Comparison of pulmonary defense mechanisms in Rocky Mountain bighorn (Ovis canadensis canadensis) and domestic sheep

Comparative nitric oxide production by LPS-stimulated monocyte-derived macrophages from Ovis canadensis and Ovis aries

Bighorn sheep are more susceptible to respiratory infection by Mannheimia haemolytica than are domestic sheep. In response to bacterial challenge, macrophages produce a number of molecules that play key roles in the inflammatory response, including highly reactive nitrogen intermediates such as nitric oxide (NO). Supernatants from monocyte-derived macrophages cultured with M. haemolytica LPS were assayed for nitric oxide activity via measurement of the NO metabolite, nitrite. In response to LPS stimulation, bighorn sheep macrophages secreted significantly higher levels of NO compared to levels for non-stimulated macrophages. In contrast, levels of NO produced by domestic sheep macrophages in response to M. haemolytica LPS did not differ from levels detected in non-stimulated cell cultures. Nitrite levels detected in supernatants of LPS-stimulated bighorn macrophage cultures treated with an inducible nitric oxide synthase (INOS) inhibitor, N(G)-monomethyl-L-arginine, were similar to that observed in non-stimulated cultures indicating a role for the iNOS pathway.

Impaired alveolar macrophage function in smoke inhalation injury

The high incidence of both bacterial pneumonia and the adult respiratory distress syndrome (ARDS) associated with smoke inhalation injury (SII) may result, at least in part, from smoke-induced injury to the alveolar macrophage (AM). Specifically, we hypothesized that AM antimicrobial function, ability to phagocytose apoptotic PMNs, and capacity to prevent apoptosis in PMNs are impaired by smoke. To test these hypotheses, AMs were harvested by bronchoalveolar lavage from sheep before and after the animal was exposed to cotton smoke. The two populations of AMs were incubated with Pseudomonas aeruginosa (PSA) in vitro. Normal AMs (NAMs) phagocytosed a mean of 99 +/- 11% of the PSA placed in their wells, whereas smoke-exposed AMs (SAMs) ingested only 60 +/- 8%. NAMs killed 80 +/- 8% of PSA ingested, whereas SAMs killed only 56 +/- 16% (P < 0.05). When sheep PMNs, allowed to undergo apoptosis, were incubated with the two AM populations, 66 +/- 3% of the NAMs and 40 +/- 6% of the SAMs demonstrated phagocytosis of these apoptotic PMNs (P < 0.05). Fresh sheep PMNs were incubated in unconditioned media, NAM and SAM-conditioned media, and followed over 48 hr for the development of apoptosis and maintenance of viability. The NAM-conditioned media markedly prevented apoptosis and augmented PMN survival relative to the unconditioned and SAM-conditioned media (P < 0.05). The poor antimicrobial function known to be characteristic of apoptotic PMNs, together with the directly impaired antimicrobial function of AMs, may contribute to the infectious complications of SII. If the PMNs recruited to the lung in SII are not properly supported by the AMs following smoke injury, large numbers may undergo apoptosis. If not properly disposed of by these SAMs, the apoptotic PMNs could eventually lyse, releasing tissue toxins, resulting in escalation of lung injury and leading to ARDS.

Comparison of arachidonate metabolism by alveolar macrophages from bighorn and domestic sheep

We have defined the metabolites of arachidonic acid (AA) secreted by alveolar macrophages (AMs) of bighorn sheep and domestic sheep in response to three agents: calcium ionophore A23187, phorbol myristate acetate (PMA), and opsonized zymosan. Cells were labeled with [3H]AA prior to stimulation and 11 tritiated metabolites, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and hydroxyeicosatetraenoic acids (HETEs), were detected and quantitated by high-performance liquid chromotography and radiometry. Zymosan stimulation resulted in the release of significantly elevated quantities (P less than 0.05), of LTB4, [5(S), 12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid], 5-HETE, [5(S)-hydroxyeicosatetraenoic acid], and the nonenzymatic isomers of LTB4, [LTB I, 5(S),12(R)-6-trans-LTB4] and LTB II, [5(S), 12(S)-6-trans-LTB4], from domestic sheep AM when compared to bighorn sheep AM. Phorbol myristate acetate (PMA) stimulation released significantly elevated quantities (P less than 0.04), of TXB2, (thromboxane B2), HHT, [12(S)-12-hydroxy-5,8,10-heptadecaenoic acid], LTB I, LTB II, and 15-HETE, [15(S)-hydroxyeicosatetraenoic acid] from domestic sheep AMs when compared to bighorn sheep AMs. However, after A23187 challenge, only 15-HETE was significantly elevated (P less than 0.04) in domestic sheep AMs when compared to bighorn sheep AMs. These clear differences in AA metabolism of AMs obtained from bighorn and domestic sheep in response to three different agonists suggest not only different control mechanisms for lung metabolism of AA in the two species, but also suggest that differences in the metabolites released may lead to quite different regulation of lung defense mechanisms in the two sheep species.