The serine protease cofactor factor V is synthesized by lymphocytes

Area of Science:

• Immunology
• Hematology
• Molecular Biology

Background:

• Cellular immune responses activate CD4+ T cells, leading to tissue factor expression and coagulation cascade initiation.
• Thrombin, generated by the coagulation cascade, influences cellular responses and fibrin deposition.
• The role of extravascular cells in immune effector pathways, particularly in providing coagulation cofactors, was unclear.

Purpose of the Study:

• To investigate the potential for extravascular cells, specifically lymphocytes, to provide the cofactor factor Va.
• To determine if lymphocytes transcribe and synthesize factor V, a crucial component of the coagulation cascade.

Main Methods:

• Reverse transcription followed by polymerase chain reaction (RT-PCR) to detect Factor V mRNA in human lymphoid cells.
• Cloning of factor V cDNA from a T cell cDNA library for confirmation.
• Northern blot analysis to confirm the presence and abundance of factor V mRNA in T cell lines and lymphocytes.
• Immunocytology using a factor V monoclonal antibody (mAb) to detect intracellular factor V protein.

Main Results:

• Factor V mRNA was detected in human lymphoid cells, including T lymphoma cell lines, unstimulated lymphocytes, and stimulated T cells.
• Factor V cDNA cloned from a T cell library showed high sequence similarity to hepatic factor V mRNA.
• Northern blot confirmed a approximately 7-kb factor V mRNA transcript in T cells.
• Immunocytology revealed intracellular, but not surface, factor V in T lymphocytes.

Conclusions:

• Human lymphocytes are capable of transcribing and synthesizing factor V.
• Lymphocytes can provide essential cofactors for the coagulation cascade at extravascular sites.
• This discovery offers a new perspective on the contribution of lymphocytes to inflammatory and immune effector functions.