The Preliminary Study Of The Influence Of Candida On Innate Immune Response And Autophagy In Macrophages

Candida ranks as one of the most important cause of fungal infections.Macrophages play essential roles in innate immune system.Our study mainly focuses on the immune response against Candida species in macrophages,and is divided into two parts.Intraperitoneal injection of C.albicans led to increased macrophages in the abdominal cavity,and macrophages kept being the largest number of immune cells to swallow C.albicans after injection for 4 hours.These results reveal that macrophage is the main cell to bear the responsibility of phagocytosis of C.albicans.After the injection of Clodronate liposome,most of macrophages were eliminated,and mice infected by Candida albicans lose weight quickly and the mortality rate was increased,which proved the key role of macrophage in defense against C.albicans.Dectin-1,a C-type lectin receptor(CLR)is highly expressed on the surface of phagocytes and is considered as the key receptor for ?-glucan.After the transfection with siRNA-Dectin-1 to decrease the expression of dectin-1,we found Dectin-1 makes a unique contribution to phagocytosis of C.albcians in macrophages.It was reported that Dectin-1 participated in the recognition of C.albicans.Recently,the numbers of Candida infections due to non-albicans species like C.parapsilosis and C.tropicalis have been increasing.Our results showed that C.parapsilosis and C.tropicalis induced increased level of IL-6 and TNF-a in human PBMCs and THP-1 macrophage-like cells,and the inflammation response was characterized by the activation of dectin-1,NF-?B,p38 MAPK and ERK1/2 MAPK signaling pathways.These findings may partly explain how C.parapsilosis and C.tropicalis infection facilitates the inflammation,and contribute to the development of better therapies to control disease.Despite the inflammation induced by Candida,we investigate the relationship between Candida and autophagy in macrophages.In this study,we found that C.albicans inhibited LC3 turnover in THP-1-derived macrophages and RAW 264.7 cells with the treatment of several lysosomal inhibitors,including E-64d+pepstatin,chloroquine(CQ),NH4C1 and baflomycin-Al(BAF-A1).After the phagocytosis of C.albicans in macrophages,we observed fewer acridine orange-positive vacuoles and RFP-GFP-LC3 puncta without co-localization of phagocytized C.albicans.However,phagocytosis of C.albicans led to LC3 recruitment,but p62 and ATG9A didn't co-localize with LC3 or C.albicans.By combining MTOR inhibitors like rapamycin,Torin 1 and pp242,we found that these effects of decreasing autophagy flux were due to an MTOR-independent pathway.Nevertheless,we found that the C.albicans pathogen-associated molecular pattern ?-glucan increased LC3 turnover.In addition,phagocytosis of C.albicans caused a decrease in BrdU incorporation.Blocking autophagic flux aggravated this effect.Our finding suggests that phagocytosis of C.albicans decreases autophagic flux but induces LC3-associated phagocytosis(LAP)in an MTOR-independent manner in THP-1-derived macrophages.Occupation of LC3 by recruiting engulfed C.albicans might contribute to the inhibition of basal autophagic flux.Our study highlights the coordinated machinery between canonical autophagy and LAP that defends against C.albicans challenge.The role of autophagy in the anti-Candida immune ressponse needs to be clarified in macrophages.