Neutrophil migration induced by equine respiratory secretions, bronchoalveolar lavage fluids and culture supernatants of pulmonary lavage cells

Supernatants of equine respiratory secretions enhanced the migration of equine neutrophils into the lower compartments of Boyden chambers. Checkerboard analysis revealed that the neutrophil migration promoting activity (NMPA) of secretion specimens was in great part caused by chemokinesis, irrespective of the neutrophil score of the specimen. The NMPA of respiratory secretions was correlated neither with the neutrophil score of the secretion specimen nor with the severity of the chronic pulmonary disease. Respiratory secretions collected while horses were kept under low dust or under dusty housing conditions induced migration of neutrophils in the same order of magnitude. The number of migrated neutrophils and the procoagulant activity (PCA) within respiratory secretion specimens was positively correlated; however, the meaning of this finding is not yet clear. None of the nine cell-free supernatants of bronchoalveolar lavage fluid, which were assayed undiluted, induced significant neutrophil migration, although some samples contained up to 4.0 x 10(5) neutrophils/ml. In vitro culture of lung lavage cells, which mainly comprised macrophages and lymphocytes, without stimulation or with the addition of low doses of phytohemagglutinin (PHA) resulted in the secretion of NMPA which was in great part chemotactic. However, culture supernatants of lung cell preparations which were stimulated by lipopolysaccharide (LPS) or by PHA-prestimulated lymphocytes reduced the migration of neutrophils compared with the supernatants of control cells. NMPA within culture supernatants had a highly significant negative correlation with the PCA of macrophages within the lung cell preparations. Our results imply that a complicated and sophisticated regulation underlies neutrophil accumulation within the airways of horses affected with chronic pulmonary disease. Future experiments are required to assess the biological significance of the factors modulating neutrophil migration which are present in the respiratory secretions and in the culture supernatants of equine lung lavage cells.