Inhibitory effect of polyunsaturated fatty acids on apoptosis induced by Streptococcus pneumoniae in alveolar macrophages

BACKGROUND & OBJECTIVES Apoptosis is considered as a major defense mechanism of the body. Multiple pathogens induce macrophage apoptosis as a mode of immune evasion. In earlier studies, n-3 polyunsaturated fatty acids (PUFA) have been reported to be protective against neuronal apoptosis and neuronal degeneration, seen after spinal cord injury. In this study, we tried to evaluate the role of n-3 polyunsaturated fatty acids on the process of macrophage phagocytic activity and apoptosis in mice. METHODS Mice were divided into three groups (n=60); Group I was fed on sea cod oil; Group II on flaxseed oil supplementation for 9 wk along with standard laboratory chow diet. Group III was fed on standard diet and served as control. After supplementation, phagocytic and apoptotic (morphological staining: acridine orange plus ethidium bromide; H-33342 plus propidium iodide staining and DNA ladder formation) activities of mouse alveolar macrophages were assessed. RESULTS Alveolar macrophages (obtained from sea cod oil and flaxseed oil fed group mice) showed significant increase in bacterial uptake as well as intracellular killing (P 0.05) of Streptococcus pneumoniae. Significant decrease (P<0.05) in apoptotic cells was observed among alveolar macrophages from sea cod and flaxseed oil fed mice whereas maximum apoptosis was observed in control alveolar macrophages on interaction with bacteria in vitro which was confirmed by DNA laddering. INTERPRETATION & CONCLUSIONS These findings suggest that dietary supplementation with n-3 polyunsaturated fatty acids to mice led to enhanced phagocytic capability of their alveolar macrophages as well as provided protection against apoptosis upon challenge with S. pneumoniae.