Abstract Body (Do not enter title and authors here): Background: Increased risk of thrombotic outcomes has been observed during respiratory infections. This phenomenon likely involves platelet-leukocyte crosstalk via pattern recognition receptors (PRRs), including Toll-like receptors (TLR), Retinoic acid-inducible gene I-like receptors (RLR) and cGAS.

Purpose: We studied correlations between PRRs and select pro-thrombotic/procoagulant transcripts (ITGA2B, GP1BA, GP9, GP5, GP6, PF4, PF4V1, F13A1, SELP, SERPING1) in platelets and leukocytes of COVID19 (α-δ variants) patients; and determined if those correlations were present in blood from patients with 3 respiratory infections (COVID19, Influenza, Tuberculosis-TB).

Methods: RNA sequencing data of platelets and leukocytes isolated from COVID19 patients (n=10) and non-infected controls (n=15) was generated using AmpliSeq. Whole blood RNAseq was obtained from public databases for COVID19 (GSE217948), influenza (GSE161731), and TB patients (0m-peak infection, GSE181143). Transcripts with significantly greater mean expression in infected patients versus the respective control were assessed for positive correlations with PRRs using Spearman’s correlation coefficients. Data was analyzed in R.

Results: Platelets and leukocytes showed distinct patterns of the top five highest expressed PRRs, based on BaseMean (Platelets: TLR9>DDX58>IFIH1>CGAS>TLR4, Leukocytes: TLR4>IFIH1>DDX58>TLR8>TLR2). PRR that were significantly increased in COVID19 platelets versus controls were DDX58 (p=0.017) and IFIH1 (p=0.005); in leukocytes only IFIH1 (p=0.015) showed significant difference. The only overlapping correlation between a PRR and transcript in the two cell populations was TLR1 with F13A1 (platelets, R=0.56, p=0.04; leukocytes, R=0.56, p=0.02). In COVID19 platelets, TLR9 correlated with GP1Ba (R=0.62, p=0.002); DDX58 correlated with GP9 and PF4; and IFIH1 correlated with GP9 and GP6. In COVID19 leukocytes, IFIH1 and DDX58 correlated with SERPING1. In whole blood RNAseq analysis of all 3 infections, only DDX58 and TLR1 uniformly associated with PF4 and F13A1, respectively. Surprisingly, correlations between PRRs and the listed transcripts overlapped predominantly between COVID19 and acute TB, but not with influenza.

Conclusion: Platelets and leukocytes show distinct patterns of PRR expression and correlations with pro-thrombotic/procoagulant transcripts. Whole blood correlations between PRRs and thrombotic transcripts in COVID19 infection demonstrate more overlap with TB than influenza.