Sarcoidosis, once thought to be a variant of
tuberculosis, is currently listed as a disease of unknown etiology. The present study was initiated by unpublished observations that Schaumann bodies-the laminated inclusions often encountered in sarcoid
granulomas-cross-reacted with commercial polyclonal
antibodies to Mycobacterium bovis, Mycobacterium duvalii and Mycobacterium paratuberculosis. Given the broad cross-reactivity of many mycobacterial
antigens, those findings lacked specificity but warranted in depth probing of the immunoprofile of the bodies, particularly for specific mycobacterial
antigens.
Formalin-fixed tissue from eight patients with an established diagnosis of
sarcoidosis was studied with panels of
antibodies against both common cytoplasmic
proteins and various mycobacterial
antigens, using a labeled
streptavidin-
biotin-
alkaline phosphatase technique. Our findings indicate that Schaumann bodies are indeed residual bodies of heterophagic mycobacterial derivation. They immunostained intensely for the
lysosomal proteins muramidase and CD68, variably for some
cytoskeletal proteins (
tubulin,
desmin,
vimentin) and not at all for
cytokeratin, muscle actin, alpha-1-antichymotrypsin and
ferritin. Both cross-reactive and species specific
antigenic determinants of M.
tuberculosis complex were shown to be present. Affinity absorption with killed intact bacilli H37 Rv resulted in virtually equal loss of binding by all polyclonal antimycobacterial
antibodies to cross-reactive
ligands in Schaumann bodies. In addition, the bodies were clearly labeled with the
monoclonal antibodies TB68 and TB71, known to recognize species specific
epitopes of Mycobacterium tuberculosis complex. Although obtained on a small number of cases, our findings uphold Schaumann's original postulate that the laminated calcific inclusions represent remnants of "transformed tubercle bacilli".