Ornithodorus tartakovskyi: quantitation and ultrastructure of cutaneous basophil responses in the guinea pig

Cutaneous lesions elicited in guinea pigs by primary and secondary feeding populations of the argasid tick, Ornithodorus tartakovskyi, were analyzed by light and electron microscopy. Small clusters of basophils appeared at primary bite sites within 24 hr of tick attachment, and by 72 hr constituted approximately 11% of the total leukocytes. Secondary feeding sites exhibited an augmented cellular infiltrate that was dominated by basophils at all times (48-56% of total cells). Eosinophil proliferation was minimal, however, and the remaining cells were of the mononuclear type. Despite mounting a strong cutaneous basophil response of the kind that mediates immune rejection of prolonged-feeding ixodid ticks, the guinea pigs showed no resistance to the fast-feeding Argasidae. It is suggested that argasid ticks probably complete their blood meal prior to basophil arrival at the bite site. Electron microscopy indicated that the number of epidermal Langerhans cells increased with time in both primary and secondary lesions; these cells were more numerous in challenge infections however, and seemed also to occur in the dermis. Basophils at secondary bite sites exhibited three kinds of structural alterations classified as: (1) piecemeal alterations--involving a vesicular degranulation mechanism; (2) an anaphylactic-type of alteration--involving single or compound exocytosis of whole granules; and (3) cytotoxic alterations culminating in complete disintegration. The majority of basophils in 72 hr secondary lesions exhibited cytotoxic alterations. It is suggested that such changes result from contact with tick-derived toxins or enzymes.