Background: Monocytic surface expression of tissue factor (TF) may contribute to sepsis-associated coagulopathy. Monocytes are divided into three subsets that differ in functions: classical, intermediate, non-classical.

Aims: To investigate TF expression between monocytic subsets during sepsis.

Methods: Participants were recruited from four UK intensive care units (ICU). Blood samples were taken from two cohorts, those critically ill with a diagnosis of sepsis (sepsis cohort, n=18) and those who were critically ill without sepsis (critically ill cohort, n=10). Individuals with sepsis had microbiological confirmation of infection. Those in the sepsis cohort who survived to be discharged from ICU were consented for a further blood sample (sepsis recovery subgroup, n=10). Monocyte TF surface expression was measured with whole blood flow cytometry. Significance was calculated using paired and unpaired t-tests. Informed consent was taken when possible. Personal and professional consultees were used if an individual did not have capacity. Ethical approval was granted by a medical ethics committee.

Results: Both the sepsis and the critically ill groups were evenly matched, with no significant differences in age, sex, length of stay in ICU, organ support or monocyte count.
There was no difference between the total monocytic TF expressions between the critically ill and sepsis cohorts as well as between those with and without coagulopathy (platelet < 150 X 10⁹/L, prothrombin time >15 sec, activated partial thromboplastin time >35 sec or fibrinogen < 1.5 g/L). Total monocyte TF surface expression did increase following recovery from sepsis (Fig 1). The sepsis cohort had higher TF surface expression on the intermediate and non-classical subsets compared to the critically ill group. Following recovery from sepsis, there was an increase in the classical monocyte surface expression of TF (Fig 2).

Conclusions: Monocytic subsets vary TF surface expression during and on recovery from sepsis. This was no correlation between monocyte TF surface expression and coagulopathy.

[Fig 1: Total monocytic TF. A- critically ill & sepsis. B- sepsis & sepsis recovery **p<0.01. C- coagulopathic (red) & non-coagulopathic (black)]

[Fig 2: Monocyte subset TF surface expression during critical illness, sepsis and recovery from sepsis. *p<0.05, **p<0.01. ****p<0.0001.]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/the-tissue-factor-surface-expression-of-monocyte-subsets-during-sepsis/