Plasma thrombospondin levels in sheep with allergic asthma

Study objective: In search of a better universal marker of tissue inflammation in allergic reactions, we studied platelet activation and its relation to allergic asthma in sheep. Setting: University research laboratory. Subjects: Twenty-three allergic sheep. Design and interventions: We serially measured plasma thrombospondin (TSP), a glycoprotein secreted from activated platelets, using enzyme-linked immunosorbent assay with a monoclonal antibody. We validated the assay by establishing a standard curve that closely matches that of humans. Measurements and results: Of the 23 allergic sheep tested, 10 demonstrated early airway response (ER group) and 13 had early and late dual airway responses (DR group) to inhaled Ascaris suum antigen. TSP was measured before, and at 0, 1, 2, 3, 4, 6, 8, and 24 h postantigen challenge. Both groups showed an increase in plasma TSP level after antigen challenge, but only the DR group showed a significant increase in TSP at 1 h (threefold) and 8 h (sixfold) postchallenge. The two sheep that received carbachol challenge showed a slight rise in TSP at 8 h postchallenge. There was a significant correlation between the TSP level at 1 h and the peak early airway response in the DR group. Conclusions: These results suggest that the two groups of allergic sheep may have two distinct induction processes leading to airway obstruction. The dual peak rise in TSP level that coincided with the airway response also suggests that an early priming effect exists in the DR group, which might have led to the late response. We conclude that intravascular platelet activation often occurs in mast cell-mediated allergic disorders. Therefore, plasma TSP may be useful for monitoring the course of allergic disorders.