High Frequency Of Anti-Platelet Factor 4 /Heparin Antibodies In Patients With Lung Transplantation

Background : Heparin-induced thrombocytopenia (HIT) is characterized by the presence of antibodies directed against a complex of Platelet Factor 4 and heparin (PF4/H). These antibodies usually appear within 3 to 6 days after the beginning of heparin therapy, belong predominantly to IgG isotype, and activate platelets, leading to a thrombotic tendency. Murine models suggested that PF4/H complexes are T-cell dependent, but recent data suggested that marginal zone B cells which are stimulated in a T-cell-independent fashion are involved in the production of anti-PF4/H antibodies (PF4/H Ab). In agreement with these data, it was also described a high frequency of PF4/H Ab after liver transplantation, despite a strong immunosuppressive treatment. Aims: To analyze the incidence of PF4/H Ab in patients with bipulmonary transplantation and to identify a possible consequence of the presence these antibodies on thrombotic events. Patients u0026 Methods: Citrated blood samples of 55patients [33 cases of cystic fibrosis (60 %), 22 cases of chronic obstructive pulmonary disease (40 %)] with bipulmonary transplantation were analyzed on a first sample before the transplantation (D0) and on a second sample collected within 10 and 17 days after the surgery. (mean level ± 1.sd : 13.6 ± 1.7days). Extracorporeal membrane oxygenation (ECMO) was usually present during the surgery time, but for 4 patients, ECMO was needed up to 10 post-operative days. Patients were treated at least by a triple immunosuppressive regimen (tacrolimus, mycophenolic acid and corticosteroids) and usually by a low molecular weight heparin (enoxaparine or tinzaparine). Antibodies (Ig G, A and M isotypes) against anti-PF4/H complexes were detected using ELISA Asserachrom HPIA (Diagnostica Stago, France). A positive sample is provided, and plasma are considered positive when the absorbance (Abs.) of the plasma tested is above the Abs of the control plasma (CT). We calculated a ratio (Abs of the plasma tested)/(Abs. of the CT), and we considered that result was doubtful (DBT) when the ratio was between 0.8 and 1.2 and positive (POS) when u003e 1.2. In case of positivity, another assay, which detects only IgG isotype was performed (Asserachrom HPIA - IgG, Diagnostica Stago). Results: . Three patients (5.5 %) had PF4/H Ab at D0 (2 cases DBT and 1 POS), which were either IgA or IgM. For these 3 cases, the antibodies disappeared during the follow-up, spontaneously in 2 cases and in the last case possibly because of the use of rituximab. PF4/H Ab were observed in 20 patients (36.4%) on the second sample (10 DBT and 10 POS). In 12 cases out of 20, (60%) patients suffered from cystic fibrosis, indicating that there was no association of PF4/H Ab with the lung pathology. PF4/H Ab were detected in 2 patients with prolonged ECMO. Among the 10 POS plasma, 7 were of IgG isotype. Twenty-patients (40 %) experienced a thrombotic event within the 3 months following the transplantation: 6 of them (27.3 %) had PF4/H Ab, a frequency which was not significantly different from the frequency of PF4/H Ab in patients without thrombosis (42.4 %, p = 0.39). Due to a high frequency of pulmonary infections, leukocyte counts were increased at D0 in patients with PF4/H Ab (12.9 ± 7 x10 9 /L) as well as in patients without these antibodies (11.7 ±4.9 x10 9 /L), and remained elevated when the second sample was analyzed (respectively 15.5 ± 9.3 and 16.9 ± 12.5 x10 9 /L). There were no significant differences between patients with or without PF4/H Ab. Platelet counts were not different at D0 between both groups (312 ± 172 and 312 ± 149 x10 9 /L) but during the follow-up, patients with PF4/H Ab had a mean level of platelets (498 ± 194 x10 9 /L) higher than patients without PF4/H Ab (404 ± 255 x10 9 /L), but it did not reach statistical significance ( p = 0.069). No patient developed clinical HIT. Lastly, tacrolimus levels were not significantly different in both group of patients (7.3 ± 2.7 ng/mL in patients with PF4/H Ab versus 6.4 ± 2.6 ng/mL in patients without PF4/H Ab) making insufficient immunosuppression in immunized patients unlikely. Conclusion: Despite a strong immunosuppressive regimen, a high frequency of PF4/H Ab is observed in patients undergoing lung transplantation, indicating that T cells likely have a limited role in the immune response to PF4/H complexes in humans. From these results, it is not evident that the presence of PF4/H Ab is implicated in physiopathological processes in lung transplantation. Disclosures Van Dreden: Diagnostica Stago: Employment.