Encephalitozoon cuniculi (Microsporidia) suppresses apoptosis in human macrophages (133.12)

Abstract

Abstract Microsporidia are fungi-related, obligate intracellular parasites. Members of the genus, Encephalitozoon, are clinically important as causes of emerging and opportunistic infections associated with diarrhea and systemic disease. E. cuniculi replicates within macrophages and is believed to disseminate via trafficking monocytes/macrophages. Little is known about how microsporidia survive within macrophages. To address this, the affect of E. cuniculi infection on the ability of macrophages to undergo apoptosis was evaluated. Cultures of human THP-1 macrophages were inoculated with live or dead E. cuniculi (2:1 spores to cells). After 1, 2, 4, and 8 days, the cultures were induced for apoptosis with staurosporine (50 ng/ml) for 4 hours and assessed via TUNEL. Macrophages inoculated with live spores exhibited 1.8-, 3.1- and 3.2-fold less apoptosis than those inoculated with dead spores after 1, 2 and 4 days, respectively. After 8 days, macrophages inoculated with live spores exhibited signs of rupture due to infection and displayed only a 1.64-fold reduction in TUNEL-positive cells compared with macrophages given dead spores. Caspase 3 activity associated with apoptosis was measured on day 4 and was 4.3-fold lower in macrophages treated with live spores compared with those inoculated with dead spores. These early results suggest that E. cuniculi may inhibit apoptosis of macrophages to prolong their survival within these cells. This research was supported by funding from the N.I.H. (RR00164 and AI071778).