Background: The detection of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) by multimeric protein complexes, known as inflammasomes, triggers an inflammatory response, which is a critical component of the innate immune system. This inflammatory response plays a pivotal role in host resistance against parasitic infections, presenting a significant global health challenge. Methods: We systematically searched for relevant articles from the Pubmed and the Web of Science database to summarize current insights into how inflammasomes function in preventing infections caused by the apicomplexan parasites Toxoplasma and Plasmodium. Results: In vivo and in vitro studies have extensively explored inflammasomes such as the absent in melanoma 2 (AIM2), NLR family pyrin-containing protein 1 (NLRP1), NLRP3, and NLRP12 inflammasomes, alongside noncanonical inflammasomes, with particular emphasis on the NLRP1 and the NLRP3 inflammasome during Toxoplasma gondii infection or the AIM2 and the NLRP3 inflammasome at various stages of Plasmodium infection. Toxoplasma gondii interacts with inflammasomes to activate or inhibit immune responses. Conclusions: Inflammasomes control parasite burden and parasite-induced cell death, contribute to immune recognition and inflammatory responses and thus influence apicomplexan parasite-associated pathogenesis and the severity of clinical outcomes. Hence, inflammasomes play crucial roles in the progression and outcomes of toxoplasmosis and malaria. A comprehensive understanding of how parasitic infections modulate inflammasome activity enhances insight into host immune responses against parasites. Graphical

Background: Acanthamoeba spp., which are free-living protozoan parasites, are etiological agents for Acanthamoeba keratitis and granulomatous amoebic encephalitis. Macrophages participate in the host defense response to resist Acanthamoeba spp. This study examined the effect of Acanthamoeba castellanii cysteine protease 3 ( Ac CP3) on macrophage activation during inflammatory responses and explored the underlying mechanisms. Methods: The effects of recombinant Ac CP3 (r Ac -CP3) stimulation on inflammatory factor levels and macrophage polarization were examined using murine macrophage cells (RAW264.7 cells). Western blotting assay was carried out for analyzing TLR4/NF‑κB pathway-related protein levels. In addition, phosphorylated NF-κB was examined for its nuclear transport using immunofluorescence. The effect of the NF-κB inhibitor pyrrolidinedithiocarbamate ammonium (PDTC) on r Ac -CP3-induced M1 polarization was analyzed. Furthermore, RAW264.7 cells were co-cultivated using Ac CP3 knockdown trophozoites to examine indicators of M1 polarization and pathway-related protein levels. Results: As revealed by quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and enzyme-linked immunosorbent assays, treatment with r Ac -CP3 upregulated the mRNA, protein, and secretion levels, respectively, of Il6, Il1b, Tnfa, and Ifng in macrophages. Flow cytometric analysis demonstrated that r Ac -CP3 promoted Cd86 ⁺ cell (macrophage) proliferation. Additionally, r Ac -CP3 upregulated Nos2 expression and nitric oxide (NO) production, indicating that r Ac -CP3 promotes macrophage polarization toward an M1-like phenotype. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis demonstrated that the NF-κB pathway was among the top 20 significantly enriched pathways. Treatment with r Ac -CP3 upregulated the levels of Tlr4, p-Rela, and p-Nfkbia in RAW264.7 cells. Immunofluorescence analysis demonstrated the nuclear translocation of p-Rela. Pretreatment with the NF-κB inhibitor PDTC downregulated the Tlr4, p-Rela, and p-Nfkbia levels in r Ac -CP3-treated cells. Additionally, PDTC significantly mitigated the r Ac -CP3-induced upregulation of Nos2, NO and pro-inflammatory factor production. Ac CP3 knockdown decreased the number of Cd86 ⁺ cells and suppressed Acanthamoeba trophozoite-induced Nos2 upregulation and NO production. Additionally, Ac CP3 knockdown downregulated Tlr4, p-Rela, and p-Nfkbia in RAW264.7 cells. PDTC and Ac CP3 knockdown suppressed the r Ac -CP3-induced M1 macrophage polarization. Conclusions: Ac CP3 promotes M1 macrophage polarization through the TLR4/NF-κB pathway and may exacerbate inflammation through upregulating pro-inflammatory cytokines. Graphical