ABSENCE OF ACQUIRED-RESISTANCE TO NYMPHAL IXODES-RICINUS TICKS IN BALB C MICE DEVELOPING CUTANEOUS REACTIONS/

BALB/c mice underwent 3 successive infestations with 15 Ixodes ricinus nymphs. No resistance was acquired as assessed by evaluating tick att achment, duration of blood meal, weights of engorged nymphs, and molti ng success. However, the hosts developed cutaneous immediate- and dela yed-type hypersensitivity reactions when reinfested. Histological exam ination of tick attachment sites showed that inflammatory cells consis ting of neutrophils, eosinophils, and mononuclear cells (lymphocytes a nd monocytes) infiltrated the skin more intensively during reinfestati ons. The number of intact mast cells did not vary between successive i nfestations, whereas the number of degranulated mast cells increased i n the early stages of reinfestations. Basophils, which represent 12% o f total infiltrating cells, were only observed and quantified in the s kin of reinfested mice using transmission electron microscopy (TEM). D egranulating eosinophils were also observed by use of TEM.