Adjuvant arthritis in the rat. Distribution of fluorescent material after footpad injection of rhodamine-labelled tubercle bacilli.

Adjuvant disease in the rat may represent a cell-mediated response to tuberculous material disseminated from the original injection site, but previous studies have provided only indirect evidence for this dissemination. In the present experiments tubercle bacilli labelled in vitro with rhodamine isothiocyanate (RITC) were injected into a footpad as Freund's complete adjuvant. Serial studies showed two varieties of fluorescent material in the tissues (1) intracellular and extracellular intact and fragmented bacilli, and (2) amorphous intracellular material. Both types of material were identified in the injected foot and draining lymph nodes. Bacilli were also identified in the contralateral knee joint, peritoneum, pleura, lung, and liver, while amorphous material alone appeared in the spleen. The presence of intact bacilli was confirmed by positive Ziehl-Nielsen staining of the organisms, but the amorphous intracellular material did not stain positively by this method. The use of RITC-labelled organisms considerably reduced the severity of adjuvant disease. Most of the organisms identified in sites distant from the injected limb were not situated within foci of inflammation. Marked differences in processing of the tuberculous material (and lack of dissemination of intact bacilli) were noted when labelled organisms were injected in saline instead of in oil.