Inverse correlation of interleukin-6 with soluble interleukin-6 receptor after transplantation of bone marrow or peripheral blood stem cells.

The relationship between interleukin-6 (IL-6) and the soluble interleukin-6 receptor (sIL-6R) was analyzed in 1481 serum samples of 82 patients after bone marrow or peripheral blood cell transplantation. The cytokine and its soluble receptor were measured on a daily basis starting at day -3 before and ending at day 21 after transplantation. IL-6 serum levels increased after transplantation, were at a maximum at day 6 and returned to the baseline level thereafter. The levels of sIL-6R showed an inverse course with a minimum at day 6. Statistical analysis revealed a strong inverse correlation between IL-6 and sIL-6R with a weighted Spearman rank correlation coefficient of -0.53 (P < 0.001). IL-6 may play a role in the decrease of sIL-6R either by the direct inhibitory effect on the expression of the IL-6R gene or by formation of IL-6/sIL-6R complexes followed by their internalization in target cells.