Infestation of larval Haemaphysalis longicornis ticks induced a threefold increase of eosinophils in the peripheral blood of normal WBB6F1- +/+ mice 2 days after
tick infestation. In genetically mast cell-deficient WBB6F1- W/Wv mice, a threefold increase of blood eosinophils was observed 6 days after the
tick infestation. However, marked infiltration of eosinophils was detected in the
tick infestation sites of the WBB6F1- +/+ mice but not the WBB6F1- W/Wv mice. When the mast cell deficiency of WBB6F1- W/Wv mice had been rescued locally by
intradermal injections of WBB6F1- +/+ mouse-derived cultured mast cells, a rapid increase of blood eosinophils and tissue infiltration of eosinophils were revealed following
tick infestation. The intravenous (i.v.) injection of immune spleen or lymph node cells obtained from WBB6F1- +/+ mice 10 days after
tick infestation led to significant
eosinophilia in naive recipient mice. Treatment with anti-Thy-1.2 or anti-CD4
monoclonal antibody (mAb) and
complement (C) completely abolished the
eosinophilia; the early response (2 days after tick challenge) is dependent on mast cells at the feeding site, and the late response (6 days after tick challenge) is dependent on T lymphocytes. Since amplified
interleukin-5 (IL-5)
cDNA was detectable in the spleen cells 4 days after
tick infestation, the late response might be mediated by
IL-5. The infiltration of eosinophils at the feeding site of skin appeared to be dependent on mast cells.