T cell lymphoid aggregates in bone marrow in idiopathic hypereosinophilic syndrome.

Idiopathic hypereosinophilic syndrome (HES) comprises a heterogeneous group of disorders characterised by prolonged eosinophilia with no obvious cause. A patient with longstanding HES is reported in whom unusual non-neoplastic peritrabecular lymphoid aggregates were present in the bone marrow, a hitherto undescribed association, as far as is known. An eosinophil colony stimulating activity was detected in the serum. The findings in this patient provide further evidence for an important role for eosinophil colony stimulating activity interleukin-5 mediated T lymphocyte control of eosinophil production in the pathogenesis of the HES.