Fig 1: Role of platelets in B. burgdorferi-induced cytokine production. (A) FDR-corrected P-values of correlations between circulating platelet parameters and cytokine production by PBMCs stimulated ex-vivo in a cohort of 489 healthy participants. Platelet markers include ADP- and CRP-XL-induced platelet P-selectin (APR and CPR); platelet-fibrinogen binding to either ADP or CRP-XL (AFR and CFR); platelet-monocyte complexes (PMC); CXCL7 levels, CXCL7 levels corrected for platelet count (CXCL7/PLT); total platelet count (PLT). The correlation coefficients of the statistically significant correlations are provided, the non-significant correlation coefficients are not displayed. (B-C) Percentage of P-selectin- and fibrinogen positive platelets (n = 6 healthy volunteers), determined by flow cytometry after 3hr stimulation with increasing doses of B. burgdorferi or the positive control ADP. Bb5/6/7 = stimulation with B. burgdorferi 10^5/6/7 spirochetes/ml. (D) CXCL7 secretion in cell-free supernatants of platelets from healthy volunteers (n = 6) stimulated for 3hr with increasing doses of B. burgdorferi or the positive control ADP. Expression of the gene PPBP (CXCL7) (E) and CCL5 (F) in physician-confirmed LB patients (including both EM and multiple EM) at different time points (n = 29) compared to healthy controls (n = 13). Data were extracted from the NCBI GEO database, accession number GSE63085. Data are represented as median±IQR of fragments per kilobase of transcript per million mapped reads (FPKM). The concentration of both CXCL7 (G) and CCL5 (H) were elevated in the plasma of 82 EM patients, including 14 patients with multiple timepoints, compared to 19 healthy controls. Cytokine production of IL-1ß (I) and TNFa (J) in platelet-poor (PP) PBMCs from healthy volunteers (n = 6) stimulated for 24hr with B. burgdorferi in the presence of rhCXCL7 (20µg/ml). Ns = not statistically significant, *P < 0.05, **P < 0.01, ***P < 0.0001 calculated using independent-samples Mann-Whitney U test for comparing HC and LB patient cohort and Wilcoxon matched-pairs signed ranked test for paired testing when comparing LB patient different time points in panels E-H. Wilcoxon matched-pairs signed ranked test was used in panels I and J.