Oral Presentation Lorne Infection and Immunity 2022

Single cell transcriptomics provides insights into innate and adaptive immune responses to malaria (#43)

Tinashe G Chabikwa 1 , Dean W Andrew 1 , Jessica Loughland 1 , Kim Piera 2 , Bridget Barber 1 , Arya SheelaNair 1 , Matthew Grigg 2 , Timothy William 3 , Nick Anstey 2 , Michelle Boyle 1
  1. QIMR Berghofer Medical Research Institute, Brisbane, QLD, Australia
  2. Menzies School of Health Research, Charles Darwin University, Darwin, NT, Australia
  3. Infectious Diseases Society, Sabah-Menzies School of Health Research Clinical Research Unit, Gleneagles Medical Centre, Kota Kinabalu, Sabah, Malaysia

Malaria is caused by Plasmodium ssp. parasites, with 3.2 billion people estimated to be at risk of infection. The development of effective malaria vaccines has been hampered by poor understanding of naturally acquired immunity. Plasmodium spp. are complex organisms with potentially thousands of immune targets, hence a systems biology approach, combining immunology and "omics" tools i.e., transcriptomics, proteomics and bioinformatics can help to identify novel and potentially effective vaccine candidates. To obtain greater insights into human immune responses to malaria, we used of single-cell RNA sequencing (scRNA-seq) to characterise distinct immune cell subsets in PBMCs collected from patients during acute malaria (day0), and at convalescence (7 and 28 days post treatment). 14 major cell subsets were identified using canonical and lineage markers, with only small changes to cell proportions with infection. We found that during acute infection, genes involved in pattern recognition, TLR1, TLR7, TLR8 and phagocytosis including FCGR1A/CD64, CR1 and CD36 are upregulated during acute infection. In contrast, chemokines and cytokines TNF, IL1A and IL1B, CCL3 and antigen-presenting molecules HLA-DR/B were downregulated during infection, consistent with immunosuppressive monocyte phenotypes. The functional diversity of monocytes was highlighted by the downregulation of CCL2 (MCP-1) during acute infection in CD14 but not CD16 Monocytes. An enrichment analysis of cis-regulatory elements upstream of DEGs revealed IRF1 and P53 as potential upstream regulators of CD16 Monocytes; these TFs have previously been previously associated with protection from malaria disease. Among CD4 T cells, Th1-regulatory T (Th1 cells that co-produce IFNy and IL10 - Tr1) cells were the most transcriptionally active with genes coding for anti-inflammation proteins including, STING as well as co-inhibitory receptors (CIRs) such as PDCD1/PD1, CTLA4, and TIM3 upregulated during acute infection. LAG-3 a key inhibitory receptor on antigen activated T-cells, was highly upregulated in Th1 and Tr1 cells during acute infection, while the anti-inflammatory cytokine IL10 was upregulated in Tr1 cells during acute infection. Together, data highlights the major importance of anti-inflammatory responses in both innate and adaptive cell subsets in modulating immune responses during acute infection in uncomplicated malaria.