Mast cell response during the early phase of tuberculosis: an electron-microscopic study

Guinea pig lungs were infected with Mycobacterium tuberculosis by intratracheal route and examined under electron microscope to investigate the morphological alterations of the organisms, if any, and the response of the host tissue. The bacilli showed no changes in their morphology, while the host tissues revealed several cells containing many electron-dense intracytoplasmic granules. These cells were predominantly seen during the 1st week of infection. The electron-dense bodies of these cells may be the ones observed by earlier workers and suggested to be the altered forms of tubercle bacilli. The present investigation, however, revealed them to be the granules of the mast cells. These cells were observed to respond to tuberculous infection during the first few days by appearing in large numbers crowded with intracytoplasmic granules and soon disintegrating as the result of subsequent degranulation. The above observation is presented and its significance discussed.