Administration of specific goat anti-thymocyte serum (ATS) to rabbits, prior to a primary infestation by
Rhipicephalus appendiculatus larvae, blocked the acquisition of resistance significantly only in the third
infestation. The larvae which fed on these rabbits had higher engorgement masses than did those feeding
on untreated control rabbits. Also, a higher percentage (92%) of larval ticks fed on these animals
than on the controls (88%). ATS also induced a leucopenia due to a lymphopenia in the treated rabbits.
It was concluded that a T-cell-dependent component might be involved in acquired resistance to infestation
by R. appendiculatus.
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