Cutaneous basophil associated resistance to ectoparasites (ticks). Electron microscopy of Rhipicephalus appendiculatus larval feeding sites in actively sensitised guinea pigs and recipients of immune serum.

Electron microscopy has been used to monitor cellular activity in dermal lesions elicited by larval Rhipicephalus appendiculatus feeding on actively sensitised guinea pigs and recipients of immune serum. The early primary response is characterised by mononuclear cells, many of which appear to be activated fibroblasts. Collagen deposition is enhanced as the reaction progresses. Granulocytes of all types appear in the lesion between 18 and 96 hr but they show no evidence of degranulation. Free, membrane-bounded eosinophil and basophil secretion granules may, however, be identified in the dermis at day 5 or 6, but they seem to be liberated as a consequence of cellular disruption, rather than active degranulation. Some feeding sites resume a normal morphology by day 7. Lesions induced in actively sensitised hosts by a secondary feeding tick population are dominated by basophils. These cells begin to infiltrate the dermis within 6 hr and they show evidence of anaphylactic degranulation at 12 hr. Maximal release of membrane-free secretion granules occurs at about 18 hr post-attachment, at which time eosinophils become prominent. Degranulating basophils show a reduction in numbers from 24 to 96 hr, and phagocytic macrophages ingest residual granules and cellular debris. Guinea pigs sensitised with immune serum and subjected to challenge exhibit lesions similar to but less dramatic than those of actively sensitised and challenged animals. Anaphylactic degranulation of basophils occurs both in the dermis and within blood vessels. The immunological consequences of these events are discussed in relation to other models of cutaneous basophil hypersensitivity.