Ex vivo observation of Pythium insidiosum-antigen treated neutrophils on three Pythium insidiosum strains isolated from vascular pythiosis patients

The mechanisms of Pythium insidiosum-antigen (PIA) immunotherapy activating a patient's immune system are unknown. We evaluated the interleukin-8 (IL-8) serum levels during P. insidiosum infection and after vaccination with PIA in vascular pythiosis cases. Furthermore, we studied the anti-P. insidiosum activity of neutrophils stimulated with various concentrations of PIA ex vivo in 3 strains of P. insidiosum isolated from vascular pythiosis patients. IL-8 serum levels were evaluated using the ELISA technique. We assessed the effect of PIA-stimulated neutrophils on the viability of zoospores using MTT assay, visualized neutrophil extracellular trap (NET) formation via microscopy, and measured the levels of double-stranded DNA (dsDNA) using PicoGreen dsDNA quantitation assay in 3 strains of P. insidiosum isolated from vascular pythiosis patients. Serum levels of IL-8 gradually lowered from the early to the end phases of vaccination with PIA among the surviving group of vascular pythiosis cases. Neutrophils stimulated with 0.01 µg/ml PIA reduced zoospore viability significantly compared to PIA-unstimulated neutrophils for strain 1 and strain 3 (p < .05). Neutrophils stimulated with 0.01, 0.1, 1, and 10 µg/ml PIA exhibited significantly lower zoospore viability than PIA-unstimulated neutrophils for strain 2 (p < .05). IL-8 can be used as a biomarker for monitoring vascular pythiosis cases treated with the PIA vaccine. Also, anti-P. insidiosum activity of PIA-stimulated neutrophils was probably due to the disruption of cellular activity in zoospores rather than the mechanisms based on the formation of NETs.

P131 Optimization of MTT assay protocol in Pythium insidiosum zoospores incubated together with neutrophils

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM

 

Objectives

The tetrazolium-based MTT assay is widely used to assess cell viability. This colorimetric assay measures cell viability through the enzymatic reduction of MTT, a yellow water-soluble tetrazolium dye, to purple-colored formazan crystals. The zoospores of Pythium insidiosum are the infective form causing pythiosis. There remains a lack of standardized protocol for P. insidiosum zoospore viability assay. Here, we optimized the MTT assay to assess the activity of neutrophils on zoospores.

Methods

Neutrophils and zoospores were incubated for 2 h, 4 h, and overnight at 37°C. Neutrophils were lysed in water (pH = 11), MTT was added to each well and incubated at 37°C for 2 h. Then, SDS-HCl solution was added to each well, and absorbance at 570 nm was measured using a microplate reader. The percentage of viable zoospores was then determined.

Results

The viable zoospores metabolized MTT to insoluble purple formazan product. The zoospores germinated into hyphae when incubated for ˃2 h. Because of the rapid germination of zoospores into hyphae, reliable results would be obtained with an optimum incubation time of 2 h for the zoospores.

Conclusion

The simplicity and low cost of the assay make it a valuable tool for zoospore viability studies, with a focus on immunology and immunotherapy.