Boophilus microplus: cellular responses to larval attachment and their relationship to host resistance.

The histology of early feeding lesions of the cattle tick B. microplus has been studied using 32P labelled larvae to standardize the duration of attachment. Critical studies were made on 3-h lesions in six separate experiments on different groups of British breed animals. Each group consisted of three animals--one previously unexposed to ticks, one of high resistance and one of low resistance. The degree of mast cell disruption, eosinophil concentration and degranulation, and the extent of epidermal vesiculation were all significantly greater at the site of attachment on highly resistant hosts. In previously unexposed animals there was no mobilization of eosinophils nor mast cell breakdown and no epidermal vesiculation. Possible immune mechanisms producing mast cell disruption and the infiltration and concentration of eosinophils are suggested, and the effect of eosinophil degranulation on larval attachment and feeding is discussed.