Progressive sensitization of circulating basophils against Ixodes ricinus L. antigens during repeated infestations of rabbits

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Abstract
The sensitivity of rabbit basophils to antigens from I. ricinus females was studied by a degranulation test. Observations of basophil numbers and degranulation were made on the 6th day of each of 4 sequential infestations. Maximal degranulation of cells was observed after challenge of cells with antigen at a concentration of 106 and 107 pg/ml. At these concentrations, during a 1st infestation, 21.8 and 23.6% of cells degranulated. During a 2nd infestation, these percentages increased (34.8 and 33.8%) and reached 59.8 and 63.8% by the 4th infestation. A plasma factor which partially blocks basophil degranulation, is described. This was already present during the 1st infestation, since in its presence the percentage of degranulation was reduced by 2.8 and 4.0%, respectively, on challenge with 106 and 107 pg antigen/ml. Inhibition was maximal at the 4th infestation (difference: 16.5 and 20.5%). Basophil sensitization and inhibition of the degranulation are thus both progressive phenomena. After 10-15 infestations on 4 other rabbits, 75.0 and 79.8% degranulation was obtained. The inhibition of degranulation by plasma was also greater (difference: 25.5 and 27.4%). IgG specific anti-I. ricinus antibodies were identified by indirect immunofluorescence. In 2 animals, they were detected at the 6th day of the 1st infestation. Subsequently they were generally present for all the animals.