The status of pulmonary host defense in the neonatal sheep: cellular and humoral aspects

Age-related changes in phagocytic activity and production of pro-inflammatory cytokines by lipopolysaccharide stimulated porcine alveolar macrophages

The aim of the present study was to determine the age-related changes of phagocytic capacity and the kinetic production of cytokines in lipopolysaccharide-stimulated porcine alveolar macrophages. For this purpose, AMs were isolated from 5 (newborn), 40 (post-weaned) and 120 (young) day old pigs. Results of phagocytosis assay showed that AMs from newborn piglets had less phagocytic capacity than those of young pigs (P<0.05). For the kinetics study, cells and supernatant were collected at 1, 6, 12, 24, 36 and 48 h after LPS stimulation for quantification of cytokine mRNA and protein by quantitative real-time PCR and ELISA, respectively. The kinetics results showed that AMs from newborn piglets were significantly less capable of producing IL1β, IL6, IL12β, TNFα and IL8 than post-weaned piglets or young pigs. IL18 mRNA did not show significant differences between ages. MIP2 and MCP1 mRNA was higher in young pigs. Hence, higher production of cytokines by AMs may be the surfactant factors in the pulmonary host defense system. These results indicate that AMs from newborn piglets might be functionally immature, which may lead to increased susceptibility to lung infections. Future studies of cytokine kinetics in more animals are clearly needed to confirm these results across a wider age range.

Expression of Toll-like receptors and downstream genes in lipopolysaccharide-induced porcine alveolar macrophages

The aim of the present study was to determine the age-related kinetic changes of Toll-like receptors (TLRs) and downstream genes expression, and secretion of cytokine in lipopolysaccharide (LPS) stimulated porcine alveolar macrophages (AM). For this purpose, AMs were isolated from 5-day-old newborn piglets and 120-day-old young pigs. mRNA expression and cytokine measurement was determined by quantitative real-time PCR and ELISA, respectively. First, AMs were incubated for 24 h in the absence or presence of increasing concentrations of LPS. Results showed the up-regulation of TLRs 2, 4, 5 and 9 mRNA from all concentrations of LPS used, as compared to non-stimulated cells, and TLR4 was the highest expression in both ages (P<0.05). Furthermore, quantitative analysis demonstrated increased expression of mRNAs encoding TLRs 2, 4, 5 and 9, LBP, CD14, MD2, MyD88, IRAK4 and TRAF6 in both ages in a time-dependant manner (P<0.05). Overall, LPS inducible mRNA for TLR4, LBP, CD14 and MyD88 had higher expression in newborn piglets compared with those of young pigs (P<0.05). The level of cytokine protein IL6 and TNFα in supernatant fluid significantly varied with time of incubation and age of animals. Their concentration increased immediately at 1 h after LPS stimulation and remained significantly higher up to 48 h in both ages. Production of pro-inflammatory cytokine protein IL6 and TNFα in supernatant was significantly higher in young pigs than those of piglets. This study suggests that differential age-related changes in the expression of TLRs and downstream genes, and pro-inflammatory cytokine could contribute to a different age-related innate immune response during pulmonary infection. Further investigation is warranted to determine the precise effects of LPS on porcine AMs by means of a functional study across a wider age range.

Age-dependent changes in porcine alveolar macrophage function during the postnatal period of alveolarization

During early postnatal ontogeny in most mammals, the lung is structurally and functionally immature. In some species with relatively altricial lung morphology, there is evidence of a coupling between functional maturity of the pulmonary cellular immune system and alveolar maturation. Herein, we examine changes in alveolar macrophage (AM) number and function occurring during alveolarization in a more precocial species, the pig, to determine if heightened oxidative metabolism and phagocytic ability is similarly delayed until completion of lung morphogenesis. We assessed cell differential in lavage fluid and evaluated two main functional parameters of AM phagocytic response, the generation of reactive oxygen species (ROS), and particle internalization. AM functional maturation occurred mainly during the first postnatal week: the proportion of AMs, ROS generation, and phagocytosis all increased significantly. These results suggest maturational improvement of the impaired AM-based pulmonary immune system of the neonate piglet occurs during the postnatal period of rapid alveolarization.

Passive and active components of neonatal innate immune defenses

Innate immune defenses are crucial for survival in the first days and weeks of life. At birth, newborns are confronted with a vast array of potentially pathogenic microorganisms that were not encountered in utero. At this age, cellular components of the adaptive immune system are in a naive state and are slow to respond. Antibodies received from the dam are essential for defense, but represent a finite and dwindling resource. Innate components of the immune system detect pathogen-associated molecular patterns (PAMPs) on microorganisms (and their products) by means of pattern-recognition receptors (PRRs). Soluble mediators of the innate system such as complement proteins, pentraxins, collectins, ficolins, defensins, lactoferrin, lysozyme etc. can bind to structures on pathogens, leading to agglutination, interference with receptor binding, opsonization, neutralization, direct membrane damage and recruitment of additional soluble and cellular elements through inflammation. Cell-associated receptors such as the Toll-like receptors (TLRs) can activate cells and coordinate responses (both innate and adaptive). In this paper, accumulated knowledge of the receptors, soluble and cellular elements that contribute to innate defenses of young animals is reviewed. Research interest in this area has been intermittent, and the literature varies in quantity and quality. It is hoped that documentation of the limitations of our knowledge base will lead to more extensive and enlightening studies.