SOD3 suppresses early cellular immune responses to parasite infection.

Host immune responses are tightly controlled by various immune factors during infection, and protozoan parasites also manipulate the immune system to evade surveillance, leading to an evolutionary arms race in host‒pathogen interactions; however, the underlying mechanisms are not fully understood. We observed that the level of superoxide dismutase 3 (SOD3) was significantly elevated in both Plasmodium falciparum malaria patients and mice infected with four parasite species. SOD3-deficient mice had a substantially longer survival time and lower parasitemia than control mice after infection, whereas SOD3-overexpressing mice were much more vulnerable to parasite infection. We revealed that SOD3, secreted from activated neutrophils, bound to T cells, suppressed the interleukin-2 expression and concomitant interferon-gamma responses crucial for parasite clearance. Overall, our findings expose active fronts in the arms race between the parasites and host immune system and provide insights into the roles of SOD3 in shaping host innate immune responses to parasite infection.

Development of Nested PCR and Duplex Real-Time Fluorescence Quantitative PCR Assay for the Simultaneous Detection of Theileria equi and Babesia caballi.

Equine piroplasmosis (EP) is a type of blood protozoan disease caused by tick-borne parasites, Theileria equi (T. equi), Babesia caballi (B. caballi) and Theileria haneyi. While many studies have been conducted on EP diagnosis, diagnostic methods exhibiting high sensitivity and specificity remain lacking. Therefore, nested PCR (nPCR) and duplex real-time fluorescence quantitative PCR (qPCR) that can simultaneously detect both T. equi and B. caballi causing agents were established and compared. The two techniques were used to analyze 36 horse blood samples for EP. This set of samples was also detected by a multinested PCR (mnPCR) targeting the EMA-1 gene of T. equi and the RAP-1 gene of B. caballi. By nPCR, duplex real-time fluorescence qPCR and mnPCR, infections with B. caballi were detected in 16.67% (6/36), 2.78% (1/36), 19.44% (7/36) of the horses, respectively. The T. equi prevalence was 58.33% (21/36) by the nPCR, 33.33% (12/36) by the duplex real-time fluorescence qPCR and 2.78% (1/36) by the mnPCR. The overall prevalence of infection with mixed parasites by nPCR was 5.56% (2/36), by duplex real-time fluorescence qPCR was 2.78% (1/36) and by mnPCR 0% (0/36). Results suggest that nPCR can detect T. equi and B. caballi positive samples with good specificity and sensitivity, although distinguishing between the two parasites requires an electrophoresis with 4% agarose gels. The duplex real-time fluorescence qPCR can readily distinguish between T. equi and B. caballi infection, but with low sensitivity.