This study will gather information on the safety of FolateScan and the ability of FolateScan to detect inflammation in the joints and other organs in people with arthritis (rheumatoid arthritis and osteoarthritis), systemic lupus erythematosus, multiple sclerosis, interstitial pneumonitis, Crohn's disease as well as in healthy persons without these conditions.

The folate receptor is over-expressed on many types of cancer cells and in RA models, and new folate receptor targeted therapies are being developed to target cancer cells that over-express the folate receptor. As with other targeted therapies, it is important to develop diagnostic tests that will provide accurate information on folate receptor status and aid in selecting patients that may benefit from folate-targeted therapy.

EC20 concentrates in the extremities and liver and spleen of rats with adjuvant induced arthritis. The increased uptake is mediated by overexpressed folate receptor on macrophages, and the intensity of the uptake is greatly reduced by addition of excess folate, supporting the specificity of the uptake. Depletion of macrophages greatly reduced folate receptor and abolishes uptake of EC20. This suggests that EC20 may be useful in assessing macrophage involvement in the active inflammatory process of RA, and perhaps other systemic immune mediated disorders as well.

FolateScan may allow the clinician to get accurate real-time data on receptor binding, in a less invasive manner, at all actively inflamed sites throughout the treatment regimen. This kind of information may help the physician make better clinical decisions regarding therapy, including folate targeted therapies.

Inclusion Criteria:

• Study will include 40 subjects with rheumatoid arthritis (active or inactive disease, defined as no swollen joints) and 5 patients in each of the following diagnosis: osteoarthritis, multiple sclerosis, Crohn's disease, systemic lupus erythematosus, interstitial lung disease and no autoimmune disease (healthy).
• Subjects must have disease duration of at least 6 months and creatinine level may not be greater than 1.5 mg/dL.

Exclusion Criteria:

• Subjects will be excluded if they are pregnant, have an active infection, received an investigational therapy in the past month or previous malignancy within the past 5 years.