Tick-susceptible 'Bos taurus' cattle display an increased cellular response at the site of larval 'Rhipicephalus (Boophilus) microplus' attachment, compared with tick-resistant 'Bos indicus' cattle

Abstract

Cattle demonstrate divergent and heritable phenotypes of resistance and susceptibility to infestation with the cattle tick 'Rhipicephalus (Boophilus) microplus'. 'Bos indicus' cattle are generally more resistant to tick infestation than 'Bos taurus' breeds although large variations in resistance can occur within subspecies and within breed. Increased tick resistance has been previously associated with an intense hypersensitivity response in 'B. taurus' breeds; however, the mechanism by which highly resistant 'B. indicus' cattle acquire and sustain high levels of tick resistance remains to be elucidated. Using the commercially available Affymetrix microarray gene expression platform, together with histological examination of the larval attachment site, this study aimed to describe those processes responsible for high levels of tick resistance in Brahman ('B. indicus') cattle that differ from those in low-resistance Holstein–Friesian ('B. taurus') cattle. We found that genes involved in inflammatory processes and immune responsiveness to infestation by ticks, although up-regulated in tick-infested Holstein–Friesian cattle, were not up-regulated in Brahman cattle. In contrast, genes encoding constituents of the extracellular matrix were up-regulated in Brahmans. Furthermore, the susceptible Holstein–Friesian animals displayed a much greater cellular inflammatory response at the site of larval 'R. microplus' attachment compared with the tick-resistant Brahman cattle.