Cellular response in the tick feeding site in crossbred cattle artificially infested by Rhipicephalus microplus

Ticks and tick-borne diseases are of global importance and can cause serious economic losses to cattle-raising businesses. However, only few attempts have been made to describe the relationships between various cellular immune components and tick counts of, and therefore resistance to, Rhipicephalus microplus. The present study evaluated the late inflammatory cellular response and dermal dendritic cells at the attachment site in naturally presensitized bovines, artificially infested by R. microplus ticks. Twenty-two crossbred (Holstein × Gir) male experimental cattle were artificially infested with approximately 10,000 larvae of R. microplus. Parasitic infestation was determined by counting the engorged female ticks (4.5-8.0 mm in diameter) at the 21st day after artificial infestation. Biopsies (6 mm) were taken prior to the infestation and along with the tick count from the right pinna of each animal, and examined with histological techniques and immunohistochemistry using S100 protein. Inflammatory cell counts were conducted in the sections stained with the May-Grünwald Giemsa technique, and immunostained dermal dendritic cells were evaluated and classified in scores ranging from 0 to 4. An average of 39.2 ticks per animal was found. Eosinophils (47.8%) constituted the major portion of the cellular infiltrate, followed by mononuclear cells (28.3%), neutrophils (14.4%), and basophils (0% to approximately 2%). The dendritic cell count shows a considerable population in the dermis, with pre- and post-infestation mean scores of 1.54 and 1.89, respectively; these scores were not significantly different. Our results pointed out the importance of the cellular response in the cattle resistance to ticks.