In vitro generation of hydrogen peroxide and of superoxide anion by bovine polymorphonuclear neutrophilic granulocytes,blood monocytes,and alveolar macrophages

Studies were conducted to compare the capacity of bovine blood monocytes, polymorphonuclear granulocytes (PMNs), and alveolar macrophages (AMs) to generate hydrogen peroxide and Superoxide anion. Following stimulation with opsonized zymosan, bovine PMNs respond with an immediate and vigorous liberation of both oxygen species, generating 4.7 ± 0.3 nmol H₂O₂/10⁶ cell and 12.3 ± 1.8 nmol O₂^–/10⁶ cell during the initial 15 min. This is more than twice the amount generated by AMs (1.2 nmol H₂O₂/10⁶ cell; 2.5 nmol O₂/10⁶ cell) and blood monocytes (0.5 nmol H₂O₂/10⁶ cell; 2.1 nmolO₂^–/10⁶ cell) during the same period. However, AMs continue generating H₂O₂ and O₂ at a steady rate for a longer period and consequently produce amounts equal to those of PMNs when measured over a longer time span. Also, AMs can be stimulated with nonopsonized zymosan in contrast to PMNs. However, the AM population appears to comprise at least two subpopulations, which can be clearly distinguished by their capacity for generation of reactive oxygen species, and which correlate with their tendency for adherence to a plastic surface. In contrast to what has been found in other species, the bovine phagocytes were found to lack receptors for tuftsin and formylated oligopeptides, and thus remained unresponsive to these compounds. The in vitro activity of the three cell types was found to be very dependent on culture conditions, such as cell density and an adherent versus suspended state. In addition, a comparison with macrophages and PMNs elicited into the mammary gland suggest that in vivo factors can significantly influence the in vitro activities. The mammary gland cells have lower activity than blood and alveolar cells, even though they have been primed by chemotactic factors), and this is probably caused by milk components, i.e., the microenvironment. Our observations are discussed with respect to the results obtained from different laboratories, different species, and different cell types; emphasis is placed on the problem of drawing conclusions about in vivo functions of cells from parameters assayed in vitro.