Derangements of TLR2 Likely Play a Significant Role in the Thrombosis of Ph(-) Myeloproliferative Neoplasm

Introduction . We had previously reported that TLR 2 levels were significantly elevated in patients with polycythemia vera and MPN ( PV , ET, MF grouped together ) and TLR2 levels were related to JAK2 mutation and leukocytosis ( Blood (2022) 140 (Supplement 1): 12185–12186.). Since MPN has increased incidence of thrombosis in patients with JAK2V617F mutation and leukocytosis , therefore , current studies were done to test whether TLR-2 is related to thrombosis in MPN . In vitro platelet activation ( an pre-thrombotic marker) and clinical episodes of thrombosis were then investigated. .

Material and Methods. 119 patients ( 51ET, 37 PV, 31MF, 21 CTR) were studied .1) platelet activation. : The diluted blood was incubated with platelet agonists Pam3CSK4 (TLR2 agonist) or lipopolysaccharide (LPS) (TLR4 agonist) for 15 minutes at room temperature , then platelet activation was measured by Flow cytometry assaying CD40L, P-selectin, PAC-1 and LPI ( leukocyte-platelet-interaction). We obtained more consistent results from the LPI methods . Therefore, LPI methods were used to measure the platelet activation. LPI method was measured by CD45 and CD41 antibodies (Miltenyi Biotec, Auburn, CA), and platelet activation were measured as the percentage of CD45 cells with aggregated CD41. To test whether TLR2 or TLR4 were responsible for the LPI response ,TLR2 inhibitor C29 (InvivoGen, San Diego, CA) or the TLR4 inhibitor C34 ((Sigma-Aldrich, St. Louis, MO) were added to the LPI assay. Effects of inhibitions were measured by fold-changes which were calculated by dividing the LPI values after activation by either Pam3CSK4 (TLR2 agonist) or LPS (TLR4 agonist), with or without added inhibitors, by the LPI values before activation or inhibition.

Results . 1) As shown in Fig A, a) un-activated MPN (U-MPN) patients had more LPI than un-activated controls (u-CTR), with mean ± SE of 13.01 ± 1.12 and 5.01 ± 0.97 in U-MPN and U-CTR, respectively (P<0.01). This is consistent with previous reports that un-activated MPN patients have more intrinsically activated platelets than un-activated controls .b) Greater LPI response by activation by Pam3CSK4, (TLR2 agonist ) than by LPS ( lipopolysaccharide)) (TLR4 agonist) . MPN and controls ( mean ± SE ) were of 22.25 ± 0.99 and 10.46 ± 0.44 ( by Pam3CSK4) and 12.12 ± 2.16 and 4.34 ± 0.32 ( by LPS) (P<0.0005) respectively . 2). Fig B showed the TLR2 inhibitor C29 significantly suppressed LPI ( measured by fold-changes ) , in un-activated MPN (0.38 ± 0.05), activated controls (0.42 ± 0.11), and activated MPN (0.42 ± 0.05). Conversely, the TLR4 inhibitor C34 had no inhibitory effect on un-activated MPN (0.98 ± 0.03), activated MPN (1.02 ± 0.02), or activated controls (0.84 ± 0.06) . 3) As shown in Table 2 , TLR 2 levels elevated Patients ( TLR2-E) ( defined as more than mean plus 2 standard deviation of controls (> 310 MFI) , have more thrombosis episode (29%) than TLR2 -normal patients (11%) .

Conclusion . TLR2 likely plays a significant role in thrombosis in MPN patients on the basis : 1) JAK2 mutated patients have more TLR2 levels 2) TLR2-E patients have more leukocytosis than TLR-N patients 3) LPI was significantly elevated with TLR2 agonist ( Pam3SK4) but not by TLR4 agonist ( LPS) , and LPI was significantly decreased by TLR2 inhibitor and not by TLR4 inhibitor. 4) clinical evidence of more thrombosis in TLR -E patients than TLR-N patients.