Rat haptoglobin: method of quantitation and response to antiarthritic therapy in collagen arthritis.

Concentrations of the acute phase reactant haptoglobin were quantitated in the serum of rats using a commercially available antihuman haptoglobin radial immunodiffusion kit. That this antiserum reacted with rat haptoglobin was shown through the techniques of Ouchterlony immunodiffusion and immunoelectrophoresis. Haptoglobin levels were increased seven days after immunization of rats with type II collagen plus incomplete Freund's adjuvant (ICFA) and peaked on day 14. However, even six weeks post-immunization the concentration of haptoglobin was elevated in arthritic rats. A significant correlation was observed between the concentration of serum haptoglobin and the severity of disease (arthritic index) in rats immunized six weeks previously with type II collagen plus ICFA. The effects of antiinflammatory and antirheumatic therapy on arthritic index and serum haptoglobin concentration were determined using a therapeutic dosing protocol. Under these conditions, the known antiarthritic effects of nonsteroidal antiinflammatory drugs, steroids and immunosuppressive agents in this model were confirmed. Of these agents, only the nonsteroidal drugs reduced serum haptoglobin; hydrocortisone, cyclophosphamide and azathioprine elevated haptoglobin. Aurothioglucose, auranofin, and chloroquine, members of the class of disease-modifying antirheumatic drugs, had a general tendency to exacerbate disease, but had minimal effect on serum haptoglobin. D-Penicillamine had little effect on arthritic index and haptoglobin. These results suggest that, while haptoglobin levels do correlate with the intensity of hindpaw swelling, measurement of haptoglobin may not be an accurate indicator of the underlying disease processes in the collagen arthritis model.