Anemia in monkey collagen-induced arthritis is correlated with serum IL-6, but not TNFα

We characterized the anemia in monkey collagen-induced arthritis (CIA) to evaluate whether this model is useful to analyze the basis of an anemia of inflammatory diseases. Cynomolgus monkey was immunized with bovine type II collagen on days 0 and 21. Blood samples were collected regularly and hematological parameters, biochemical parameters and cytokine levels were monitored. Red blood cell (RBC) counts, hematocrit (Ht), and hemoglobin (Hb) gradually decreased after immunization and reached the bottom on day 35. CRP rose rapidly after first immunization and reached a peak on day 21. Serum iron levels and transferrin (Tf) saturation were dropped after immunization and reached a bottom on day 28. Thereafter it returned to normal. On the other hand, ferritin levels increased after immunization. IL-6 levels showed positive correlation with CRP, and negative correlation with Hb, RBC counts and serum iron, but TNFα did not show any correlation. In conclusion, the anemia in monkey CIA is very similar to human anemia of inflammatory diseases concerning the changes of serum parameters. And our data strongly suggest that IL-6 is an essential cytokine for the development of the anemia in monkey CIA.