Morphometry and DNA analysis of midgut digestive cells of Ixodes sinensis after infesting rabbits

The morphometry of midgut digestive cells of female Ixodes sinensis Teng after infesting rabbits with or without special immunity were analyzed by stereological methods. The DNA content of the cells was also determined by an image analyzer to explore the mechanism of host immunity against tick. The results showed that the midgut of ticks feeding on vaccinated animals enlarged with its wall thickened, the number and volume of digestive cells increased, and the DNA content rose along with the progression of tick feeding. In the group of the second infestating ticks (SI), changes of midgut were not as evident as those in the first infesting group (FI). It is suggested that the host rabbit can produce immune responses against the tick after its infestation causing destruction and exfoliation or inhibited proliferation of digestive cells in ticks. The normal digestive physiology of ticks in those immunized groups, especially in the 105kDa purified whole tick antigen vaccinated animal group (PA), was not as evident as those in the adjuvant control group (AC). The sectional number of digestive cell was reduced to less than 1/2 of that of AC group. The intensity of resistance to tick infestation was in the order PA>MA>SGA>CA. The results from the egg antigen group (EA) were similar to those of the AC group. All these indicated that the infestation of I. sinensis could induce effective resistance of the host against the tick by destroying its midgut digestive cells. Vaccination by antigens, i.e. 105kDa purified whole tick antigen, midgut antigen, salivary gland antigen, and crude whole tick antigen but not egg antigen, produced specific resistance against infestation. The 105kDa purified whole tick antigen was proved to be the most effective one and may serve as the choice of vaccine.