Allergic Horses Research Articles

PAF- and LTB4-induced migration of eosinophils and neutrophils isolated from horses with allergic skin disease

Platelet activating factor (PAF) and leukotriene (LT)B4 cause thein vitro migration of equine granulocytes. In this study eosinophils and neutrophils have been prepared from horses showing clinical signs of the allergic skin disease sweet itch. Migratory responses have been compared to those of cells from normal animals. Cell migration was measured in a 48-well microchemotaxis chamber. PAF and LTB4 caused the migration of neutrophils and eosinophils from both allergic and normal horses. However, responses of eosinophils, but not neutrophils, from allergic horses were significantly reduced (p<0.05,n=5). No difference was observed between the random movement of neutrophils or eosinophils from normal and allergic horses. These results suggest that the migratory responses to PAF and LTB4 of eosinophils from allergic horses are down-regulated.

Duration of antigen‐induced hyperresponsiveness in horses with allergic respiratory disease and possible links with early airway obstruction

Antigen-induced airway hyperresponsiveness in allergic horses has previously been demonstrated when clinical signs of acute airway obstruction were apparent, as a consequence of exposure of animals to hay and straw for variable periods of time, and repeat measurements of hyperresponsiveness have been made no earlier than 1 week after challenge. In the present study airway responsiveness to methacholine has been measured in normal horses and allergic horses in clinical remission before and 24, 48 and 72 h after a hay and straw challenge of fixed, short, duration (7 h). Correlations between early increases in interpleural pressure and hyperresponsiveness have also been investigated. As in other studies, the mean airway responsiveness of groups of normal and allergic horses in clinical remission was not significantly different. The responsiveness to methacholine of allergic, but not normal, horses was increased after antigen challenge and was significantly greater than that of normal horses at 48 and 72 h after challenge (log PD8 cm: -0.77 +/- 0.28 vs. 0.27 +/- 0.14 at 48 h and -0.6 +/- 0.25 vs. 044 +/- 01 at 72 h; P < 0.05). There was also a significant correlation between interpleural pressure at the end of the 7-h challenge in allergic horses and the increase in responsiveness to methacholine at 24, 48 and 72 h. These results demonstrate that antigen induces an increase in airway responsiveness in allergic horses that persists for up to 3 days and which may be linked to the initial increase in interpleural pressure.

Early neutrophil but not eosinophil or platelet recruitment to the lungs of allergic horses following antigen exposure.

Previous studies have shown that bronchoalveolar lavage fluid from horses with allergic respiratory disease and showing clinical symptoms contains increased numbers of neutrophils. In some cases, the eosinophil count is also increased. In this study the time course of changes in lung function and the accumulation of radiolabelled leucocytes and platelets in the lungs of allergic and normal horses has been examined during a 7 hr allergen exposure. Antigen challenge had no effect on pleural pressure or the distribution of radiolabelled neutrophils, eosinophils or platelets in normal horses. In contrast, in 6/8 allergic horses, there was an increase in pleural pressure and neutrophil accumulation in the lungs, both of which were evident after 4-5 hr. However, during the 7 hr challenge period radiolabelled eosinophils were detected in the lungs of only 1/6 horses exhibiting an increase in pleural pressure and in 1/7 horses that failed to show a change in airway function despite a clinical history of allergic respiratory disease. Antigen challenge did not alter the distribution of radiolabelled platelets in the five allergic horses tested. These results demonstrate that increased pleural pressure is not accompanied by eosinophil or platelet accumulation in the lungs of horses with allergic respiratory disease following exposure to antigen. However, changes in airway function can be associated with neutrophil accumulation but can also take place in the absence of this cell recruitment. This raises the possibility that the presence of neutrophils in the lung is not a prerequisite for changes in lung function.

Epidemiological and immunological studies of sweet itch in horses in Israel.

A survey of sweet itch in horses in Israel based on a questionnaire to owners reported that 158 of 723 horses (21.8 per cent) had sweet itch lesions. The results indicated that the likelihood of a horse acquiring sweet itch decreased with increasing altitude but no definite association with rainfall zones was evident. Variation in the density of the horse population, however, obscured these observations. In the population surveyed, stallions were more sensitive than mares and pale horses appeared to be less sensitive than dark ones, but the sample size of this latter group was much smaller. Intradermal injection of extracts of Culicoides imicola and Stomoxys calcitrans gave immediate reactions in sensitive horses but delayed reactions were observed only with extracts of C imicola. Sensitivity to extracts of C circumscriptus was also evident in allergic horses. Antibodies to extracts of Culicoides species and Stomoxys species were demonstrable in the serum of normal and allergic horses by the ELISA technique.