Immunofluorescent staining of Treponema pallidum and Treponema pertenue in tissues fixed by formalin and embedded in paraffin wax.

The main problems in identifying Treponema pallidum in tissues are optical definition contrast, and specificity. In general, fluorochrome staining provides optical definition and contrast superior to that obtained by ordinary tinctorial staining, and in theory improved resolution. Specificity is lacking however, as with other stains. In contrast, immunofluorescence should combine the optical advantages of fluorochrome staining with the immunological advantages of specificity. Since the validity of such staining depends in part upon the integrity of the antigenic components of the micro-organisms, it is customary to avoid such drastic procedures as are involved in routine fixation and paraffin embedding. The manipulation, however, of unfixed cryostat material, in contrast with that of paraffin sections suffers from two disadvantages--namely, friability and infectivity. Published and unpublished work has shown antigenic stability in T. pallidum to a variety of procedures, both physical and chemical. Consideration of these facts led in this work to successful immunofluorescent staining after routine formalin fixation and paraffin embedding of tissues infected with T. pallidum or Treponema pertenue. Optical definition and contrast, were superior to that obtained with silver methods, but it was not possible to differentiate between these two organisms. Nevertheless immunofluorescence applied as described to paraffin sections should supply a convenient safe, and sensitive means of reappraising the histopathology of treponemal disease in patients, necropsy material, and experimental animals.