A protective "concealed" antigen from Boophilus microplus. Purification, localization, and possible function

A membrane protein that can be used successfully to vaccinate cattle against the tick Boophilus microplus has been purified and characterized. The mature protein, which is referred to as Bm91, has an apparent m.w. of 86,000, an isoelectric point of 4.8 to 5.2, and is glycosylated, with an affinity for lentil lectin. Bm91 is of relatively low abundance, with approximately 300 to 400 micrograms being recovered from 1 kg of semiengorged adult female ticks. The protein is located largely in the salivary gland and gut of these ticks. Partial amino acid sequence data for the protein show striking similarities to that of mammalian angiotensin-converting enzyme, suggesting that the Ag may have an enzymatic function. The protein seems not to be recognized by sera from cattle with extensive exposure to ticks under natural conditions. The immunity induced by vaccination, therefore, represents another example of vaccination against a hematophagous parasite with "concealed" Ags.