrations in the BAL fluid
were not significantly different among groups at any
Conclusions and Clinical Relevance—Oral administration
of tilmicosin to infected piglets induces apoptosis
in BAL fluid leukocytes and decreases BAL fluid
LTB4 concentrations and inflammatory lung lesions.
(Am J Vet Res 2005;66:100–107)
OBJECTIVE To investigate the anti-inflammatory and immunomodulatory properties of tulathromycin in vitro and in experimental models of Actinobacillus pleuropneumoniae–induced pleuropneumonia and zymosan-induced pulmonary inflammation in pigs.
ANIMALS Blood samples from six 8- to 30-week-old healthy male pigs for the in vitro experiment and sixty-five 3-week-old specific pathogen–free pigs.
PROCEDURES Neutrophils and monocyte-derived macrophages were isolated from blood samples. Isolated cells were exposed to tulathromycin (0.02 to 2.0 mg/mL) for various durations and assessed for markers of apoptosis and efferocytosis. For in vivo experiments, pigs were inoculated intratracheally with A pleuropneumoniae, zymosan, or PBS solution (control group) with or without tulathromycin pretreatment (2.5 mg/kg, IM). Bronchoalveolar lavage fluid was collected 3 and 24 hours after inoculation and analyzed for proinflammatory mediators, leukocyte apoptosis, and efferocytosis.
RESULTS In vitro, tulathromycin induced time- and concentration-dependent apoptosis in neutrophils, which enhanced their subsequent clearance by macrophages. In the lungs of both A pleuropneumoniae– and zymosan-challenged pigs, tulathromycin promoted leukocyte apoptosis and efferocytosis and inhibited proinflammatory leukotriene B4 production, with a concurrent reduction in leukocyte necrosis relative to that of control pigs. Tulathromycin also attenuated the degree of lung damage and lesion progression in A pleuropneumoniae–inoculated pigs.
CONCLUSIONS AND CLINICAL RELEVANCE Tulathromycin had immunomodulatory effects in leukocytes in vitro and anti-inflammatory effects in pigs in experimental models of A pleuropneumoniae infection and nonmicrobial-induced pulmonary inflammation. These data suggested that in addition to its antimicrobial properties, tulathromycin may dampen severe proinflammatory responses and drive resolution of inflammation in pigs with microbial pulmonary infections.