Folate-targeted immunotherapy reduces folate receptor expressing macrophages in inflamed tissue of AIA rats. (a) The level of folate receptor (FR)+ activated macrophages in the limbs of non-immunized (Folate-fluorescein isothiocyanate [FITC]) and keyhole limpet hemocyanine (KLH)-FITC-immunized AIA rats (KLH-FITC + Folate-FITC [FTI]) 25 days after initiation of treatment with folate-FITC was determined 4 hours after i.p. injection of 0.5 mg EC20. Folate-FITC was administered at 375 nmole/kg twice a week until day 23, and estimates of FR+ macrophage numbers were made by weighing and counting the limbs for EC20 radioactivity (± standard deviation for n = 5 rats/group; [folate-FITC] vs. [KLH-FITC + folate-FITC (FTI)], p < 0.001). (b) Histological analyses were conducted to obtain a visual assessment of the abundance of ED1+ macrophages remaining in the inflamed soft joint tissue of the ankle joints (inflamed soft tissue adjacent to bone) of AIA rats immunized with KLH-FITC and then treated with either phosphate-buffered saline (PBS) alone (KLH-FITC) or folate-FITC (KLH-FITC + Folate-FITC [FTI]). Representative images from the joint tissue of two PBS-treated and two folate-FITC (FTI)-treated rats are shown (n = 5 rats/group).