British Journal of Haernatologu. 1991. 79, 286-290

Elevated serum interleukin-6 levels in patients with reactive thrombocytosis W. HOLLEN,J A M E S HENTHORN, JAMES A. KOZIOLA N D SAMUEL A . BURSTEIN University of Oklahoma Health Sciences Center, Oklahoma City. Oklahoma, and Scripps Clinic and Research Foundation, La Jolla, California

CHARLES

Received 15 April 1991: accepted for publication 13 June 1991

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Summary. Interleukin-6 (IL-6) is known to promote megakaryocytopoiesis in vitro and raise platelet counts in vivo. To determine if there is a relationship between circulating IL-6 and thrombocytosis in man. we measured bioactive IL-6 in the serum of 13 patients with myeloproliferative disorders and 143 patients with reactive thrombocytosis having platelet counts 2 600 x 109/1. IL-6 activity was assayed using the IL-6-responsive B9 cell line. Seventy-one controls with normal platelet counts had a mean IL-6 level of 2.1 9 U/ ml f 1.08 (SD).None of the 1 3 patients with myeloprolifera-

tive disorders had elevated IL-6 levels ( 1 .56 U/ml f 1.2). In contrast, serum IL-6 levels of 143 patients (158 samples) with reactive thrombocytosis were significantly greater than controls (38.3 U/mlf94.6: P 2 SD (i.e. ~ 4 . 3 U/ml).

RESULTS The mean platelet counts and serum IL-6 levels of patients in the control cohort and the primary, reactive, and miscellaneous thrombocytosis categories are shown in Table I. The 143 patients with reactive thrombocytosis had higher serum levels of IL6 ( 3 8 . 3 f 9 4 . 6 U/ml) as compared with the 71 normal controls (2.19f 1.08 U/ml; P