Mycobacterium Tuberculosis Infection of the Placenta: A Study of the Early (Innate) Inflammatory Response in Two Cases

Infections with Mycobacterium tuberculosis (MTb) are globally prevalent in many countries, yet descriptions of placental pathology in tuberculous patients are scanty. The usual necrotizing granulomatous response associated with tuberculous infections requires an activation of the adaptive immune system. However, before this system is turned on, the 1st encounter with the tubercle bacillus is mediated by the innate immune system. This pathway utilizes innate surface receptors in neutrophils and histiocytes predominantly and does not produce a granulomatous pattern of inflammation. In this report we describe 2 cases of placental involvement with MTb in which an acute abscess-like inflammatory response with Myeloperoxidase and CD68-positive neutrophils and histiocytes causing acute villitis and intervillitis, with abundant acid-fast mycobacteria, were identified. Other cellular markers consistent with adaptive immunity were negative. These nongranulomatous lesions are seen in primary tuberculous infections occurring in a naïve woman and, obviously, a naïve fetus. These cases with early response inflammation in the placenta are frequently missed precisely because the mother is not known to be infected or has been recently diagnosed and because the symptoms in the newborn may not develop for several weeks, by which time the placenta may have been discarded. This report also shows that the differential diagnosis of acute villitis and intervillitis in the placenta should include tuberculosis aside from the more common bacterial infections such as listeriosis.